<%BANNER%>

Documenting dodern and ancient methane release from cold seeps using deep-sea benthic foraminifera

University of Florida Institutional Repository

PAGE 1

DOCUMENTING MODERN AND ANCIENT METHANE RELEASE FROM COLD SEEPS USING DEEP-SEA BENTHIC FORAMINIFERA BY SHELLEY ANNE DAY A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2003

PAGE 2

Copyright 2003 BY SHELLEY ANNE DAY

PAGE 3

iii ACKNOWLEDGMENTS This research was funded by NOAANURP Grant numbers UAF98-0043 and FP007222. There are many people I wish to th ank for their help and support on this project. First, I would like to thank my a dvisor, Dr. Jonathan Martin, for providing me with this research opportunity and his invaluable guidance and editorial assistance. I would also like to thank my other co mmittee members, Dr. Anthony Randazzo, Dr. David Hodell and Dr. John Jaeger, for their time and advice. I thank Anthony Rathburn and Elena Prez for contributing live foraminife ra to this study, as well as assisting in identifying fossil foraminifera. In additi on, I would like to tha nk Joris Gieskes for contributing pore water solute data. I thank Ja son Curtis for his endless assistance in the stable isotope lab. Finally, I would like to thank my family for providing me with support and guidance throughout my life.

PAGE 4

iv TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iii LIST OF TABLES.............................................................................................................vi LIST OF FIGURES..........................................................................................................vii ABSTRACT....................................................................................................................... ..x CHAPTER 1 INTRODUCTION...........................................................................................................1 The Correlation between Climate and Methane.............................................................2 Methane and the Stable Isotopic Com position of Benthic Foraminifera........................6 Pore-water Chemistry, Vital Effects, and Foraminiferal Composition....................7 Diagenesis................................................................................................................8 Objective/Scope of Research..........................................................................................9 Study Areas...................................................................................................................1 0 Monterey Bay.........................................................................................................10 Eel River................................................................................................................12 2 METHODS....................................................................................................................1 5 Field Sampling..............................................................................................................15 Monterey Bay.........................................................................................................15 Eel River................................................................................................................17 Foraminiferal Preparation and Analyses.......................................................................17 Live Foraminifera Preparation...............................................................................17 The Rose Bengal Staining Technique....................................................................18 Fossil Foraminifera Preparation.............................................................................20 Foraminiferal Isotope Analyses.............................................................................20 Pore-water DIC Analysis..............................................................................................21 Carbon Isotopes......................................................................................................21 Pore Water Solutes.................................................................................................22 SEM Analysis...............................................................................................................22

PAGE 5

v 3 RESULTS..................................................................................................................... .24 Pore Fluid Geochemistry..............................................................................................24 Monterey Bay.........................................................................................................24 Eel River................................................................................................................27 Stable Isotopic Signatures of Foraminiferal Carbonate................................................30 Monterey Bay.........................................................................................................30 Carbon isotopes................................................................................................30 Oxygen isotopes...............................................................................................36 Eel River................................................................................................................36 Carbon isotopes................................................................................................36 Oxygen isotopes...............................................................................................40 Scanning Electron Microscope (SEM) Micrographs....................................................44 4 DISCUSSION................................................................................................................48 The Effects of Methane on Pore Water Composition...................................................48 Pore Water, Methane, and the Isotopic Composition of Foraminiferal Tests........50 Diagenesis as a Contributing Factor to Isotopically Light Foraminiferal Carbonate............................................................................................................. 51 Diagenesis in the Eel River Basin..........................................................................54 Stable Isotopic Compositions ....................................................................................... 58 The Variation in Foraminiferal Carbon Isotopes...................................................58 The Relationship between Methane, Pore Water 13C, and Foraminiferal Carbonate...............................................................................................................61 A Comparison of the Isotopic Composition of Seep and Non-seep Foraminifera63 Foraminiferal 18O Compositions..........................................................................69 A Comparison of Foraminiferal Oxygen Isot opes from Seep and Non-seep Sites71 APPENDIX 5 CONCLUSIONS............................................................................................................74 A PORE WATER CHEMISTRY.....................................................................................77 B FORAMINIFERAL ISOTOPE DATA.........................................................................82 C SEM PHOTOMICROGRAPHS...................................................................................95 LIST OF REFERENCES.................................................................................................102 BIOGRAPHICAL SKETCH...........................................................................................108

PAGE 6

vi LIST OF TABLES Table page 1-1. A list of the amount of organic carbon (g) stored in the various reservoirs................4 1-2. Some of the similarities and differenc es between the Monterey Bay and the Eel River basin.............................................................................................................14 2-1. A listing of cores collected from Monterey Bay and their designated use................16 2-2. The location and designated use of Eel River cores..................................................17 2-3. List of terms used in this paper to describe foraminifera..........................................19 2-4. Foraminifera used for SEM analysis.........................................................................23 3-1. The 13CDIC values of supernatant fluids taken from the tops of cores designated for pore water analyses..........................................................................................27 3-2. A statistical comparison of Monterey Bay foraminifera...........................................31 3-3. A statistical comparison of fossil (? ) foraminifera from Eel River Basin.................40 4-1. A comparison of the mean 13C and 18O values of U. peregrina from Invertebrate Cliffs (1780 PC30), Clam Flats (1781 PC31), and Eel River (2052 LC2, LC4, and LC5)................................................................................................................54 4-2. A comparison of the mean 13C values and standard deviat ions of live foraminifera from Clam Flats (PC31) and I nvertebrate Cliffs (PC30).......................................62

PAGE 7

vii LIST OF FIGURES Figure page 1-1. Map showing the location of Monterey Bay cold seeps, including Clam Flats and Invertebrate Cliffs, which we re sampled in this study...........................................11 1-2. A map of the northern California margin showing a portion of the Eel River Basin, which was sampled for this study..........................................................................13 2-1. A picture of the seepage area sample d from Invertebrate Cliffs located at approximately 955 meters water depth (Dive 1780)..............................................16 3-1. Pore water calcium profiles for M onterey Bay clam beds (Dive 1780 PC79, Invertebrate Cliffs and Di ve 1781 PC80, Clam Flats)...........................................25 3-2. Pore water sulfide (HS-) profiles for Monterey Bay clam beds (Dive 1780 PC79, Invertebrate Cliffs and Di ve 1781 PC80, Clam Flats)...........................................25 3-3. Pore water alkalinity profiles from Monterey Bay clam beds (Dive 1780 PC79, Invertebrate Cliffs and Di ve 1781 PC80, Clam Flats)...........................................26 3-4. The 13CDIC profile of pore water from Monter ey Bay clam beds (Dive 1780 PC79, Invertebrate Cliffs a nd 1781 PC80, Clam Flats)....................................................26 3-5. Calcium pore water profiles for Eel Ri ver Dive 2052: PC16 (bacterial mat), PC8 (clam bed), and PC19 (bubble site)........................................................................28 3-6. Pore water sulfide prof iles for Eel River Dive 2052: PC16 (bacterial mat), PC 8 (clam bed) and PC19 (bubble site).........................................................................28 3-7. Sulfate ion pore water profiles from Ee l River Dive 2052: PC16 (bacterial mat), PC 8 (clam bed) and PC19 (bubble site)................................................................29 3-8. Pore water alkalinities for Eel River Dive 2052: PC8 (clam bed), PC16 (bacterial mat), and PC19 (bubble site).................................................................................29 3-9. Pore water 13CDIC for Eel River Dive 2052 PC16 (b acterial mat), PC8 (clam bed) and PC19 (bubble site)...........................................................................................30 3-10. Dive 1780 HPC5 and PC30 (Inve rtebrate Cliffs clam bed) Uvigerina peregrina 13C vs. depth.........................................................................................................32

PAGE 8

viii 3-11. Dive 1780 HPC5 and PC30 (Inve rtebrate Cliffs clam bed) Epistominella pacifica 13C vs. depth.........................................................................................................32 3-12. Dive 1780 HPC5 and PC30 (Inve rtebrate Cliffs clam bed): Bulimina mexicana 13C vs. depth.........................................................................................................33 3-13. Dive 1780 (Invertebrate Cli ffs clam bed) HPC5 and PC30 Globobulimina pacifica 13C vs. depth...........................................................................................33 3-14. Dive 1781 PC31 (Clam Flats clam bed) Uvigerina peregrina 13C vs. depth........35 3-15. Dive 1781 PC31 Clam Flats (clam bed): Epistominella pacifica Bulimina mexicana Globobulimina pacifica and Planulina species 13C vs. depth...........35 3-16. Dive 1780 HPC 5 and PC30 (Inve rtebrate Cliffs clam bed) Epistominella pacifica 18O vs. depth...........................................................................................37 3-17. Dive 1780 HPC5 and PC30 (Inve rtebrate Cliffs clam bed) Bulimina mexicana d 18 O vs. depth.........................................................................................................37 3-18. Dive 1780 (Invertebrate Cli ffs clam bed) HPC5 and PC30: Uvigerina peregrina 18O vs. depth.........................................................................................................38 3-19. Dive 1780 (Invertebrate Cli ffs clam bed) HPC5 and PC30 pacifica 18O vs. depth...........................................................................................38 Globobulimina 3-20. Dive 1781 PC31 (Clam Flats clam bed) Uvigerina peregrina 18O vs. depth........39 3-21. Dive 2052 long core 5 (bacterial mat): Uvigerina peregrina and Epistominella pacifica 13C vs. depth...........................................................................................41 3-22. Dive 2052 Long core 4 (clam bed): Epistominella pacifica and Uvigerina peregrina 13C vs. depth........................................................................................41 3-23. Dive 2052 Long core 2 (bubble site): Uvigerina peregrina Epistominella pacifica, and Bulimina mexicana 3-24. Dive 2052 long core 2 (bubble site): Uvigerina peregrina, Bulimina mexicana 13C vs. depth...................................................42 and Epistominella pacifica 18O vs. depth. ...........................................................42 3-25. Dive 2052 long core 4 (clam bed): Epistominella pacifica and Uvigerina peregrina 18O vs. depth........................................................................................43 3-26. Dive 2052 Long Core 5 (bacterial mat): Uvigerina peregrina and Epistominella pacifica 18O vs. depth...........................................................................................43

PAGE 9

ix 3-27 (a, b). A scanning electron micrograph of an Uvigerina peregrina from Monterey Bays Invertebrate Cliffs clam bed. (a) An overall shot of the test. (b) A close up of the test from the region identified in (a).......................................................45 3-28. A scanning electron micrograph of an Epistominella pacifica from Monterey Bay's Invertebrate Cliffs clam bed. (a). An overall view of the test. (b). A close-up of the test from the region identified in (a). ............................................46 3-29 (a,b). A scanning el ectron micrograph of a U. peregrina from Eel Rivers long core 4 (clam bed). (a) An overall view of the test. (b). A clos e-up of the region identified in (a).......................................................................................................47 4-1. A plot of the saturation indices (SI) versus depth for the bubble site (PC19, which corresponds to the foraminifera from long core 2)................................................56 4-2. A plot of the saturation indices (S I) versus depth for PC8 (clam bed, which corresponds to the foraminifera from long core 4)................................................56 4-3. A plot of the saturation indices (SI) versus depth for PC16 (bacterial mat, which corresponds to the foraminifera from long core 5)................................................57 4-4(a, b). The average 13C and standard deviation ( ) of U. peregrina from Invertebrate Cliffs (1780 PC30) and Clam Flats (1781 PC31) compared to values reported in the literature. (a). Actual bottom water d13C is not used; instead, the supernatant fluid from the core tops is substituted for bottom water (See text for discussion). (b). An estimated bottom water value of .3 is used for the calculation of the average 13C from Clam Flats and Invertebrate Cliffs. Note the difference in the scale of the x-axis from (a)...................................................67 4-5(a, b). The average 13C and standard deviation of U. peregrina from Eel Rivers Long core (LC) 4 (clam bed) and LC5 (bact erial mat), compared to those reported in the literature. (a). LC4 and LC5 are plotted using 13CDIC values obtained from supernatant fluid (see text for discussion). (b) LC4 and LC5 are replotted using Rathburn et al.s (2000) bottom water 13CDIC value....................68 4-6. A 18O comparison of live and fossil conspeci fic foraminifera from Clam Flats (1781 PC31)...........................................................................................................69 4-7. A plot of the 18O values of U. peregrina from Invertebrate Cliffs (1780 PC30) and Clam Flats (1781 PC31) relative to thos e values reported in the literature....72 4-8. A plot of the 18O values of U. peregrina from Eel River (2052) LC5 (bacterial mat), LC4 (clam bed) and LC2 (bubble site) relative to those values reported in the literature...........................................................................................................73

PAGE 10

x Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science DOCUMENTING MODERN AND ANCIENT METHANE RELEASE FROM COLD SEEPS USING DEEP-SEA BENTHIC FORAMINIFERA By Shelley Anne Day May 2003 Chair: Jonathan Martin Major Department: Geological Sciences Methane, which is a potent greenhouse gas and a highly reduced form of carbon, is a minor component of the atmosphere; how ever, large amounts of methane are stored in continental margin sediments as a component of pressure and temp erature sensitive gas hydrates. Dissociation of these hydrates and the release of methan e, which could have important climatic implications, have been inferred in the past based on the isotopic composition of fossil foraminifera in prior paleoceanographic studies. Little analogous data from modern seep sites exist to document the significa nce of released methane on foraminiferal isotop ic composition. Methane is commonly released from cold seep environments, which are ideal settings to investigate the relationship betw een methane and the is otopic composition of foraminifera. For this study the stable is otopic compositions of living (Rose Bengal stained) and fossil benthic fo raminifera from active seepag e sites in Monterey Bay (1000

PAGE 11

xi m) and the Eel River Basin (~520 m) on the Ca lifornia margin were used along with pore water chemistry to assess the effects of methane on foraminiferal carbonate. Live and fossil benthic foraminifera from these seep sites were found to have carbon isotopic compositions that are more variab le than the same species of foraminifera previously measured from non-seep sites on th e California and North Carolina margins. In general, the carbon isotopic values of the s eep foraminifera were similar to or up to a few per mil lighter than the isotopic values of foraminifera found in non-seep sites. The isotopic values of the seep foraminifera, however, are far from equilibrium with the ambient dissolved inorganic carbon pool, which ha s carbon isotopic values as light as -45‰ in the upper 5 cm of the core. This disequilibrium could indicate that the foraminifera have specific microenvironmen ts where calcification takes place, possibly near the surface or near bu rrows where seawater DIC ( 13CDIC approximately 0‰) would contribute more to the DIC pool. The isot opic composition of the DIC, which would vary with the episodic seepage of methane, does create variability in foraminiferal carbon isotope values. In contrast with the large disequilib rium observed among foraminifera and 13CDIC values in Monterey Bay, large negative car bon isotopic excursions, as light as -23‰, are seen in Eel River foraminifera. These light isotope ratios a ppear to result from postmortem precipitation of authigenic carbona te, which is in equilibrium with the 13CDIC, on the tests. Faster seepage rates or more profuse seepage at Eel River could cause authigenic carbonate pr ecipitation to occur in Eel River and not Monterey Bay. Therefore, variability in the isotopic compos ition of conspecific foraminifera appears to be a better indication of methane rel ease than absolute isotopic values.

PAGE 12

1 CHAPTER 1 INTRODUCTION Methane, which contains a highly reduced form of carbon, plays an important role in many of the biological and geochemical processes on Earth. Although methane is a minor component of the atmosphere, it has ne vertheless received considerable attention due to its potential as a powerful greenhouse gas. The realization that large amounts of methane are stored subaqueously, frozen as “gas hydrates” within a temperature and pressure sensitive solid framework of water molecules, has led to suggestions that methane may have played an important ro le in the Earth’s climatic history ( Wefer et al., 1994 ; Dickens et al., 1995 ; Kennett et al., 1996 ). For instance, the abrupt warming which characterizes the first few decades of interg lacials and interstadials is accompanied by rapid increases in atmospheric methane ( Severinghaus et al., 1998 ). Gas hydrates are temperature and pressure sensitive; therefore, the dissociation of gas hydrates would result from warmer clima tic conditions and warmer waters or lower sea levels. Methane released from subaque ous gas hydrates could diffuse up through the sedimentary column, be oxidized by bacteria and contribute bicarbonate to the dissolved inorganic carbon pool and possibly be incorpor ated into foraminiferal tests. Using foraminifera as a proxy, Kennett et al. ( 2000 ) proposed that changes in thermohaline circulation over the past 60,000 years in the Sa nta Barbara Basin resulted in fluctuations in water temperature. In tu rn, variable water temperatur es resulted in the periodic destabilization of gas hydrates, which contri buted isotopically light carbon and heavy

PAGE 13

2 oxygen to planktonic and benthic foraminifera living within the Santa Barbara Basin ( Kennett et al., 2000 ). If the isotopic values obtained from fo ssil foraminifera preserve ancient porewater conditions, then the stratigraphic variat ion in these values w ould provide a record of methane seepage. In addition to the anomalously negative carbon isotopic compositions of fossilized benthic foramini fera suggested to result from gas hydrate dissociation ( Kennett et al., 1996 ; 2000 ; Dickens et al., 1995 ; Wefer et al., 1994 ), diverse carbon isotopic compositions are reported fo r live and fossil benthic foraminifera inhabiting methane seep sites ( Sen Gupta and Aharon, 1994 ; Rathburn et al., 2000 ). These recent studies ( Rathburn et al., 2000 ; Williams et al., 2002 ) question the validity of a direct link between methane seepage and a light 13C foraminiferal test value. Seepage instead may be inferred based on the hetero geneity of carbon isotope values and the similarity of oxygen isotope values among numer ous tests collected from identical depths (i.e., times of deposition). There is, however, a scarcity of analogous data available from modern (living) foraminifera to evaluate this hypothesis. Therefore, it is the intent of this work to show that the magnitude of the 13C of benthic foraminifera (live and fossil) alone does not reliably indicate methane and associated dissolved inorganic carbon (DIC) venting from marine sediments; however, wh en numerous foraminifera from areas of seepage are analyzed, methane venting is manife sted in the heterogeneity of foraminiferal carbon isotope values among coexisti ng conspecific individuals. The Correlation between Climate and Methane In recent years, research focusing on the causes of global climate change, particularly global warming, ha s intensified. Greenhouse gase s, such as carbon dioxide

PAGE 14

3 and methane, which contribute to the global warming of the earth, are of particular concern. The effect that gr eenhouse gases have on the atmosphere not only depends on their concentrations bu t also on their residence times in the atmosphere and the width of their absorption bands. As a result of methane absorbing radiation in the wavelength band between 8000-12000 nm, where carbon dioxide is not an effective absorber, 1 kg of methane has the potential to absorb 21 times the infrared radiation as 1 kg of carbon dioxide ( Houghton et al., 1990 ). Thus, the carbon cycle and climate change could be significantly affected by the release of methane. One of the major reservoirs of methane is believed to be in gas hydrates formed and trapped in continental margin settings ( Kvenvolden, 1988 ). Natural gas hydrates are formed when a rigid framework of water molecules freezes in the presence of sufficient natural gase s; the water crystalliz es in a cubic lattice and traps the gas molecules ( MacDonald, 1990 ). Methane is the dominant gas found in most oceanic gas hydrates, representing grea ter than 98% of the total gas, although ethane, carbon dioxide, and hydrogen sulfide ma y also be significant in some regions ( Dickens, 2001 ). According to Kvenvolden ( 1988 ), the amount of methane currently stored within subaqueous gas hydrates may be in excess of 1019 g of methane carbon. This estimation exceeds the amount of methane stored in all other reservoirs combined (Table 1-1). The stability of gas hydrates is a functi on of temperature, pr essure, salinity, and gas concentration, with hydrat es commonly forming in the oc eans where water depths are between 300 and 2000 meters and temp eratures are less than 5 C ( Kvenvolden, 1988 ). Hydrates form rapidly, within minutes, both in free seawater and in sediments based on

PAGE 15

4 experiments conducted in the waters of Monterey Bay ( Brewer et al., 1997 ); similarly, the hydrates dissociated rapidly during the experiment, first with bubbles being emitted from the sediments and then with conti nuing gas expansion, the dissociating hydrates ruptured the cylinders ho using the experiment ( Brewer et al., 1997 ). In natural settings, once the gas hydrates are no longer within th e stability field, for example by changing ambient conditions (such as a pressure decr ease due to the removal of overburden), the gases may migrate upward through the sedime ntary column and reach the seafloor, depending upon the texture and porosity of th e sediment. Such emissions of methane (and other gases) at ambient seafloor temp eratures are often termed cold seeps. Table 1-1. A list of the amount of organic carbon (g) stored in the various reservoirs. Reservoir Amount of organic carbon (g) Gas hydrates >1019 All fossil fuel deposits 51018 Terrestrial soil, detritus, and peat 1.961018 Marine dissolved materials 9.81017 Terrestrial biota 8.31017 Atmosphere 3.61015 Marine biota 31015 Data from Kvenvolden ( 1988 ). The methane emitted from cold seeps may be either biogenic or thermogenic in origin. Biogenic methane is produced in sh allow sediments as a result of the microbial degradation of organic matter. Thermogenic methane results from the thermochemical dissociation of organic matter at high temperatures and depths (2-3 km). The two sources may be distinguished based on the carbon isotopic signature of the meth ane. In general, microbially produced methane is isotopically lig hter than thermogenic methane, which is characterized by 13C values ranging from -50 to -20‰ ( Whiticar, 1999 ). Biogenic

PAGE 16

5 methane typically exhibits 13C values less than -50‰ ( Whiticar, 1999 ). Regardless of its source, the 13C of methane is isotopically lighte r than the inorganic forms of carbon dissolved in seawater, which have a 13C of approximately 0‰ PDB. Therefore, if isotopically light methane reaches the sedime nt-water interface, it would decrease the 13C of DIC after being oxidized in the pore waters. These light isotope ratios are retained in the authigenic car bonate minerals that form from the isotopically light DIC; however, it is unknown whether benthic foraminife ra preserve these signatures. Inferring seepage based on benthic foraminiferal carbonate rather than authig enic carbonate would be valuable, as benthic foraminifera are ch aracterized by a relatively short lifespan (on the order of years) and would provide a st ratigraphic component, which may provide clues to the longevity of seepage. Today the majority of natural atmospheri c methane is produced as a result of bacterial decomposition in wetland environments ( Blunier, 2000 ). It has been proposed, however, that during former periods of rapid climate change, large quantities of methane were released to the oceans and atmosphere as a result of the disso ciation of gas hydrates ( Wefer et al., 1994 ; Dickens et al., 1995 ; Kennett et al., 1996 ; 2000 ). For instance, off Peru, Dickens et al. ( 1995 ) attributed a –2 to –3‰ shift in benthic foraminiferal 13C and 18O in less than 104 years (during the late Paleocene) to the dissociation of hydrates, which were thought to have destabilized due to a 4C increase in bottom water temperature ( Dickens et al., 1995 ). Additionally, in the Santa Barbara Basin, Kennett et al. ( 2000 ) attributed a large carbon isotopic excursion to hydrat e destabilization; this excursion was characterized by interstadial benthic foraminifera being lighter by up to 4‰ relative to stadial foraminifera.

PAGE 17

6 Methane and the Stable Isotopic Comp osition of Benthic Foraminifera The flux of methane into the water colum n, and eventually the atmosphere, would be much greater were it not for the bacter ial consumption of methane, which catalyzes inorganic methane oxidation. Methane that is migrating upward in the sedimentary column may be oxidized by either aer obic or anaerobic bacteria, known as methanotrophs, depending on the availability of free oxygen. Aerobi c methanotrophs are able to use methane as an energy source th rough the production of carbon dioxide; these organisms are found living within the pores of sediments and in the tissues of benthic fauna associated with cold seeps ( Cavagna et al., 1999 ). Alternatively, anaerobic methanotrophs interact with another mi crobial group, the hydr ogen-oxidizing-sulfatereducers, in order to drive the metabolic tr ansformation of methan e into bicarbonate (and sulfate into hydr ogen sulfide) ( DeLong, 2000 ). Another bacterial process occurs in the water column, where free-living methanotrophs oxidize methane; these organisms create carbon dioxide plumes, which when diluted w ith normal bottom waters can deplete the 13CDIC by 4.5‰ ( Aharon et al., 1992 ; LaRock et al., 1994 ). The production of bicarbonate due to th e activity of methanogens has a profound effect on the pore-water chemistry and possi bly the isotopic co mposition of benthic foraminifera. Studies have shown that fo raminifera found within seepage areas have more negative 13C signatures than foraminifera found within areas unaffected by seepage ( Sen Gupta and Aharon, 1994 ). For instance, fossil benthic foraminifera from venting sites in the Gulf of Me xico had anomalously depleted 13C values (as light as –3.6‰), whereas fossil benthic foraminife ra from non-seep sites displayed 13C values as heavy as 0.4 ‰ ( Sen Gupta and Aharon, 1994 ).

PAGE 18

7 Pore-water Chemistry, Vital Effects, and Foraminiferal Composition In addition to ambient pore-water chemis try, taxon-specific "vital" effects and microhabitat effects also influence the geoc hemistry of benthic foraminiferal test carbonate ( McCorkle et al., 1990 ). Vital effects, which are a result of physiological processes, can be divided into two categor ies: metabolic isotope effects and kinetic isotope effects. Metabolic e ffects result from the incorpora tion of respired, isotopically light carbon dioxide into the foraminiferal test, which results in a depletion of 13C in the test ( Grossman, 1987 ), whereas kinetic effects occur during periods of rapid chamber formation, when lighter isotopes of carbon a nd oxygen are preferentially incorporated ( McConnaughey, 1989 ). Microhabitat effects can be attributed to fo raminifera living within the sediment at specific depths, where variations in the pore-water DIC may influence the 13C of the test. For instance, infaunal taxa display consistently lower 13C values than epifaunal taxa. Additionally, deep-dwe lling species are consistently more depleted in 13C than either shallow infaunal species or epifaunal species as a result of the decrease in the 13C of pore-water DIC with sediment depth ( McCorkle et al., 1990 ). However, despite these recognized trends, for any partic ular species that displays a broad depth range within the sediment, the variability of 13C values is low, despite the depth at which the foraminiferan is found ( Rathburn et al., 1996 ). While it has been proposed that the isotopic uniformity within a given species results from microenvironments, food preferences, or growth within a narrow depth range, the influence of pore-water chemistry on the isotopic composition of fo raminiferal tests remains debatable ( Rathburn et al., 1996 ; 2000 ).

PAGE 19

8 Diagenesis In addition to influencing the isotopic composition of live foraminifera, pore water chemistry may alter the isotopic composition of fossil foraminifera through diagenesis; contamination by biogenic calcite or post mort em calcite overgrowths is another plausible explan ation for the negative 13C values observed in some fossil foraminifera. In marine settings, a consor tium of bacteria produces bicarbonate while oxidizing organic matter and methane. Producti on of bicarbonate is enhanced at seep settings, where large quantities of methane are able to support a large population of bacteria. Carbonate precipitation may be enhanced by the producti on of bicarbonate, which would drive the reaction Ca2+ + 2HCO3 CaCO3 + H2O + CO2 (1) to the right. Additionall y, carbonate precipita tion should be enhanced at the sulfate/methane boundary where localized anaerobic methane oxidation may produce a sharp increase in the alkalinity of the pore water ( Blair and Aller, 1995 ). Authigenic carbonate is present at Eel River and Monterey Bay seep sites ( Stakes et al., 1999 ; Rathburn et al., 2000 ; this study). Thin secti ons of authigenic carbonates from Monterey Bay often contained pyrite framboids encased in high-Mg calcite filling the chambers of the U. peregrina which are composed of low-Mg calcite ( Stakes et al., 1999 ). Pristine U. peregrina tests, however, were also found in a groundmass of highMg calcite ( Stakes et al., 1999 ). It is unknown whether fine-grained authigenic carbonates are being precipitated within the cham bers of fossil foraminifera in unlithified sediments, such as those analyzed for th is study. Although foraminifera designated for isotopic analysis are microscopically examin ed for calcite contamination and cleaned

PAGE 20

9 ultrasonically, this technique may not detect authigenic carbonate grains that may be present inside some of the chambers of the test. If authigenic carbonate was contaminating foraminiferal tests, carbon and oxygen isotopic compositions would be expected to be widely variable in a la rge population of analyzed foraminifera. The problem of diagenetic alteration can be approached through thermodynamics, by calculating saturation states In thermodynamic modeling the chemical analysis of water is used to calculate the distribution of aqueous species. Saturation Indices (SI) determine whether a mineral should dissolve or precipitate. A positive saturation index for a mineral indicates that the pore water is oversaturated with respect to that mineral and thermodynamically, precipitation is favored. A negative value indicates that the pore water is undersaturated and di ssolution of that mineral is thermodynamically favored. This technique assumes that the pore water composition has not changed from the time of deposition. With burial, however, the pore water should become in creasingly saturated with respect to calcite through the diag enetic pathway shown by reaction (1). Objective/Scope of Research The primary objectives of this study are tw ofold: (1) to determine whether benthic foraminifera reliably record modern and hi storic sites of methane and associated DIC venting from cold seeps and (2) to determine how this record may be manifested in the isotopic composition of the foraminifera. Wh ile investigating this broad objective, the following more specific que stions are addressed: 1. What is the relationshi p between the isotopic signature of foraminiferal carbonate and the isotopic signature of ambient pore-water in methane seep environments? What variations exist in the isotopi c signatures of individual species within and between different seep settings? How do the stable isotopic signatures of benthic foraminifera from cold methane seeps compare to those generated in non-seep environments?

PAGE 21

10 2. Does methane seepage create a distinct isotopic signature in benthic foraminiferal tests that may serve to map the extent and history of methane fluxes? If so, can isotopic signatur es of fossil benthic foraminifera be used to identify the longevity and the extent of venting? 3. Within a given methane seep environment, do different species of benthic foraminifera have different carbon isotopic compositions? Are isotopic differences enhanced between epifaunal and infaunal species in methane seep environments? Along with analyzing fossil benthic foramini feral tests, this study also examines live (stained) deep-sea benthic foraminifera to determine the relationship between methane release and test composition, isotopic va riability within a gi ven species, and the variations in test composition generate d by seep and non-seep environments. McCorkle et al. ( 1990 ) analyzed the isotopic com position of live foraminifera from both the Atlantic and Pacific Oceans. Their main objective, however, was to identify the relationship between microhabitats and the carbon isotopi c composition of forami niferal tests. One previous study published by Rathburn et al. ( 2000 ) researched the relationship between live foraminifera and methane seepage off the slope of the Eel River, California. However, the limited number of live fo raminiferal specimens, the lack of 13CDIC analyses, and the limited geographic coverage has left unanswered questions regarding methane release and foraminiferal test composition. Study Areas Monterey Bay Monterey Bay provides an ideal location to investigate methane release from cold seeps (Figure 1-1). The bay is underlain by th e Salinian block, which is an allochthonous granodiorite basement rock that has moved northward during the past 21 million years of activity along the San Andreas Fault ( Page, 1970 ). The Salinian granodiorite, along with the San Simeon block, are the two major tectonic provinces within the bay ( Greene et al.,

PAGE 22

11 1993 ). The Miocene Monterey Formation, whic h along with its equivalents, are organicrich marine sediments, the Late Miocen e Santa Cruz mudstone, and the MiocenePliocene Purisma sandstone crop out offshore and along canyon walls ( Greene et al., 1989 ). Numerous faults, including the San Gregorio and Monterey Bay Fault Zones, dissect the bay creating a dynamic envir onment characterized by fluid flow ( Orange et al., 1999 ). Cold seeps have been found both as isolated communities along these major faults ( Barry et al., 1996 ) or among isolated zones of active mud volcanism ( Martin et al., 1997 ). Pore-water analyses obtained from push cores located within the cold seeps revealed methane concentrations up to 841 M ( Barry et al., 1997 ). Figure 1-1. Map showing the lo cation of Monterey Bay cold seeps, including Clam Flats and Invertebrate Cliffs, which were sampled in this study (taken from http://www.mbari.org/benthic/coldseeploc.htm ). At present in Monterey Bay, there are no known exposures of clathrates; however, discrete cold seeps sampled in the bay c ontain gaseous hydrocarbons and high molecular

PAGE 23

12 weight aliphatic and aromatic hydrocarbons ( Lorenson et al., 2002 ). Since no clathrates have been detected in Monterey Bay, fluid fl ow is instead likely th e result of tectonic compression, with interstitial fluids migra ting upward in the sedimentary column along faults ( Lorenson et. al, 2002 ). The methane seeping from Monterey Bay is likely to come from one of two sources. The organic-rich Monterey Form ation provides a thermogenic source for the methane ( Martin et al., 1997 ; Stakes et al., 1999 ), whereas the micr obial reduction of carbon dioxide below the sulfate reducti on zone provides a biologic source. Stakes et al. ( 1999 ) proposed that biological communities appear to be related to a deep source of reduced carbon, rather than a surficial sour ce, based on the spatial arrangement of the communities. The isotopic composition of most sites however, points to a mixed origin for the methane ( Martin et al., 1997 ). Eel River The Eel River Basin (Figure 1-2), which is part of a late Cenozoic forearc, extends approximately 210 km, from Cape Mendocino, California to Cape Sebastian, Oregon; the basin is bounded by the Cascad ia subduction zone to the west, and the Mendocino Fracture Zone to south ( Burger et al., 2002 ). The structural evolution of the basin continues today, as the convergence of the Gorda and North America plates continues; additionally, much of the deformation in the southern portion of the basin results from the continuing northward mi gration of the Mendocino Triple Junction ( Furlong and Govers, 1999 ). Although there are some similarities shar ed by Monterey Bay and the Eel River Basin, one major difference is the presence of gas hydrates in the Eel River Basin (Table 1-2). Kvenvolden and Field ( 1985 ) mapped the distribution of hydrates in the Eel River

PAGE 24

13 basin using the location of the bottom-simulating reflector (BSR). The BSR is a characteristic seismic reflection, which re sults from the strong impedance contrast between hydrate bearing sedime nts and gas-filled pore spac es. Although BSRs may also result from changes in acoustic velocity resu lting from diagenesis, the BSRs in the Eel River Basin are attributed to gas hydrates since they occur at the base of the gas hydrate stability field; additionally, the BSRs are f ound deeper in the sediment as water depth increases, which is characteristic of a gas hydrate, since diagenetic BSRs tend to become shallower as water depth increases ( Kvenvolden and Field, 1985 ). Additionally, the recovery of hydrates containing biogenic gas from shallow cores, less than 6 meters deep, taken from areas showing bottom-simulati ng reflectors confirms both the indirect geophysical evidence and the geologic observa tions, such as active methane venting from sediments, for the presence of gas hydrates in the basin ( Brooks et al., 1991 ). Figure 1-2. A map of the north ern California margin showing a portion of the Eel River Basin, which was sampled for this study. Adapted from Rathburn et al. (2000) Study area

PAGE 25

14 Table 1-2. Some of the sim ilarities and differences betw een the Monterey Bay and the Eel River basin. Monterey Bay Eel River Tectonics Right-lateral strike slip Convergent Foraminiferal Assemblages Similar to Eel River, with common species including U. peregrina and E. pacifica Similar to Monterey Bay, with common species including U. peregrina and E. pacifica Gas Hydrates None found Abundant Average Sedimentation Rate 2.2 mm/yr for Monterey Bay shelf* 4 mm/yr for Eel River shelf** Lewis et al (2002) ** Sommerfield and Nittrouer (1999)

PAGE 26

15 CHAPTER 2 METHODS Field Sampling Monterey Bay Samples from Monterey Bay were collected from two distinct sites during June of 2000. Samples from the first site were collected during Dive 1780 on June 22 from an area termed “Invertebrate Cliffs”, located at 3646.39N 1225.08W. These samples were gathered using the R.V. Point Lobos and ROV Ventana in a water depth of approximately 955 meters. Cores were taken from four distinct areas within Invertebrate Cliffs (Table 2-1); three of these sites were located within an area influenced by methane seepage, based on the presence of clam commun ities and bacterial mats. The seep areas sampled were a whitish-gray bacterial mat, a yellow bacterial mat, and a clam community; the area had a concentric arra ngement, with clams encircling the two bacterial communities (Figure 2-1). The last set of cores came from a reference site, which was located south of the clam community in an area of presumed non-seepage. Three push cores, which were 7 cm in diameter and up to 20 cm in length, were collected from each of the four sites for the analyses of foraminifera and pore water. Additionally, two hydraulic pist on cores, which were up to 45 cm in length, were taken for the analysis of fossil foraminifera; one co re was taken in the clam community, and the other core was taken between the two bacterial mats.

PAGE 27

16 Table 2-1. A listing of cores collected from Monterey Ba y and their designated use. DIVE SITE SITE DESRIPTION CORE DESIGNATED USE PC67 Live faunal analyses Whitish-gray bacterial mat PC34 Pore water geochemistry Yellow bacterial mat PC31* Pore water geochemistry Between the two bacterial matsHPC 2 Live faunal analyses PC30* Faunal analyses PC79* Pore water geochemistry 1780 Invertebrate Cliffs Clams HPC5* Faunal analyses (fossil) PC71 Live faunal analyses Reference (5 m N. of clam bed) PC38* Pore water geochemistry PC31* Live faunal analyses Clam bed PC80* Pore water geochemistry PC30 Live faunal analyses Bacterial mat PC28 Pore water geochemistry PC34 Live faunal analyses 1781 Clam Flats Reference (4 m. from Mat) PC72 Pore water geochemistry Results from these cores will be presented in detail in this thesis. Figure 2-1. A picture of the seepage area samp led from Invertebrate Cliffs located at approximately 955 meters water depth (Dive 1780). On June 23, a second area, Clam Flat s, located at 3644.7N 12216.6W, was sampled. During Dive 1781, cores were collected from a bacterial mat located at a water Whitegray bacterial Yellow bacterial mats Clams

PAGE 28

17 depth of approximately 1000 meters. Referen ce cores were collected four meters from the bacterial mats. Live clam beds, as well as a reference area located five meters due north of the clam bed were sampled. Once again, three push cores were taken from each site for isotopic and faunal an alyses (Table 2-1). A complete description of this site is provided by Barry et al. ( 1996 ). Eel River Eel River samples were collected August 21, 2001, during Dive 2052. Four distinct areas were visited for samp ling purposes: a bacterial mat (4047.058N 12435.729W), a clam bed (2 m north of 4047.080N 12435.700W, a site marked by active bubbling (4047.2001N 12435.7251W), and a reference area (4047.1717N 12435.6970W) (Table 2-2). The approximate water depth for all cores was 520 meters. Table 2-2. The location and desi gnated use of Eel River cores. DIVE SITE SITE DESCRIPTIONCORE DESIGNATED USE Long Core 5 Faunal analyses (fossil) Bacterial mat PC16 Pore water geochemistry Long Core 4 Faunal analyses (fossil) Clams PC8 Pore water geochemistry Long Core 2 Faunal analyses (fossil) 2052 Eel River Basin Bubble site PC19 Pore water geochemistry Foraminiferal Preparation and Analyses Live Foraminifera Preparation For all sites, push cores desi gnated for live foraminiferal analysis were vertically subsampled at 0.5-cm increments down to 3 cm and at 1-cm inte rvals down to 10 cm within the sediments. Fo llowing procedures outlined by Rathburn and Corliss ( 1994 ), each subsample was preserved in 200 ml of 4% buffered formaldehyde; in the laboratory 65 ml of Rose Bengal stain solution was adde d to foraminiferal samples and allowed to

PAGE 29

18 remain staining the samples for at least one w eek. Samples were then washed and sieved with nested 63 and 150 m mesh sieves. Stained bent hic foraminifera, which were believed to be alive at the time of collec tion, were then wet-picked from the >150 m fraction, sorted, and identified. As a convention in this paper, the use of the term “live” will refer to Rose Bengal stained (i.e., those foraminifera containing at least one stained chamber) foraminifera, which were presumed to be alive at the time of collection (Table 2-3). The term “fossil” will refer to thos e foraminifera subjected to the Rose Bengal stain, containing no stained chambers, which we re presumed to be dead at the time of collection. Additionally, all foraminifera co llected from cores not treated with Rose Bengal stain will be referred to as foss il (?), since it is unknown whether these foraminifera were alive or dead at the time of collection. Foraminifera are commonly found living up to 10 cm below the seafloor ( Jorrisen, 1999 ). In addition, Corliss ( 1985 ) found the deeper infaunal species Globobulimina pacifica which is tolerant to low oxyge n conditions, living at sediment depths down to 15 cm below the seafloor. Unless associated with a burrow, shallower infaunal foraminifera most likely are not living below 10 cm sediment depth. Live foraminifera from Monterey Bay were not found at high abundances below 5 cm sediment depth. All foraminifera designated for analysis were microscopically examined and cleaned using an ultrasonic bath. The Rose Bengal Staining Technique The Rose Bengal technique was first introduced in 1952 by Walton ; it is the most prevalent technique in the lite rature pertaining to the identif ication of live foraminifera. The stain functions by absorbing onto the surf ace of the protoplasm, staining it a bright

PAGE 30

19 red. As a result of the protoplasm filling the test and inhibiting the penetration of the stain, often only one or two of the newest chambers of the foraminifera are visibly stained ( Boltovskoy and Wright, 1976 ). Table 2-3. List of terms used in th is paper to describe foraminifera. Term Definition (as used in this paper) Live Those foraminifera subjected to the Ro se Bengal stain, which contain at least one brightly stained red or pink chamber. Believed to be alive at the time of collection (or at least recently) Fossil Those foraminifera subjected to th e Rose Bengal stain, which contain no stained chambers. Believed to be dead at the time of collection. Fossil (?) Those foraminifera not subjected to th e Rose Bengal stain, some of which, from the upper portion of the cores, c ould have been living at the time of collection. The manner in which Rose Bengal works has resulted in one of its major criticisms: since the stain adheres to protei ns, any algae or nematode occupying a fossil foraminiferal test will also be visibly stained. Additionally, even after death, the protoplasm may still absorb stain; however, the time required for the disintegration of protoplasm appears short in oxic environments ( Jorrisen, 1999 ). In anoxic environments, however, the degradation of th e protoplasm can take weeks or months and theoretically tens of years and could adsorb the Rose Bengal stain during this period ( Bernhard, 1988 ; Corliss and Emerson, 1990 ). Notwithstanding these restrict ions, Rose Bengal is the most practical technique available for dealing with larg e quantities of foraminifera ( Rathburn et al., 2000 ). Additionally, since the technique is commonly used, data are available for comparison. Finally, unlike other stains, it is known that Rose Bengal does not affect the isotopic signature of the foraminifera.

PAGE 31

20 Fossil Foraminifera Preparation Hydraulic piston cores and long cores desi gnated for fossil foraminiferal analyses were vertically subsampled at 1-cm interval s. In the laborator y, the subsamples were sonicated (if necessary), washed a nd wet-sieved using nested 63 and 125 m mesh sieves. Samples were washed onto filter paper and dried in the oven at 60C. The >125 m fraction designated for picking wa s split using a microsplitter (if the sample needed to be reduced into a manageable volume) and weighed. The foraminifera were then picked, counted, and identified. Foraminiferal Isotope Analyses All foraminifera, stained and unstained, us ed for isotopic analyses were stripped of organic matter by soaking in 15% hydrogen peroxide for 20 minutes; this procedure was followed by a methanol rinse. Live foraminifera had been sonicated following identification, however, fossil (?) foraminifera had not been previously sonicated and therefore to remove debris, fossil (?) foramini fera were sonicated in methanol (following the removal of hydrogen peroxide). Due to di fferences in the strengths of the tests, Epistominella pacifica, Bulimina mexicana, and Globobulimina pacifica were sonicated for 3 minutes at 30% power, while Uvigerina peregrina was sonicated at full power for 2 minutes. Following the methanol rinse, fossil (?) G. pacifica were broken to aid in removing debris from within the test; they were then cleaned using water and a finetipped paint brush. Fossil (?) G. pacifica was the only species analyzed where debris could be seen within the test, perhaps due to the transparency of the test walls. All samples were dried in the oven at 60 C.

PAGE 32

21 The foraminifera were reacted at 73 C with anhydrous phosphoric acid in a Kiel III device connected to a Finnigan MAT 252 isotope ratio mass spectrometer. The purpose of the Kiel device is to limit th e number of specimens required for accurate analyses, which aids in determining the isot opic variation within individual species. Foraminifera were analyzed for both 13C and 18O, whenever a sufficient number of specimens were present to generate enough gas for the mass spectrometer. Typically, enough gas was liberated when at least 20 g of foraminiferal tests were used, which corresponded to between one and six test s per analysis, depending upon the species analyzed. Whenever possible single tests we re analyzed to better assess variability within a species. With very large specimens of U. peregrina or G. pacifica tests had to be broken in half. Data is reported in the standard delta notation relative to the Pee Dee Belemnite (PDB) standard. The precision, ba sed on analyzing repli cates of the NBS-19 standard, averaged 0.04 ‰ for 18O and 0.08‰ for C. Pore-water DIC Analysis Carbon Isotopes Standards were prepared in order to dete rmine both the accuracy and precision of the pore-water DIC extraction technique. Tw o standards, with concentrations of 400 g/g KHCO3 and 750 g/g KHCO3, were prepared. The KHCO3 was analyzed as a solid and yields a 13C value of –23.91‰. One standard was ex tracted for every five samples, with the concentration of the sta ndard used altern ating between 400 g/g and 750 g/g KHCO3. The 13C of the standards averaged –23.370.20 ‰ (1 ). Sample data have been corrected for the offset between the solid and dissolved standards.

PAGE 33

22 Pore-water samples designated fo r carbon isotopic analyses ( 13C) were injected and stored in pre-evacuated vacutainers. Five milliliters of standard solution (either 400 g/g or 750 g/g KHCO3) was injected into pre-evacuated vacutainers. Prior to analysis, the samples and standards were acidified with approximately 100 L of concentrated H3PO4 to reduce the pH. The carbon dioxide, which evolved from the acidified porewaters, was extracted from the vacutainer s by puncturing the septum with a hypodermic needle attached to a vacuum line ( Martin et al., 1997 ). The gas, which is cryogenically cleaned of contaminants, was stored in 5-mm glass tubes, which were flame-sealed. The gas was then analyzed for 13C using an automatic cracker system attached to a VG Prism II mass spectrometer. Pore Water Solutes Analyses of pore water solutes, excludi ng DIC, were performed on board of the ship. Pore fluids were separated from th e sediments using cent rifugation. Chemical analyses were performed for the following c onstituents: alkalinity, sulfate, sulfide, calcium, magnesium, ammonium, ph osphate, silicate, and nitrate. The chemical analyses performed on board followed the methods used aboard the JOIDES Resolution ( Gieskes et al., 1991 ). SEM Analysis Selected specimens of Epistominella pacifica and Uvigerina peregrina were taken from Monterey Bay and Eel River sites. The purpose of the SEM analysis was to determine whether any recrystallization or ove rgrowths could be seen on the outside of the tests. Samples were chosen from thr ee general depths within the core (whenever

PAGE 34

23 possible): near the sediment-water interface, the middle of the core, and the bottom of the core (Table 2-4). Foraminifera were mounted onto stubs us ing double-sided tape. Prior to SEM analysis, the stubs were coated with a thin layer of a gold-palladium film, designed to make the samples conduct elect ricity and minimize the build up of charge on the surface of the test. The foraminifera were an alyzed using a JSM 6400 SEM at the Major Analytical Instrumentation Center (MAIC) at th e University of Florida. Two pictures of each specimen were taken: an overall view of the test and a close-up of the test. Table 2-4. Foraminifera used for SEM analysis. SITE CORE SPECIES DEPTH STATUS 0.5 16.5 Epistominella pacifica 27.5 15.5 21.5 1780 HPC5 Uvigerina peregrina 29.5 Fossil (?) 1780 PC30 Uvigerina peregrina 0.5 Monterey BayInvertebrate Cliffs 1780 PC67 Epistominella smithi 0.5 Live 0.5 15.5 Monterey Bay-Clam Flats 1780 HPC5 Uvigerina peregrina 24.5 Fossil (?) Eel RiverBubble Site Long Core 2 Epistominella pacifica 10.5 1.5 11.5 Epistominella pacifica 18.5 12.5 Eel RiverClam Bed Long Core 4 Uvigerina peregrina 17.5 Fossil (?) 0.5 Epistominella pacifica 12.5 1.5 15.5 Eel River Bacterial Mat Long Core 5 Uvigerina peregrina 25.5 Fossil (?) Eel River Reference Site Long Core 1 Epistominella pacifica 4.5 Fossil (?)

PAGE 35

24 CHAPTER 3 RESULTS Pore Fluid Geochemistry Monterey Bay Pore water chemistry is distinctly diffe rent in the two clam beds sampled: Invertebrate Cliffs (1780 PC 79) and Cl am Flats (1781 PC 80) (Appendix A). For instance, the calcium concentrations at Inverteb rate Cliffs show virtually no change down core, whereas the calcium concentrations at Clam Flats show variation with sediment depth, decreasing more than 4 mM in the first 8 cm of the core (Figure 3-1). The Clam Flats site also has significantly higher sulfide concentrations, with pore water values at Clam Flats being up to 118 times higher than In vertebrate Cliffs (Figure 3-2). There are also similar differences between the cores’ al kalinity gradients. Changes in sulfide and alkalinity likely correspond to sulfate re duction in the sediment (Figure 3-3). The carbon isotopic compositions also differ between the dive sites. The 13CDIC value from Clam Flats is approximately seven times lighter in the first centimeter of the core than the 13CDIC of Invertebrate Cliffs. The DIC fr om Invertebrate Cliffs is found to be no lighter than –9‰ in the 12 cm of pore water analyzed, whereas Clam Flats 13CDIC remains lighter than -40‰ from 2 cm on to th e bottom of the core (16 cm) (Figure 3-4). Oxidation of marine organic carbon ( 13CDIC of -25‰) cannot account for the isotopically light DIC found at Clam Flats. Although no bottom waters were collected from the

PAGE 36

25 dives, supernatant fluid was extracted from the tops of cores designated for pore water analyses and analyzed for 13CDIC (Table 3-1). 0 5 10 15 20 6789101112 1780 PC79 1781 PC80Depth (cmbsf) Ca (mM) Figure 3-1. Pore water calcium profiles fo r Monterey Bay clam beds (Dive 1780 PC79, Invertebrate Cliffs and Dive 1781 PC80, Clam Flats). 0 5 10 15 20 05101520 1780 PC79 1781 PC80Depth (cmbsf) HS(mM) Figure 3-2. Pore water sulfide (HS-) profiles for Monterey Bay clam beds (Dive 1780 PC79, Invertebrate Cliffs a nd Dive 1781 PC80, Clam Flats).

PAGE 37

26 0 5 10 15 20 0510152025303540 1780 PC79 1781 PC80Depth (cmbsf) Alkalinity (mM) Figure 3-3. Pore water alka linity profiles from Monterey Bay clam beds (Dive 1780 PC79, Invertebrate Cliffs a nd Dive 1781 PC80, Clam Flats). 0 5 10 15 20 -50-40-30-20-100 1781 PC 80 1780 PC 79Depth (cmbsf) Figure 3-4. The 13CDIC profile of pore water from Mont erey Bay clam beds (Dive 1780 PC79, Invertebrate Cliffs and 1781 PC80, Clam Flats). 13C DIC ( ‰ PDB )

PAGE 38

27 Table 3-1. The 13CDIC values of supernatant fluids taken from the tops of cores designated for pore water analyses. Location Dive numberCoreSite Description 13CDIC value (‰) 1780 PC31Yellow bacterial mat-3.72 Monterey Bay 1781 PC38Reference (clam bed)-3.93 2052 PC8 Clam bed -5.72 Eel River Basin 2052 PC16Bacterial mat -5.18 Eel River The various sites sampled from Eel Rive r: a bacterial mat, a clam bed, and a bubble site, all exhibit similar pore water tren ds (Appendix A). For example, all of the Eel River cores reveal an overall decrease in calcium concentration with depth, with approximately similar gradients (Figure 3-5). All cores display similar bisulfide ion and sulfate trends, although gradients differ; the bisulfide ion concentr ation increase more rapidly with depth for PC19 (the bubble site ) than for either PC8 (clams) or PC16, a bacterial mat (Figure 3-6). The bubble site al so has the steepest decreasing gradient for sulfate, with complete consumption of sulf ate by 10.5 cm (Figure 3-7). Additionally, all cores have an increase in alkalinity with de pth (Figure 3-8). The clam bed (PC8) and the bacterial mat (PC16) have similar 13CDIC gradients, with both cores having coretop supernatant fluid 13CDIC values of approximately -5‰ (Figure 3-9, Table 3-1). The bubble site (PC19) has initially lighter 13CDIC values, with a value of approximately -18‰ at 0.5 cm sediment depth. Within th e top five centimeter s of the core the 13CDIC values begin to be lighter than that of oxidized marine organic carbon (~ -22‰) (Figure 3-9).

PAGE 39

28 0 5 10 15 20 024681012 2052 PC16 2052 PC8 2052 PC19 Depth (cmbsf)Ca (mM) Figure 3-5. Calcium pore water profiles for Ee l River Dive 2052: PC16 (bacterial mat), PC8 (clam bed), and PC19 (bubble site). 0 5 10 15 20 05101520 2052 PC16 2052 PC8 2052 PC19Depth (cmbsf)HS(mM) Figure 3-6. Pore water sulfide profiles for Eel River Dive 2052: PC16 (bacterial mat), PC 8 (clam bed) and PC19 (bubble site).

PAGE 40

29 0 5 10 15 20 051015202530 2052 PC16 2052 PC8 2052 PC19Depth (cmbsf)SO4 (mM) Figure 3-7. Sulfate ion pore water profiles from Eel River Dive 2052: PC16 (bacterial mat), PC 8 (clam bed) and PC19 (bubble site). 0 5 10 15 20 0510152025303540 2052 PC16 2052 PC8 2052 PC19Depth (cmbsf)Alkalinity (mM) Figure 3-8. Pore water alka linities for Eel River Dive 2052: PC8 (clam bed), PC16 (bacterial mat), and PC19 (bubble site).

PAGE 41

30 0 5 10 15 20 -40-35-30-25-20-15-10-50 2052 PC 16 2052 PC 8 2052 PC 19Depth (cmbsf) d 13 C Figure 3-9. Pore water 13CDIC for Eel River Dive 2052 PC16 (bacterial mat), PC8 (clam bed) and PC19 (bubble site). Stable Isotopic Signatures of Foraminiferal Carbonate Monterey Bay Carbon isotopes The foraminifera from Invertebra te Cliffs display a range of 13C values (Table 32, Appendix B). Sediments at the Invertebra te Cliffs clam bed (1780 PC30) contain live U. peregrina with 13C values ranging from -0.04 to 0.85 ‰, over the entire length of the core, while the 13C of fossil (?) U. peregrina from HPC5 (Invertebrate Cliffs clam bed) varies from 0.01 to -1.05 ‰ (Figure 3-10). Additionally, when the 13C values of individual live U. peregrina from within the same depth in terval are compared, variations up to 0.55 ‰ are observed at 0.5 cm and 4.5 cm. A smaller range of 13C values is evident in other species; for instance, live specimens of E. pacifica range from –0.50 to 13C DIC ( ‰ PDB )

PAGE 42

31 –0.79 ‰ over the length of the core, PC30, whereas fossil (?) E. pacifica from HPC5 vary between –0.13 to –1.16 ‰ over the entire length of the core (Figure 3-11). Live B. mexicana range between –0.70 and –0.92 ‰ within PC 30 and fossil (?) specimens from HPC5 vary between –0.52 and –1.04 ‰ (Figur e 3-12). Most species of fossil (?) foraminifera have a wider carbon isotopic rang e compared to their living counterparts. G. pacifica is the only species sampled from Invertebrate Cliffs where live 13C values have a broader range compared to fossil (?) 13C values (Figure 3-13). For most species from Invertebrate Cliffs, however, the num ber of fossil (?) tests analyzed greatly surpasses the number of live te sts analyzed, possibly contribu ting to the greater variation in the fossil (?) isotopic composition relativ e to the live composition (Table 3-2). Table 3-2. A statistical comparison of Monterey Bay foraminifera Dive No./ Core No. Species Status n Mean 13C ( 13C) Min (‰) Max (‰) Mean 18O ( 18O) Min (‰) Max (‰) Live 9-0.800.08 -0.92-0.703.28 0.04 3.2 3.36 Fossil 1-0.83N/A N/AN/A3.33 N/A N/AN/A B. mexicana Fossil (?)*17-0.750.16 -1.04-0.523.47 0.24 3.053.94 Live 12-0.650.10 -0.79-.50 3.18 0.07 3.093.30 E. pacifica Fossil (?)*70-0.450.15 -1.16-0.133.28 0.17 2.313.60 Live 27-0.500.18 -0.85-0.043.06 0.18 2.593.40 Fossil 2-0.800.21 -0.95-0.653.13 0.10 3.063.20 U. peregrina Fossil (?)*33-0.590.29 -1.050.013.25 0.13 3.063.73 Live 25-1.380.48 -2.23-0.413.32 0.07 3.233.49 1780 PC30 G. pacifica Fossil (?)*24-1.040.22 -1.69-0.613.40 0.11 3.263.71 Live 3-1.090.07 -1.17-1.033.44 0.31 3.223.80 B. mexicana Fossil 5-1.430.48 -2.24-1.044.74 0.09 4.654.89 Live 4-0.960.04 -0.98-0.924.25 0.73 3.154.66 E. pacifica Fossil 4-1.150.06 -1.20-1.094.61 0.03 4.594.65 Live 37-0.910.45 -2.05-0.103.20 0.16 3.044.04 U. peregrina Fossil 15-1.410.31 -2.03-1.034.65 0.10 4.494.83 1781 PC31 G. pacifica Live 3-3.970.54 -4.56-3.493.30 0.11 3.203.42 *Indicates foraminifera are from 1780 HPC5. **Statistical analyses were unavailable as only one isotopic value was obtained fo r these specific foraminifera.

PAGE 43

32 No systematic variations in the carbon isotopic patterns can be discerned for Invertebrate Cliffs (Dive 1780 PC30). Isotopi c values fluctuate randomly, but generally remain around the same isotopic values throughout the le ngth of the core. 0 5 10 15 20 25 30 35 -2.5-2-1.5-1-0.500.5 PC30 U. peregrina (live) PC30 U. peregrina (fossil) HPC5 U. peregrina (fossil (?))Depth (cmbsf) Figure 3-10. Dive 1780 HPC5 and PC30 (Invertebrate Cliffs clam bed) Uvigerina peregrina 13C vs. depth. 0 5 10 15 20 25 30 35 -2.5-2-1.5-1-0.500.5 PC30 E. pacifica (live) HPC5 E. pacifica (fossil (?))Depth (cmbsf) Figure 3-11. Dive 1780 HPC5 and PC30 (Invertebrate Cliffs clam bed) Epistominella pacifica 13C vs. depth. 13C ( ‰ PDB ) 13C ( ‰ PDB )

PAGE 44

33 13C ( ‰ PDB ) 0 5 10 15 20 25 30 35 -2.5-2-1.5-1-0.500.5 PC30 B. mexicana (live) PC30 B. mexicana (fossil) HPC5 B. mexicana (fossil (?))Depth (cmbsf) Figure 3-12. Dive 1780 HPC5 and PC30 (Invertebrate Cliffs clam bed): Bulimina mexicana 13C vs. depth. 0 5 10 15 20 25 30 35 -2.5-2-1.5-1-0.500.5 PC30 G. pacifica (live) HPC5 G. pacifica (fossil (?))Depth (cmbsf)d13C Figure 3-13. Dive 1780 (Invertebrate Cliffs clam bed) HPC5 and PC30 Globobulimina pacifica 13C vs. depth. 13C ( ‰ PDB )

PAGE 45

34 Variable carbon isotope values are also observed at the Clam Flats site (Dive 1781 PC31), with the 13C of live U. peregrina ranging from –0.10 to –2.05‰ (Figure 314); this large variation is obs erved between individuals with in the same depth interval (2-2.5 cm). The carbon isotopic range of fossil U. peregrina is smaller than the range found for live specimens, with values lying between –1.03 and –2.03 ‰. U. peregrina is the most abundant species of foraminifera from Clam Flats; however, the 13C of other foraminiferal species at the Clam Flats si te used for comparison purposes with other cores is presented (Figure 3-15). These ot her species, including the shallow infaunal species E. pacifica and B. mexicana fall within the range of values found for U. peregrina Live E. pacifica varies between –0.92 and –0.98 ‰, while fossil specimens of E. pacifica range from –1.09 to –1.20 ‰. Live B. mexicana vary from –1.03 to –1.17 ‰, while their fossil conspecifics vary be tween –1.04 and –2.24 ‰ over the length of the core. The isotopic values of live G. pacifica a deeper infaunal species, which vary between –3.49 and –4.56 ‰, is slightly li ghter than values obtained from U. peregrina The last species presented, Planulina species which is an epifaunal foraminiferan, has carbon isotopic values ranging between –0.22 and +0.45 ‰, which is slightly heavier than most of U. peregrina’s isotopic values. From the data available, there is no syst ematic variation in carbon isotopes with depth for PC31 (Clam Flats). No discernibl e disparities exist between live and fossil conspecifics. When looking at the length of the core, fossil U. peregrina fall within the isotopic range found for live U. peregrina (Figure 3-14). Both E. pacifica and B. mexicana also have similar ranges for live and fo ssil conspecifics over the length of the core (Figure 3-15).

PAGE 46

35 0 1 2 3 4 5 -2.5-2-1.5-1-0.50 U. peregrina (live) U. peregrina (fossil)Depth (cmbsf)d13C Figure 3-14. Dive 1781 PC31 (Clam Flats clam bed) Uvigerina peregrina 13C vs. depth 0 1 2 3 4 5 -5-4-3-2-101 B. mexicana (fossil) B. mexicana (live) G. pacifica (live) E. pacifica (fossil) E. pacifica (live) Planulina species (live)Depth (cmbsf) d13C Figure 3-15. Dive 1781 PC31 Clam Flats (clam bed): Epistominella pacifica Bulimina mexicana Globobulimina pacifica and Planulina species 13C vs. depth. 13C ( ‰ PDB ) 13 C (‰ PDB )

PAGE 47

36 Oxygen isotopes Oxygen isotopes also vary for a given sp ecies of benthic foraminifera; however, similar to carbon isotopes, no down-core trends occur. E. pacifica and B. mexicana from 1780 PC30 (Invertebrate Cliffs) both have a sl ightly larger variation in fossil (?) 18O than in live 18O (Figure 3-16, 3-17). U. peregrina was the only species analyzed from 1780 PC30 that has greater 18O variability for live specimens compared to fossil (?) specimens (Figure 3-18). Live G. pacifica which shows the la rgest variation in 13C ( = 0.54 ‰) has a relatively narrow range of 18O values, varying up to 0.22 ‰ within 1780 PC30 (Figure 3-19). The oxygen isotopes do not vary appreciably from live to fossil conspecifics found at the same depth w ithin the core (Figures 3-16, 3-17, 3-18, and 3-19). When live and fossil foraminifera from Cl am Flats are compared to each other, they have for the most part different 18O signatures (Table 3-2, Figure 3-20). For the entire core, the average 18O value for fossil U. peregrina (n=15) is 4.65 0.10 ‰. Alternatively, the live U. peregrina (n=37) have a mean of 3.20 0.16 ‰ over the length of PC31. Unlike these differences in 18O, the carbon isotopic va lues for live and fossil U. peregrina show some overlap in value, even though mean 13C values are lighter for fossil specimens (Table 3-2, Figure 3-15). Sim ilar offsets are seen in other species from Clam Flats (1781 PC31) (Table 3-2). Eel River Carbon isotopes No live foraminiferal data are availabl e from Eel River, however fossil (?) foraminifera were analyzed for all Eel Ri ver sites (Appendix B). Long core 5, which

PAGE 48

37 0 5 10 15 20 25 30 35 22.533.544.5 PC30 E. pacifica (live) HPC5 E. pacifica (fossil (?))Depth (cmbsf)d 18 O Figure 3-16. Dive 1780 HPC 5 and PC30 (Invertebrate Cliffs clam bed) Epistominella pacifica 18O vs. depth. 0 5 10 15 20 25 30 35 22.533.544.5 PC30 B. mexicana (live) PC30 B. mexicana (fossil) HPC5 B. mexicana (fossil (?))Depth (cmbsf) Figure 3-17. Dive 1780 HPC5 and PC30 (Invertebrate Cliffs clam bed) Bulimina mexicana 18O vs. depth. 18O ( ‰ PDB ) 18O ( ‰ PDB )

PAGE 49

38 0 5 10 15 20 25 30 35 22.533.544.5 PC30 U. peregrina (live) PC30 U. peregrina (fossil) HPC5 U. peregrina (fossil (?))Depth (cmbsf)d18O Figure 3-18. Dive 1780 (Invertebrate Cliffs clam bed) HPC5 and PC30: Uvigerina peregrina 18O vs. depth. 0 5 10 15 20 25 30 35 22.533.544.5 PC30 G. pacifica (live) HPC5 G. pacifica (fossil (?))Depth (cmbsf)d18O Figure 3-19. Dive 1780 (Invertebrate Cliffs clam bed) HPC5 and PC30 Globobulimina pacifica 18O vs. depth. 18O ( ‰ PDB ) 18O ( ‰ PDB )

PAGE 50

39 0 1 2 3 4 5 33.544.555.5 U. peregrina (live) U. peregrina (fossil)Depth (cmbsf)d18O Figure 3-20. Dive 1781 PC31 (Clam Flats clam bed) Uvigerina peregrina 18O vs. depth. was collected from a bacterial mat, contains fossil (?) U. peregrina that have a mean 13C value of –1.49 2.10 ‰ (Table 3-3, Figure 3-21) If, however, three of the outlying values are excluded, specifically – 4.48, -6.97 and –11.59‰, the mean 13C value increases to –0.93 0.28‰. Fossil (?) E. pacifica isotope values range from –1.01 to –0.32 ‰ (Figure 3-21). The other two cores, Long core 4 and Long core 2 contain foraminifera with extreme ranges in 13C values. For instance, Long core 4, which was taken in a clam bed, contains U. peregrina specimens with 13C values ranging from –0.46 to –7.13‰ (Figure 3-22). Even more extreme, the 13C of E. pacifica ranges from –0.65 to –19.46 ‰, with the lightest of values occurring rather sh allowly at 1.5 cm. However, the majority of the foraminifera from Long core 4 have a 13C value of 18O ( ‰ PDB )

PAGE 51

40 approximately 2‰ or heavier (Figure 3-22). In contrast, Long core 2 (from the bubble site) has more variable 13C values than LC4 (Figure 3-23). For example, out of a sample set that includes 33 U. peregrina data points, the range in 13C values is from –0.65 to –23.22‰ (Figure 3-23), with a mean 13C of –6.70‰, and a standard deviation ( ) of 7.00‰ (Table 3-3). B. mexicana and E. pacifica show similar variability. The variation in 13C for all cores is unsystematic with depth. Table 3-3. A statistical comparison of foss il (?) foraminifera from Eel River Basin. Dive Number and Core Number Species n Mean 13C ( 13C) Min (‰) Max (‰) Mean 18O ( 18O) Min (‰) Max (‰) U. peregrina 33 -6.707.00 -23.22-0.653.60 0.61 2.144.76 E. pacifica 18 -3.464.99 -15.24-0.163.36 0.46 2.764.03 2052 Long Core 2 B. mexicana 15 -12.736.12 -21.13-0.714.05 0.19 3.834.51 U. peregrina 32 -1.371.55 -7.13-0.463.56 0.34 2.814.05 2052 Long Core 4 E. pacifica 20 -2.944.52 -19.46-0.653.70 0.28 3.084.30 U. peregrina 36 -1.492.10 -11.59-0.413.70 0.17 2.993.97 2052 Long Core 5 E. pacifica 17 -0.750.20 -1.01-0.323.67 0.14 3.373.97 Oxygen isotopes Variable 18O values accompany the wide range of 13C values for Eel River cores. The bubble site (LC2), which has the most variable 13C values, also has the widest range of 18O values, ranging from 2.14 to 4.76‰ throughout the core (Figure 324, Table 3-3). The majority of foraminiferal 18O values from long core 4 (clams) are between 3 and 4‰ (Figure 3-25); likewise, the majority of foraminifera from long core 5 (bacterial mat) have 18O values between 3.5 and 3.9‰ (Figure 3-26). No down core trends in variability could be distingu ished for any of the Eel River cores.

PAGE 52

41 0 5 10 15 20 25 30 -12-10-8-6-4-20 U. peregrina (fossil (?)) E. pacifica (fossil (?))Depth (cmbsf) Figure 3-21. Dive 2052 long core 5 (bacterial mat): Uvigerina peregrina and Epistominella pacifica 13C vs. depth. 0 5 10 15 20 -20-15-10-50 E. pacifica (fossil (?)) U. peregrina (fossil (?))Depth (cmbsf) Figure 3-22. Dive 2052 Long core 4 (clam bed): Epistominella pacifica and Uvigerina peregrina 13C vs. depth. 13C ( ‰ PDB ) 13C ( ‰ PDB )

PAGE 53

42 0 5 10 15 20 -25-20-15-10-50 U. peregrina (fossil (?)) E. pacifica (fossil (?)) B. mexicana (fossil (?))Depth (cmbsf) Figure 3-23. Dive 2052 Long core 2 (bubble site): Uvigerina peregrina Epistominella pacifica and Bulimina mexicana 13C vs. depth. 0 5 10 15 20 22.533.544.55 U. peregrina (fossil (?)) E. pacifica (fossil (?)) B. mexicana (fossil (?))Depth (cmbsf) Figure 3-24. Dive 2052 long core 2 (bubble site): Uvigerina peregrina Bulimina mexicana and Epistominella pacifica 18O vs. depth. 13C ( ‰ PDB ) 18O ( ‰ PDB )

PAGE 54

43 0 5 10 15 20 22.533.544.55 E. pacifica (fossil (?)) U. peregrina (fossil (?))Depth (cmbsf) Figure 3-25. Dive 2052 long core 4 (clam bed): Epistominella pacifica and Uvigerina peregrina 18O vs. depth. 0 5 10 15 20 25 30 22.533.544.55 U. peregrina (fossil (?)) E. pacifica (fossil (?))Depth (cmbsf) Figure 3-26. Dive 2052 Long Core 5 (bacterial mat): Uvigerina peregrina and Epistominella pacifica 18O vs. depth. 18O ( PDB ) 18O ( PDB )

PAGE 55

44 Scanning Electron Microscope (SEM) Micrographs No evidence of recrystallization or over growths is visible fr om the micrographs taken from Monterey Bay’s Invertebrate Cl iffs or Clam Flats (Appendix C, Figure 3-28 and Figure 3-29). This observation was cons istent with the isot opic composition of the foraminifera, which did not have un usually light carbon signatures. Some of the foraminifera photographed from Eel River appear to be diagenetically altered (Appendix C, Figure 330). The photographed specimens are from 2052 long core 4, the clam bed, however, it is likely other Eel River cores also contain recrystallized foraminifera or foraminifera containing authigenic carbonate, based on the light carbon isotopic signatures pr esent in some foraminifera.

PAGE 56

45 (b) Figure 3-27 (a, b). A scanni ng electron micrograph of an Uvigerina peregrina from Monterey Bay’s Invertebrate Cliffs clam be d. This specimen was taken from 21-22 cm and was not cleaned before analys is. (a) An overall shot of th e test. (b) A close up of the test from the region identified in (a). (a)

PAGE 57

46 Figure 3-28. A scanning electron micrograph of an Epistominella pacifica from Monterey Bay’s Invertebrate Cliffs clam be d. Specimen was taken from 27-28 cm depth. Specimen was cleaned before analysis. (a). An overall view of the test. (b). A close-up of the test from the region identified in (a). (a). (b).

PAGE 58

47 Figure 3-29 (a,b). A scanni ng electron micrograph of a U. peregrina from Eel River’s long core 4 (clam bed). Specimen was taken fr om 8-9 cm depth and was cleaned prior to analysis. (a) An overall view of the test. (b ). A close-up of the re gion identified in (a). (a) (b).

PAGE 59

48 CHAPTER 4 DISCUSSION Although cold seep locations and foramini feral distributions are well documented, previous research reporting the isotopic com positions of seep foraminifera is scarce. Previous studies have shown that seep-inhabiting foraminifera have no special adaptations that enable them to inhabit seep sites ( Bernhard et al., 2001 ), where sulfide and methane concentrations can reach potenti ally toxic levels. Some seep inhabiting species, however, do appear to have variable carbon is otopic values ( Sen Gupta et al., 1997 ; Rathburn et al., 2000 ); pore water was not collected during either of these prior studies ( Sen Gupta et al., 1997 ; Rathburn et al., 2000 ), so the relationship between pore water 13CDIC and the 13C of foraminiferal carbonate was not analyzed. The Effects of Methane on Pore Water Composition The DIC in pore waters is a mixture of th ree end-members: seawater DIC, which has a 13C approximating 0‰ PDB, oxidized organic matter ( 13C = -25‰), and oxidized methane, which has 13C values typically between –25 and -50‰ ( Whiticar, 1999 ). The relative amounts of marine organic matter oxidation and seawater present in the subsurface will influence the pore water com position; if enough seawater is present within the sediments, it could increase the 13CDIC enough to conceal an isotopically light methane signature. Pore water composition is altered by the activity of clams, which intensify the downward mixing of relatively h eavy seawater and pore water, leading to a

PAGE 60

49 heavier 13CDIC signature. For example, in dense Calyptogena clam beds, the flux of seawater resulting from bioirrigation caused by bivalves was found to exceed the upward advection of pore fluids by several orders of magnitude at Aleutian cold seeps ( Wallman et al., 1997 ). Bacterial activity occurring within th e sediment will also alter pore water composition. For instance, the microbial br eakdown of organic matter, by a reaction similar to: 2CH2O + SO4 2HCO3 + H2S, (2) will result in increased alkalinity and increased sulfide concentrations within pore waters. Bicarbonate produced from the microbial reduction of or ganic matter would yield 13C values of approximately –25 ‰. In additi on to the above reaction, anaerobic methane oxidation often occurs at cold s eep environments and also leads to increases in alkalinity. Anaerobic methane oxidation consumes sulf ate and methane by the net reaction: CH4 + SO4 2HCO3 + HS+ H2O (3) ( Reeburgh, 1976 ). Since bicarbonate is a product, and the dominant component of the DIC at a neutral pH, the 13CDIC should record the isotopical ly light carbon signature inherited from the methane. The Invertebrate Cliffs clam bed ( 1780 PC30) shows little indication of the occurrence of methane oxidation, based on 13CDIC, alkalinity, and bisulfide ion profiles. Pore water 13CDIC values are heavier than -8.6‰ in the upper 12 cm of the sediment column, and sulfide and alkali nity profiles show virtually no changes over the length of the core, with values remaining around 1 mM and 3 mM, respectively. Alternatively, pore waters at Clam Flats show light 13CDIC values, high alkalinity and downcore

PAGE 61

50 increases in sulfide. The presence of 13C values less than -25‰ confirms the presence of methane and its subsequent oxidation in the pore water. The differences in the pore water compos itions at Invertebrate Cliffs and Clam Flats could have a variety of causes. For in stance, the Invertebrate Cliffs clam bed may have lower seepage rates or if seepage is episodic, it is possible that seepage had occurred more recently at Clam Flats, leading to is otopically lighter DIC and increased alkalinity and sulfide concentrations compared to Invert ebrate Cliffs. Additionally, higher rates of bioirrigation could mask the isotopically light seep signature of I nvertebrate Cliffs. Furthermore, a different methane source (pos sibly more thermogenic methane, which is isotopically heavier than bi ogenic methane), could account for some of the disparity between the two sites. Most likely, however, it is a combination of these processes that may have masked the isotopically light methane signature of the Invertebrate Cliffs seep. Like the Clam Flats clam bed, all of the Eel River cores show a down core increase in alkalinity coupled with an incr ease in sulfide. The mixing of bicarbonate from marine organic carbon and the bicarbonate in seawater cannot ac count for the light 13C displayed by the pore water from the Eel River cores, which decrease below -25‰ (Figure 3-9). Methane oxidation must be occurring in the subsurface. In addition, the microbial activity responsible for methane and organic matter oxidation, which increase alkalinity, could initiate the pr ecipitation of authigenic carb onate; this could explain the decreasing calcium concentrations with sediment depth. Pore Water, Methane, and the Isotopic Composition of Foraminiferal Tests The carbon isotopic composition of foraminife ra differs from that which would be produced by direct precipitation from solution due to the processes of biogenic carbonate

PAGE 62

51 formation. These differences between ab iotic carbonate formation and biogenic carbonate formation are genera lly characterized as “vital effects”. According to Grossman ( 1987 ), the source for most foraminife ral carbonate is inorganic carbonoxygen compounds; however, isotopically light carbon-oxygen compounds resulting from both metabolic activities within the or ganism, as well as organic matter, may also contribute to calcificat ion of the test ( Grossman, 1987 ). Foraminifera inhabiting seep sites would, at least periodi cally, be inhabiting isotopically light pore waters, depending on the relative contributions of methane oxi dation, sea water DIC, and marine organic matter. The heterogeneous nature of methane rel ease along with variations in the timing of test calcification could create intrasp ecific isotopic variati ons in foraminiferal carbonate. For instance, the Gr een Canyon area in the Gulf of Mexico displays a wide range of conspecific foraminiferal 13C values compared to non-seep areas. However, Rose Bengal stained foraminifera at this site are sparse (i.e., most individuals were dead at the time of collection), therefore only unsta ined tests were analyzed. These tests may have been influenced by diagenetic processes. Sen Gupta and Aharon ( 1994 ) report variations up to 1.9 ‰ in the carbon isotopic composition of unstained U. peregrina from the upper centimeter of a core at a Gulf of Mexico hydrocarbon seep. Diagenesis as a Contributing Factor to Iso topically Light Foraminiferal Carbonate Although methane appears to create variab ility in the carbon isotopic composition of foraminifera, it does not appear to expl ain the negative isotopic excursions seen in some fossil foraminifera. Other factors, su ch as diagenesis, may have influenced the isotopic composition of these foraminifera. Depending upon the composition (and the

PAGE 63

52 saturation state) of the pore fluids, fossil fora minifera could either be recrystallized or become sites of authigenic carbonate precipit ation. This would not only create variability in fossil foraminiferal tests, but would also create more negative carbon isotopic compositions, since these carbonates would be in isotopic equilibrium with pore fluids, unlike the foraminiferal carbonate precipitate d during the life of the foraminifera. Instead of hydrate destabilization, which was the theory proposed by Kennett et al ( 2000 ) to explain variations in foraminifera l test carbonate during the Pleistocene, Stott et al. ( 2002 ) proposed that in the modern Santa Barbara Basin, changes in the flux and oxidation of organic carbon asso ciated with variations in productivity and habitat depth generate variation in th e isotopic composition of live benthic foraminifera. The 13C of pore waters sampled were isot opically heavier than –18 ‰ in the upper 4.2 meters of sediment at the Santa Barb ara basin center and slightly heavier at the basin slope ( Stott et al., 2002 ). These pore water values show little evidence of an influence by methane, which today enters the basin through cold seep environments ( Stott et al., 2002 ). Foraminifera inhabiting these pore waters, specifically Buliminella tenuata an infaunal foraminifera, had carbon is otopic values that approximated pore water 13CDIC values at 3 to 4 mm, which is where they are believed to calcify their tests ( Stott et al., 2002 ); carbon isotopic values for B. tenuata were around –3 ‰ ( Stott et al., 2002 ). Stott et al. ( 2000 ) reported that increases in the ra tes of carbon oxidation led to a –1.5 ‰ shift in the average 13C of B. tenuata between the early 1900s and the 1960s. Because today these foraminifera seem to accurately record pore water 13CDIC, Stott et al. ( 2002 ) suggested that as productivity in the North Pacific varied due to climatic

PAGE 64

53 changes during the Pleistocene, so did the pore water 13C and the foraminiferal carbonate values. This theory may be appli cable to non-seep sites in the modern Santa Barbara Basin; however, no seep sites were sampled to determine the isotopic variability of Santa Barbara seep foraminifera. Diagenesis was also listed as a possible contributing factor to the negative carbon isotopic compositions of Pleistocene foramini fera from the Santa Barbara basin, which Kennett et al. ( 2000 ) found to vary up to 5‰ between stadials and interstadials. Reimers et al. ( 1996 ) found that the pore waters become supe rsaturated with respect to calcite below 2 cm, which could affect the down core carbonate record th rough secondary calcite precipitation. For this study, although foraminiferal test s were microscopically examined for evidence of diagenesis before analysis, au thigenic carbonate grains could have been present within the chambers of some of the tests. Many diagenetic processes may influence fossil tests. For instance, the bact erial decomposition of biological tissue, such as the protoplasm of foraminifera, unde r anoxic conditions generates ammonia and carbon dioxide, which lead to increased alkalinity ( Berner, 1980 ). Additionally, if the bacterial reduction of sulfate is occurring within the sediment, alkalinity will increase further. As a consequence of these reacti ons, the degree of saturation with respect to carbonate minerals does increase. Depending on the degree of satura tion, specifically whether supersaturation is reached, authigenic carbonate may be precip itated. This initial carbonate precipitation may function as a nucle us for continued growth, assuming that supersaturation is maintained ( Berner, 1980 ).

PAGE 65

54 The bacterial decomposition of the protoplasm, however, is probably more important for the formation of authigenic ir on minerals, such as pyrite, because of the production of sulfide resulting from the reduction of sulfate, than for authigenic carbonate formation ( Berner, 1980 ). Iron is probably readily available in the reducing pore waters and siliciclastic sediments of the seeps. Some of the authigenic carbonates from Monterey Bay analyzed by Stakes et al. ( 1999 ) contained fossil foraminifera whose chambers were concentrically filled with pyrite framboids encased in high-Mg calcite. However, pyrite formation is not solely associ ated with diagenetic processes, as it may also form in the tests of live foraminifera due to anaerobic bacterial activity occurring within the organism ( Seigle, 1973 ). Diagenesis in the Eel River Basin Methane seepage alone cannot account for all of the isotopic variability seen in Eel River basin foraminifera. The fossil (?) foraminifera from Eel River sites had carbon isotopic compositions up to 21.3‰ lighter than Monterey Bay foraminifera and oxygen compositions, which were heavier than Mont erey Bay by up to 0.72‰; this excludes the fossil foraminifera from Clam Flats, which ha d, in general, heavier oxygen isotopes than Eel River foraminifera (Table 4-1). Table 4-1. A comparison of the mean 13C and 18O values of U. peregrina from Invertebrate Cliffs (1780 PC30), Clam Fl ats (1781 PC31), and Eel River (2052 LC2, LC4, and LC5). Dive and Core No. Site Description Mean 13C ( 13C)Mean 18O ( 18O) 1780 PC30 (fossil ?) Clam bed -0.59 0.29 3.25 0.13 1781 PC31 (fossil) Clam bed -1.41 0.31 4.65 0.10 2052 LC 2 (fossil ?) Bubble site -6.70 7.00 3.60 0.61 2052 LC 4 (fossil ?) Clam bed -1.37 1.55 3.56 0.34 2052 LC 5 (fossil ?) Bacterial mat -1.30 1.91 3.70 0.17

PAGE 66

55 Using the geochemical modeling program PHREEQC ( Parkhurst and Appelo, 1999 ), saturation indices were calculated for th e Eel River cores; due to the lack of necessary parameters (such as pH, magnesium, or sulfate), saturation states could not be calculated for Monterey Bay. PHREEQC is a computer program that is designed to perform a wide variety of low-temperature aqueous geochemical calculations including speciation and saturationindex calculations ( Parkhurst and Appelo, 1999). There are, however, a couple of problems encountered when using PHREEQC for seawater calculations. First, PHREEQC uses an i onic-strength term in the Debye Hckel expressions in an attempt to extend the limit of applicability of this model for seawater ionic strengths (~ 0.7 molal); the applicability of the model may fail if ionic strengths are high (> ~1.0 molal) ( Parkhurst and Appelo, 1999). Another problem encountered with the calculations is the inabil ity to introduce pressure as a variable in the modeling, which could have an effect on mineral formati on at water depths of 500 to 1000 meters. The bubble site (PC19) was characterized by the most positive saturation indices compared with the other Eel River sites, w ith dolomite more oversaturated compared to calcite or aragonite (Figure 4-1). Long core 2, which contains foraminifera from the bubble site, also had the most variable foraminiferal carbon values, with 13C values ranging from .22 to .49. The saturation i ndices calculated for long core 4 (clam bed) were also all positive, with dolomite being the most oversaturated, with saturation indices up to 2.42, followed by calc ite, then aragonite (Figure 42). The first sample of long core 5 (bacterial mat), 0.5 cm, was unders aturated with respect to calcite and aragonite. However, all depths below 0.5 cm were oversaturated with respect to dolomite, calcite, and aragonite (Figure 4-3).

PAGE 67

56 0 2 4 6 8 10 12 14 00.511.522.533.5 Aragonite Calcite DolomiteDepth (cmbsf)Saturation Index (SI) Figure 4-1. A plot of the sa turation indices (SI) versus de pth for the bubble site (PC19, which corresponds to the foraminifera from long core 2). 0 1 2 3 4 5 6 7 00.511.522.5 Aragonite Calcite DolomiteDepth (cmbsf)Saturation Index (SI) Figure 4-2. A plot of the sa turation indices (SI) versus depth for PC8 (clam bed, which corresponds to the foraminifera from long core 4).

PAGE 68

57 0 5 10 15 20 -0.500.511.522.53 Aragonite Calcite DolomiteDepth (cmbsf)Saturation Index (SI) Figure 4-3. A plot of the sa turation indices (SI) versus depth for PC16 (bacterial mat, which corresponds to the foraminifera from long core 5). Based on the values and the ranges of is otopes (carbon and oxygen) seen in fossil (?) foraminifera from Eel River and the mode l-predicted saturation indices, it is likely that secondary calcite precipitation is masking variability created by methane seepage. If venting is episodic, during times of cessation of seepage the saturati on of pore fluids is likely to change from that of supersaturat ed to saturated (and po ssibly undersaturated), which would cause authigenic car bonate precipitation to either cease or in the case of undersaturation, could cause dissolution to o ccur. However, when seepage does begin, the composition of pore fluids will once again be altered based on the relative amounts of DIC contributed by seawater, organic ma tter oxidation, and methane oxidation. If supersaturation occurs, precipitation will pref erentially occur on foraminifera, which had prior mineral growth, leading to increased vari ation in isotopic composition. In this way variations as large as those seen in Long core 2, where at the most extreme 13C values

PAGE 69

58 reach –23.22 ‰ at 9.5 cm depth and just a centimeter below this a U. peregrina has a 13C signature of –1.05 ‰, can be generated. Although saturation states were not calcu lated for Monterey Bay, based upon the isotopic composition of the foraminifera, it is unlikely that diagenesis is affecting the fossil foraminifera. In addition to no forami nifera having extremely light isotopes, such as those seen in Eel River, the standard deviations for both carbon and oxygen isotopes are relatively small (Table 3-2), wi th maximum standard deviations ( ) of 0.48 and 0.29, for 13C and 18O, respectively. If diagenesis were occurring, standard deviations should be larger, due to variations in pore flui d composition and the possibility of multiple periods of precipitation. Considering that live foraminifera from Monterey Bay, which would not be affected by diagenetic processe s, have larger standard deviations, (a maximum of 0.55 for 13C and 0.73 for 18O), it further negate s the presence of diagenesis at these sites. Stable Isotopic Compositions The Variation in Foraminiferal Carbon Isotopes Data focusing on the conspecific variati on in foraminiferal carbonate isotopes are limited, particularly within active seep envir onments. Within non-seep environments, the carbon isotopic composition of most species of foraminifera varies little downcore, despite changes in the isotopi c composition of pore water ( McCorkle et al., 1997 ). Live U. peregrina from two non-seep sites, the Nort h Carolina margin and the California margin (south of Pt. Sur), were analyzed and found to have 13C variations less than 0.5‰ over the length of a core ( McCorkle et al., 1997 ). Accompanying pore water 13CDIC values for these cores, which were 14.5 cm or shorter, ranged from 1.10 to

PAGE 70

59 –3.43‰ ( McCorkle et al., 1997 ). A slightly larger variation was seen in G. pacifica which is characterized as a deeper infaunal species, compared to U. peregrina ; Live G. pacifica displayed 13C variations up to 0.98‰ in pore waters with 13CDIC ranging between –0.32 and –2.54‰ ( McCorkle et al., 1997 ). However, live G. pacifica from the California borderlands, a low-oxygen envi ronment, showed less variation in 13C downcore, with an intrasp ecies variation of 0.28‰ ( Mackensen and Douglas, 1989 ). Fossil G. pacifica from the California borderlands show ed slightly more variability in 13C than live specimens, with variations up to 0.33‰ over 8-cm ( Mackensen and Douglas, 1989 ). No accompanying pore water data was available. The lack of intraspecific va riation at non-seep sites has been attributed to growth within a narrow depth range growth within microenvi ronments characterized by relatively constant 13C values and food preferences ( McCorkle et al., 1990 ; 1997 ; Rathburn et al., 1996 ). Most individuals within a core would have a similar test composition if growth took place within a sp ecific microenvironment during short-lived episodes, such as during an in crease in food availability ( McCorkle et al., 1997 ). At Clam Flats, foraminifera found liv ing at the same depth had isotopic compositions that differed by as much as 1.95‰. These differences imply either that calcification occurred during significantly different por e water conditions for the foraminifera for at least a portion of their te sts, perhaps in different microenvironments, or that variations in the am ounts of metabolic carbon dioxide incorporated into the test may be causing variation in test 13C values. These two factors could be linked; a larger amount of bacteria would be sustained dur ing times of increased methane seepage, leading to isotopically lighter pore water DIC. In additi on, deposit-feeding foraminifera,

PAGE 71

60 such as U. peregrina and G. pacifica are known to ingest a larg e amount of sediment, as well as algal cells, bacteria, and organic detritus ( Goldstein, 1999 ). Bacteria in particular seem to comprise an important role in th e diet of depositfeeding foraminifera ( Goldstein and Corliss, 1994 ). Growth should be encouraged during these times of increased food availability, leading to varia tions in test composition not only by the occasional ingestion of bacteria, which oxidize isot opically light methane, but al so by the incorporation of isotopically light DIC from th e pore waters. This woul d, however, likely decrease isotopic variability because all foramini fera would end up with light isotopic compositions if the majority of grow th occurred under these conditions. Variations in foraminiferal car bonate among different species could be enhanced by methane seepage due to increased variations in pore water 13C with depth. The interspecific variation in the isotopic composition of forami nifera is much larger than the intraspecific variation. Fractionation linke d to growth rate may account for some of the interspecies variation ( McCorkle et al., 1997 ), with sporadic gr owth occurring during times of increased bacterial activity related to methane release. However, differences in the isotopic composition between species of fora minifera have verified that microhabitat (environmental) effects influence the carbon is otopic composition of benthic foraminifera ( McCorkle et al., 1990 ; 1997 ). Variations in 13C values up to 3 or 4‰ have been documented between species of benthic fora minifera living within the same core simultaneously ( McCorkle et al., 1990 ; 1997 ; Rathburn et al., 1996 ). These disparities were enhanced at seep sites, where deeper in faunal taxa were subjec ted to more depleted pore waters compared to shallow in faunal and epifaunal species.

PAGE 72

61 The difference in the 13C composition between epifaunal and deep infaunal species of foraminifera from sout h of Pt. Sur varies up to 1.68‰ ( McCorkle et al., 1997 ). The epifaunal species, Cibicidoides wuellerstorfi had 13C values ranging from –0.01 to –0.20‰, compared to shallow infaunal Uvigerina species which ranged from –0.49 to –0.97‰, and the deep infaunal species, G. pacifica which had 13C values between –1.34 and –1.67‰ ( McCorkle et al., 1997 ). Epifaunal species at Clam Flats, such as Planulina have 13C values ranging from –0.22 to +0.45‰, compared to the shallow infaunal species, U. peregrina which ranges from –0.10 to –2.05‰, and G. pacifica a deep infaunal species, which has 13C values ranging from –3.49 to –4.56‰. The maximum variation seen between infaunal a nd epifaunal species at Clam Flats was 5.01‰, compared to 1.68‰ for the non-seep site south of Pt. Sur. This increased variation is likely a result of the isotopically light 13CDIC found at seep sites, which influences the infaunal forami nifera to a larger extent. The Relationship between Methane, Pore Water 13C, and Foraminiferal Carbonate The oxidation of methane produces bicarbonate that retains methane’s isotopically light carbon signature. Foramini fera, which primarily use inorganic oxygencarbon compounds ( Grossman, 1987 ) to calcify their tests, could incorporate this bicarbonate into their tests preserving the s ource’s signature. However, when comparing two Monterey Bay seep sites, th e Clam Flats site and the Inve rtebrate Cliffs site, isotopic differences are not as large as expected base d on the differences in the values of pore water 13CDIC at these sites. Pore waters at Clam Flats were characterized by isotopically lighter DIC than at Invertebra te Cliffs (Figure 3-4). Live U. peregrina from Invertebrate Cliffs range in 13C values from -0.04 to -0.85‰. Live U. peregrina from Clam Flats,

PAGE 73

62 where 13C DIC values were four to six times light er than at Invertebrate Cliffs, range from –0.1 to –2.05‰, only approximately 2 times li ghter than Invertebra te Cliffs. Other species of foraminifera, specifically live E. pacifica and live B. mexicana inhabiting both sites had mean 13C values that were more depleted (by ~0.30‰) at Clam Flats relative to Invertebrate Cliffs. In all cas es, although foraminifera from th e site with the isotopically lighter DIC had isotopically light er tests (Table 4-2), the isot opic differences were not the magnitude expected based upon prior fossil bent hic foraminiferal analyses. Even though the foraminifera appear to respond to and in corporate a portion of the isotopically light DIC into their tests, a more significant portion of foraminifera l carbonate must come from other carbon-bearing compounds. Table 4-2. A comparison of the mean 13C values and standard deviations of live foraminifera from Clam Flats (PC31) and Invertebrate Cliffs (PC30). Invertebrate Cliffs 1780 PC30 Clam Flats 1781 PC31 Species Mean 13C Mean 13C U. peregrina -0.50 0.18 -0.91 0.45 E pacifica -0.68 0.10 -0.98 0.04 B mexicana -0.80 0.08 -1.09 0.07 G. pacifica -1.39 0.49 -3.97 0.55 It would be expected that deep infaunal species, such as G. pacifica would be influenced by more isotopically depleted por e waters compared to shallow infaunal taxa, such as U. peregrina As is the case in non-seep sites ( McCorkle et al., 1990 ; 1997 ), this expectation appears to be true for seep sites as well; the 13C of G. pacifica from both sites is isotopically lighter than U. peregrina The isotopic values of live G. pacifica at Invertebrate Cliffs had average 13C values of –1.11‰ and –1.40‰ compared to live G.

PAGE 74

63 pacifica from the same depths (2.25 cm a nd 4.5 cm) at Clam Flats, which had 13C values of –3.49‰ and –4.56‰. A Comparison of the Isotopic Compositio n of Seep and Non-seep Foraminifera A comparison of foraminifera from known seep sites, with very different pore water chemistries did not create the carbon is otopic differences expected based on prior fossil foraminifera research. Howeve r, much of this early research ( Wefer et al., 1994 ; Dickens et al., 1995 ; Kennett et al., 2000 ) was looking at older fossil foraminifera, i.e., some from the Pleistocene, where it is uns ure what type of environment was present when these foraminifera were alive. The sites sampled for this study, however, are from true seep sites, where evidence of seepage, such as bubbling, authigenic carbonate crusts and chimneys, and cold seep communities, such as clams and bacterial mats, are present. Nonetheless, the seep sites have differe nt isotopic compositions compared to nonseep sites. For instance, from cores in the Atlantic and the Pacific Oceans, McCorkle et al. ( 1990 ) collected data confirming a shallow infaunal habitat for U. peregrina Additionally, the 13C of U. peregrina was found to be nearly equal to the 13CDIC from the top few millimeters of the cores, values typically between –0.6 and –1.2‰ ( McCorkle et al., 1990 ). At Clam Flats live U. peregrina have 13C values no lighter than –2.05‰ although the 13CDIC of pore water at 0.5 cm sediment depth was -36‰. In addition, even Invertebrate Cliffs, which at present shows little sign of methane seepage, has a pore water 13CDIC value of –4.78‰ at 0.5 cm sediment depth compared to live U. peregrina isotope values no lighter than –0.85‰. McCorkle et al. ( 1990 ; 1997 ) and Rathburn et al. ( 1996 ) determined that in order to compare living foraminifera from different regions, the 13C DIC of bottom water (b.w.)

PAGE 75

64 must be subtracted from the foraminiferal 13C value, yielding a value termed 13C. Actual bottom water samples were not collect ed during dives for this study; however, the supernatant fluid from the core t ops was removed and analyzed for 13CDIC. The supernatant fluid has 13CDIC values that range from –3.72 to –6.42‰ (Table 3-1), which could indicate that methane oxidation is occu rring in the water column above seeps at Monterey Bay and Eel River sites. An alte rnative explanation for the isotopically light values of supernatant is that diffusion or advection of isotopically light DIC from the sediments could enrich the water in 12C. Nonetheless, methanotrophic activity does occur above seep sites in the Eel River basin and b acteria seem to oxidize methane soon after it is released from the sediment ( Valentine et al., 2001 ). Bottom water 13CDIC values (collected 0.5 m above active seeps) ranged from –2.26 to –4.53‰ for cold seeps in the Gulf of Mexico ( Aharon et al., 1992 ); these values are similar to the supernatant values repor ted here, indicating the supernatant values could represent bottom water values. Water samples were collected using a rosette, deployed from the deck of the R/V Atlant is II, containing remote–tripping water sampling bottles ( Aharon et al., 1992 ). In contrast, bottom wa ter values reported from non-seep sites in the Pacific Ocean south of Pt. Sur varied from –0.19 to –0.29‰ at the two locations sampled ( McCorkle et al., 1997 ). Bottom water samples were collected using small Niskin bottles mounted on the corner of a box corer; the bottles were engineered to close when the corer reached the seafloor ( McCorkle et al., 1997 ). Since there are few studies (of seep and nonseep sites) reporting both pore water and foraminiferal isotopic data, U. peregrina is the species for which the most data is available, among both prior research and this study; therefore it wi ll be the only species

PAGE 76

65 whose isotopic data is substituted into the equation for 13C. In addition, because bottom water was not sampled for this study, when determining the value of 13C, both estimated values of bottom water and valu es obtained using supernatant fluid are compared for the Eel River and Monterey Bay cores. Although no supernatant fluid was analyzed for the Invertebrate Cliffs or the Clam Flats clam beds, supernatant fluid is av ailable from other environments sampled at these sites. At Invertebra te Cliffs, supernatant fluid was analyzed from the yellow bacterial mat (located within the clam ring (Figure 2-1)); the fluid has a 13CDIC value of –3.72‰, whereas supernatant fluid from a referen ce site at the Clam Flats clam bed has a 13CDIC value of –3.93‰. If these two values ar e substituted for bottom water in the equation for 13C, resulting values for U. peregrina are approximately 3‰ heavier than values reported from other sites (Figure 4-4a). All U. peregrina show enrichment in 13C relative to the supernatant DI C. If, however, an estimated bottom water value of –0.3‰ is used, the 13C values of the U. peregrina fall mostly within the range of reported values, where U. peregrina are depleted in 13C relative to bottom water DIC (Figure 44b). Still, the variation in th e carbon isotopi c composition of U. peregrina from methane seeps at Monterey Bay is greater than that reported from non-seep sites. Supernatant fluid for Eel River cores has 13CDIC values of -5.18 and -5.72‰ (Table 3-1), which contrasts mark edly with estimated bottom water 13C values based on Geosecs data, which Rathburn et al. ( 2000 ) report to be about –0.58‰ for the Eel River basin. When the 13CDIC values of the supernatant flui d from Eel River (Long Core (LC) 4 and LC 5) were substituted for bottom water and compared to U. peregrina carbon isotopic compositions, 13C values varied significantly from those reported in the

PAGE 77

66 literature. All U. peregrina had a positive 13C (Figure 4-5a); the values were approximately between 1.75 and 6‰, compared to those reported in the literature, which range from approximately –0.25 to -2‰ ( McCorkle et al., 1990 ; 1997 ; Rathburn et al., 2000 ). The fossil U. peregrina from Clam bed 4, which had an average 13C that is significantly lighter than those reported in the literature (a s well as a much larger standard deviation), were determined to be the result of authig enic carbonate contamination ( Rathburn et al., 2000 ). When LC 4 and LC5 were replotted using the bottom water 13CDIC value (-0.58 ‰) estimated by Rathburn et al ( 2000 ) for their sampling site (40 47.08N, 124 35.68W), which is near the location of this study’s sampling area, the average 13C values are in good agreement with those reported in the literature (Figure 4-5b). Fossil (?) U. peregrina from LC4 and LC5 have much larger st andard deviations than all cores for which data is available, except fossil U. peregrina from clam bed 4. The Eel River cores analyzed contain some foraminifera, which have been diagenetically altered, based on pore water saturation states, isotopic compositions, and comparison to other seep and non-seep sites. The maximum standard deviation for all species of foraminifera is 7.00‰. This value is larger than the excursions documented by Dickens et al. ( 1995 ) who document a –2 to -3‰ shift in 13C and 18O values in benthic foraminifera during the Paleocene, or th e -5‰ excursions during the Quaternary documented by Wefer et al. ( 1994 ) and Kennett et al. ( 2000 ) off the coast of Peru and in the Santa Barbara Basin, respectively. Th ese large excursions may also include a diagenetic component. The findings from this study show that the relationship between methane and the 13C of foraminifera is not characteri zed by large excursions. Instead,

PAGE 78

67 (a). (b). foraminifera from seepage sites have more variable carbon isotopic compositions, which are similar to or approximately a mil or two lighter than foraminifera inhabiting non-seep sites. -1012341780 PC30 (fossil) 1780 PC30 (fossil (?)) 1780 PC30 (live) 1781 PC31 (fossil) 1781 PC31 (live) Clam bed 5 (live) Clam bed 5 (fossil) Clam bed 4 (live) PSII-BC207 (live) PSII-BC213 (live) -1.5-1-0.500.51780 PC30 (fossil) 1780 PC30 (fossil (?)) 1780 PC30 (live) 1781 PC31 (fossil) 1781 PC31 (live) Clam bed 5 (live) Clam bed 5 (fossil) Clam bed 4 (live) PSII-BC207 (live) PSII-BC213 (live)d13C Figure 4-4(a, b). The average 13C and standard deviation ( ) of U. peregrina from Invertebrate Cliffs (1780 PC30) and Clam Flats (1781 PC31) compared to values reported in the literature. (a). Actual bottom water 13C is not used; instead, the supernatant fluid from the core tops is substituted for bottom water (See text for discussion). Clam bed 5 and Clam bed 4 are seep sites in the Eel River Basin sampled by Rathburn et al ( 2000 ). PSII cores are non-seep sites off the coast of California, south of Pt. Sur ( McCorkle et al., 1997 ). (b). An estimated bottom water value of –0.3‰ is used for the calculation of the average 13C from Clam Flats and Inve rtebrate Cliffs. Note the difference in the scale of the x-axis from (a). 13C ( 13C – 13C b.w.) (‰ PDB) 13C ( 13C – 13C b.w.) (‰ PDB)

PAGE 79

68 (b). -10-8-6-4-20246CH90-BC5 (live) CH90-BC4 (live) PSII-BC207 (live) PSII-BC213 (live) Clam bed 5 (live) Clam bed 5 (fossil) Clam bed 4 (live) Clam bed 4 (fossil) LC4 (fossil (?)) LC5 (fossil (?)) -10-8-6-4-202CH90-BC5 (live) CH90-BC4 (live) PSII-BC207 (live) PSII-BC213 (live) Clam bed 5 (live) Clam bed 5 (fossil) Clam bed 4 (live) Clam bed 4 (fossil) LC4 (fossil (?)) LC5 (fossil (?)) Figure 4-5(a, b). The average 13C and standard deviation of U. peregrina from Eel River’s Long core (LC) 4 (clam bed) a nd LC5 (bacterial mat), compared to those reported in the literature. (a). LC4 and LC5 are plotted using 13CDIC values obtained from supernatant fluid (see text for discussion ). All PSII cores are from the Pacific Ocean south of Pt. Sur, whereas CH90 cores are take n from the North Carolina slope north of Cape Hatteras ( McCorkle et al., 1997 ). Clam bed 5 and Clam bed 4 cores were collected in the Eel River basin by Rathburn et al. ( 2000 ). (b) LC4 and LC5 are replotted using Rathburn et al.’s ( 2000 ) bottom water 13CDIC value of –0.58‰. 13C ( 13C – 13C b.w.) (‰ PDB) (a). 13C ( 13C – 13C b.w.) (‰ PDB)

PAGE 80

69 Foraminiferal 18O Compositions Within Clam Flats, fossil foraminifera consistently display 18O values that are approximately 1.5‰ heavier than live c onspecifics (Figure 4-6), whereas the 13C values of fossil species are less than 0.5‰ lighter than their live counte rparts (Figure 3-14, Figure 3-15). Only a few overlapping oxygen isotopic values are se en and could result from live specimens being inhabited by algae or nematodes, leading to a false ‘live’ designation. In addition, most of the live fora minifera have oxygen isotopic values that are similar to both live and fossil (?) fora minifera from Invertebrate Cliffs. 1 1.5 2 2.5 3 3.5 4 4.5 5 33.544.55 U.peregrina (live) U. peregrina (fossil) B. mexicana (fossil) B. mexicana (live) E. pacifica (fossil) E. pacifica (live) E. smithi (fossil) E. smithi (live)Depth (cmbsf) Figure 4-6. A 18O comparison of live and fossil cons pecific foraminifera from Clam Flats (1781 PC31). Note: E. pacifica values from 2.75 cm overlap and the live B. mexicana (from 4.5 cm) is clustered w ith other live species around 3.15‰. The 18O values of the fossil foraminifera fr om Clam Flats places them within the range of authigenic carbonate analyzed from the Clam Flats area, which Stakes et al. ( 1999 ) determined to vary between 4.05 and 5.19‰. The 13C values of these same 18 O(‰PDB )

PAGE 81

70 authigenic carbonates range from –48.82 to –52.60‰ ( Stakes et al., 1999 ). If authigenic carbonate overgrowths, such as those found by Stakes et al. ( 1999 ) were to account for the 1.5‰ increase in 18O, the resulting decrease in 13C would be between –13 and –18‰, as somewhere between 28 and 35% of the oxygen isotopic composition would have to be provided by authigenic carbonate Although pore fluid chemistry could have varied significantly over time, the isotopic co mposition of numerous fossil foraminifera (of various species) is consistent; therefore, it is unlikely that even multiple stages of authigenic carbonate formation could explain the disparity in 18O between live and fossil foraminifera. One explanation for the disparity between fossil and live foraminifera from Clam Flats is that the fossil foraminifera are remnants from a colder time, perhaps the Last Glacial Maximum (LGM), exposed by an erosional event. Barry et al. ( 1996 ) noted the Clam Flats site was characterized by clam s inhabiting small shallow depressions. Additionally, clams were noted to form aggr egations along the lower edges of small, meter-scale scarps ( Barry et al., 1996 ). As slumping occurs, foraminifera inhabiting the sediment will be displaced. With later recol onization of the site, live foraminifera would inhabit sediment containing older, fossilized foraminifera; these fossilized foraminifera could have secreted their te sts under very different te mperature conditions, perhaps during glacial times, when deep water was older and had lower 13C and cooler temperatures would have contributed to heavier 18O compositions. Furthermore, seawater 18O would have been heavier due to th e glacial sequesteri ng of isotopically light ice. According to Curry et al. ( 1988 ), the 18O of the deep water in the Pacific Ocean during the LGM was between 3.86 0.06‰ and 4.35 0.02 ‰. In addition, the

PAGE 82

71 oxygen isotopic difference between the LGM and present (expressed as glacial – interglacial) is between 1.33 and 1.67‰ ( Curry et al., 1988 ). Likewise, the LGM had deep-water 13C values that were between 0.21 and 0.60‰ lighter than present 13C values ( Curry et al., 1988 ). These offsets correlate nicely with the isotopic offsets between fossil and live foraminifera from Clam Flats. A Comparison of Foraminiferal Oxygen Iso topes from Seep and Non-seep Sites Living foraminifera from different areas can be compared if calcite in equilibrium with bottom water 18O values are subtracted from foraminiferal 18O values, yielding a value termed 18O ( McCorkle et al., 1990 ; 1997 ; Rathburn et al., 1996 ). For Monterey Bay, the value for calcite in equilibrium with bottom water 18O was taken from Stakes et al. ( 1999 ), who calculate a 18O value of approximately 3.2‰ for a temperature of 4 C, which is approximately the same bottom water temperature as this study. Living foraminifera from both Invert ebrate Cliffs and Clam Flats fall within the range of 18O values reported in the literature (Figure 47). In addition, foss il foraminifera from Invertebrate Cliffs also fall with in the reported ra nge, excluding two U. peregrina values. Fossil foraminifera from Clam Flats, however, fall outside th e reported range, with values varying from 1.29 to 1.63‰, providing further confirmation that these foraminifera secreted their tests under different bottom water conditions than live foraminifera inhabiting the same sediment. In the Eel River basin, sites sampled duri ng this study are close to and in similar water depths (~500 m) to those sampled by Rathburn et al. ( 2000 ), who estimated a bottom water 18O in equilibrium with calcite value of 2.35‰. The average 18O values for Eel River fossil foraminifera are heavier than the fossil values reported by Rathburn et

PAGE 83

72 -0.500.511.52 1780 PC30 (fossil ?) 1780 PC30 (live) 1781 PC31 (live) 1781 PC31 (fossil) PSII-BC207 (live) PSII-BC213 (live) Clam bed 5 (live) Clam bed 5 (fossil) Clam bed 4 (live) Clam bed 4 (fossil) Dd18O Figure 4-7. A plot of the 18O values of U. peregrina from Invertebrate Cliffs (1780 PC30) and Clam Flats (1781 PC31) relative to those values reported in the literature. PSII cores are from south of Pt. Sur ( McCorkle et al., 1997 ). Clam bed 5 and Clam bed 4 are from the Eel River Basin ( Rathburn et al., 2000 ). al. ( 2000 ) (Figure 4-8). In addition, many are heavier than the only 18O value reported for authigenic carbonate from the area, which had a 18O value of 3.79‰ and a 13C value of –33.57‰ ( Rathburn et al., 2000 ). It has been previously discussed that the isotopic variability found throughout the Eel River cores is in part due to diagenesis which is also masking variability caused by hydrate dissociation (and the subsequent bact erial oxidation of meth ane). Because Eel River sites sampled near the boundary of th e hydrate stability zone hydrate dissociation could be causing variations in the 18O of pore fluids. The lattice composing methane hydrates preferentially incorporates 18O, therefore, upon dissociation, fluids containing hydrates would be isotopically heavier than fluids not influenced by hydrate dissociation. For instance, Aharon et al. ( 2001 ) determined that methane hydrate dissociation has led to a maximum 18O enrichment of 1.7 ‰ in Bolivina species in the Gulf of Mexico. The timing of hydrate dissociation and test calcification could create isotopic variability, 18 O(‰PDB)

PAGE 84

73 however, because live foraminifera were not analyzed, determining the relative contribution of these processes is impossible. -0.500.511.52 2052 Long Core 5 (fossil ?) 2052 Long Core 4 (fossil ?) 2052 Long Core 2 (fossil ?) Clam bed 5 (live) Clam bed 5 (fossil) Clam bed 4 (live) Clam bed 4 (fossil) PSII-BC207 (live) PSII-BC213 (live) Dd18O Figure 4-8. A plot of the 18O values of U. peregrina from Eel River (2052) LC5 (bacterial mat), LC4 (clam bed) and LC2 (bubble s ite) relative to those values reported in the literature. PSII cores ar e from south of Pt. Sur ( McCorkle et al., 1997 ). Clam bed 5 and Clam bed 4 are from the Eel River Basin ( Rathburn et al., 2000 ). 18O (‰ PDB)

PAGE 85

74 CHAPTER 5 CONCLUSIONS Methane seepage and its ensuing oxidation by bacteria produces isotopically light DIC in pore waters. In addition, methanotroph ic activity creates a favorable environment for the precipitation of authigenic minerals; increases in alkalinity and sulfide could result in the precipitation of carbonate and iron minera ls, particularly pyrite. In addition, the degrading protoplasm of dead foraminifera may provide a nucleus for mineral growth ( Berner, 1980 ). Because seepage is likely episodic pore fluid saturation states could vary temporally, increasing the diversity of isotopi c signals found at seep sites. Therefore, careful attention needs to be paid to fossil benthic foraminifera being used to assess the history of methane seepage; as variation in the carbon isotopic composition will be overshadowed by diagenetic effects. Live foraminifera should be analyzed whenever possible to estimate the relative isotopic contribution of methan e seepage and possibly diagenesis to fossil foraminiferal carbonate. This study shows that methane seepage creates carbon isotopic variability in benthic foraminiferal tests; the negative carbon isotopic signal which is imparted on the test is not more than a few per mil. Foraminifera living in the 13C-depleted environment of seeps did not develop 13C values in their tests that were similar to pore water values, which had carbon isotopic valu es as light as -37‰ in th e upper 5 cm of a core. Therefore, although methane seepage does create steeper decreases in 13CDIC with depth than profiles containing organic matter oxi dation alone, isotopic differences between

PAGE 86

75 epifaunal and infaunal species are not enhan ced by more than 1 or 2‰ relative to nonseep species. Large negative carbon isotopi c excursions, like those seen in Eel River foraminifera, appear to result from authigen ic carbonate contamination; however, live foraminifera, which would help quantify the variability contributed by methane seepage, were not analyzed. Additional studies on the variability of foraminiferal carbon isotopes in seep and non-seep environments would enab le a more complete characterization of the effects of methane seepage on benthic foraminifera. Based on the available data from non-s eep environments, it appears that the carbon isotopic composition of benthic foraminifera from seep sites is similar or more negative than non-seep foraminifera. However, bottom water samples need to be collected and analyzed for 13CDIC to determine if the 13C equation can be used to compare seep and non-seep foraminifera. A dditionally, bottom water samples must be collected from seep sites to determine whether DIC values in the waters above seeps are as 13C depleted, up to –4.5‰, as those reported by Aharon et al. ( 1992 ). Looking at epifaunal foraminifera, such as Planulina species which are believed to secrete their test in isotopic equilibrium with bottom waters (at least in non-seep environments) would allow for a better characterization of bottom water chemistry and enable conclusions to be drawn on the ability of seep fluxes to alter bottom wa ter composition. Although a microhabitat effect does exis t in seep settings and pore water composition does influence benthic foraminiferal composition, it appears that pore water plays a larger role in creating isotopic va riability than it does in imparting negative isotopic signatures on foraminifera. For instance, in non-seep sites, U. peregrina had carbon isotopic compositions that were nearly equal to the pore water concentration in

PAGE 87

76 the upper 0.5 cm of the sediment ( McCorkle et al., 1997 ). This, however, was not the case for the seep environments sampled during this study; the 13C of U. peregrina on average, was between 4 and 18 times heavier than pore water 13CDIC. This disequilibrium could indicate th at the foraminifera have specific microenvironments where calcification takes place, possibly near the surface or near burrows where seawater DIC ( 13CDIC approximately 0‰) would contribu te more to the DIC pool. Sediments containing pore waters that ha ve isotopically lighter carbon signatures also contain foraminifera with more vari able carbon isotopic co mpositions. It is, however, impossible to know the pore water conditions under which these foraminifera calcify their tests. Nonetheless, foraminife ra are incorporating a portion of DIC derived carbon into their tests, which creates isot opic variability among foraminifera as pore water chemistry changes.

PAGE 88

77 APPENDIX A PORE WATER CHEMISTRY Dive Number Location Push Core No. cm-bsf Alkalinity (mM) pH Ca (mM) Mg (mM) SO4 (mM) HS(mM) 0.5 13.59 7.39 17.1 2.0 14.97 7.41 18.9 4.0 16.72 7.20 18.3 0.2 6.0 15.91 7.46 19.1 8.0 17.61 17.2 3.0 10.0 19.89 17.0 1.2 34 12.0 17.83 7.92 16.1 0.5 2.59 7.40 11.8 2.0 2.74 7.28 11.3 4.0 2.66 11.2 0.2 6.0 3.01 7.60 11.8 0.5 8.0 3.14 7.65 11.5 0.6 10.0 3.38 7.87 11.3 1.1 79 12.0 3.61 7.87 11.8 0.5 3.39 12.9 1.1 2.0 7.34 7.93 13.3 1.0 4.0 13.57 8.02 13.0 2.2 6.0 16.22 14.1 2.3 8.0 19.57 7.65 15.3 2.2 10.0 20.03 7.71 17.2 2.3 31 12.0 20.56 16.3 1.9 0.5 2.61 7.32 10.7 2.0 2.58 7.31 11.3 4.0 2.58 7.40 12.0 6.0 2.46 7.32 11.7 8.0 2.59 7.30 11.1 10.0 2.71 7.46 12.1 12.0 2.73 7.57 10.8 14.0 2.85 7.49 11.2 16.0 2.92 11.7 1780 Monterey Bay – Invertebrate Cliffs 38 18.0 3.01 7.49 11.2 0.5 11.10 11.2 4.3 2.0 19.47 10.3 7.9 1781 Monterey BayClam Flats 80 4.0 31.80 9.0 15.4

PAGE 89

78 Dive Number Location Push Core No. cm-bsf Alkalinity (mM) pH Ca (mM) Mg (mM) SO4 (mM) HS(mM) 6.0 34.27 7.7 16.3 8.0 32.30 6.9 15.5 10.0 37.55 6.6 18.8 12.0 38.82 7.7 19.5 14.0 35.35 7.2 19.5 80 16.0 36.92 8.4 18.8 0.5 2.82 11.8 0.7 2.0 2.81 10.7 4.0 3.8 6.0 2.90 10.1 11.0 3.09 11.4 0.8 16.0 2.27 10.7 72 21.0 4.03 10.6 0.3 0 2.50 7.59 0.5 2.92 7.66 11.3 0.5 2.0 2.94 7.55 11.1 4.0 2.77 7.73 10.6 0.6 6.0 2.74 7.99 10.8 11.0 3.52 8.18 12.9 38 13.0 1.4 0.5 3.03 7.70 14.4 0.4 2.0 4.60 10.9 1.8 4.0 22.93 8.34 9.2 5.4 6.0 28.68 8.1 5.0 8.0 25.28 8.47 7.5 5.7 10.0 24.77 8.45 7.4 4.8 12.0 30.07 8.47 8.5 6.6 1781 Monterey Bay – Clam Flats 28 14.0 28.93 8.6 7.5 0 2.50 – 9.9 51.6 27.9 – 0.5 3.90 7.67 9.7 49.1 27.1 0.0 1.5 4.40 7.73 9.8 48.7 26.6 0.3 2.5 5.80 8.00 9.4 48.8 25.4 0.5 3.5 6.80 7.93 9.3 48.7 24.5 1.3 4.5 8.30 8.07 9.2 49.4 23.9 1.8 5.5 11.20 8.05 9.3 51.7 22.5 3.7 8 6.5 17.30 8.05 6.8 45.4 14.5 6.9 0 2.50 – 9.8 51.6 – – 0.5 3.20 7.52 9.5 49.6 29.5 0.0 1.5 – – 9.1 49.2 28.2 0.0 2.5 4.80 8.43 8.7 50.7 27.5 0.0 5.5 – – 5.5 46.3 – – 6.5 15.40 8.23 7.1 47.2 22.2 5.4 8.5 25.30 8.14 5.8 47.2 18.5 7.6 2052 Eel River Basin 16 11.5 32.60 – 3.9 46.7 10.5 11.9

PAGE 90

79 Dive Number Location Push Core No. cm-bsf Alkalinity (mM) pH Ca (mM) Mg (mM) SO4 (mM) HS(mM) 13.5 30.80 8.21 1.4 46.4 9.3 13.1 15.5 32.10 8.21 2.1 46.1 5.2 13.5 17.5 32.40 8.29 1.3 46.1 4.1 12.7 16 19.5 33.70 8.34 0.9 51.4 3.4 13.8 0 2.50 – 9.6 50.9 27.5 – 0.5 4.60 7.78 9.6 50.4 26.3 0.5 1.5 9.60 7.90 9.0 49.0 22.1 3.7 2.5 14.00 8.12 10.8 61.5 6.0 3.5 18.30 8.10 8.4 48.6 15.1 8.4 4.5 22.10 8.24 5.9 45.7 10.4 8.5 6.5 28.00 8.22 3.2 45.2 4.5 11.3 10.5 36.10 8.22 2.0 42.5 0 16.1 12.5 35.60 8.19 1.5 45.3 0 – 14.5 36.50 8.22 0.9 45.0 0 14.7 2052 Eel River Basin 19 16.5 35.00 8.34 0.7 45.9 0 15.6 0 2.50 – 9.6 50.3 – 0.0 0.5 17.60 – 9.0 47.8 23.3 6.2 1.5 20.90 8.44 9.3 52.2 19.1 6.9 2.5 24.50 8.61 4.8 53.3 – 6.9 3.5 22.30 8.34 6.8 45.4 19.6 7.5 4.5 25.30 8.37 3.0 44.2 14.4 7.6 5.5 29.50 8.36 2.8 48.6 9.3 8.4 6.5 31.50 8.46 1.5 44.9 6.3 6.5 2 7.5 29.40 8.18 1.0 45.0 6.4 6.4 0 2.27 10.3 52.7 28.2 0.0 0.5 2.70 7.27 9.8 49.4 28.7 0.0 1.5 3.00 7.59 9.4 48.7 28.7 0.0 2.5 5.40 7.95 9.4 48.0 28.3 0.8 3.5 7.40 7.98 9.3 47.8 26.9 1.6 4.5 9.80 8.10 9.1 47.5 24.4 3.2 5.5 11.00 8.15 7.9 46.6 26.7 2.2 6.5 16.40 8.20 6.8 46.0 21.7 5.0 2054 Eel River Basin 40 7.5 17.20 8.29 5.5 54.5 23.3 4.9

PAGE 91

80 Dive Number Location Push Core Site Description Interval (cmbsf) 13CDIC 0-1 -4.60 1-3 -3.63 3-5 -4.42 5-7 -4.49 7-9 -4.48 9-11 -4.69 11-13 -4.91 11-13 -4.87 38 Reference(clam bed) 15-17 -6.09 Core top supernatant -3.72 0-1 -7.60 1-3 -15.22 3-5 -18.55 5-7 -21.07 7-9 -22.79 9-11 -22.69 31 Yellow Bacterial Mat 11-13 -22.00 0-1 -12.77 1-3 -13.33 3-5 -15.09 5-7 -15.98 7-9 -18.68 9-11 -21.00 34 White/gray Bacterial Mat 11-13 -21.16 0-1 -4.78 1-3 -4.12 3-5 -4.44 3-5 -4.40 5-7 -5.75 7-9 -6.48 9-11 -7.52 1780 Monterey BayInvertebrate Cliffs 79 Clam Bed 11-13 -8.58 Core top supernatant -3.93 0-1 -5.46 1-3 -6.85 3-5 -6.99 38 Reference(clam bed) 17-19 -21.62 0-1 -13.79 3-5 -58.15 5-7 -56.80 9-11 -49.54 11-13 -47.65 28 Bacterial Mat 13-15 -47.06 0-1 -36.47 1-3 -45.73 1781 Monterey BayClam Flats 80 Clam Bed 9-11 -41.48

PAGE 92

81 Dive Number Location Push Core Site Description Interval (cmbsf) 13CDIC 9-11 -43.95 80 Clam Bed 15-17 -42.39 1-3 -8.21 3-5 -5.81 5-7 -7.06 10-12 -11.24 15-17 -13.20 1781 Monterey BayClam Flats 72 Reference(bacterial mat) 20-22 -10.95 Core top supernatant -5.72 0-1 -13.51 2-3 -22.36 4-5 -27.09 8 Clam Bed 6-7 -33.95 Core top supernatant -5.18 0-1 -9.16 2-3 -24.06 6-7 -37.36 8-9 -38.47 13-14 -39.08 15-16 -37.85 16 Bacterial Mat 19-20 -38.81 0-1 -17.83 2-3 -31.97 4-5 -37.78 10-11 -33.49 12-13 -32.03 2052 19 Bubble Site 16-17 -30.83 Core top supernatant -6.42 0-1 -25.17 2-3 -23.86 4-5 -23.19 6-7 -19.58 2 Clam Bed 7-8 -18.15 0-1 -9.02 2-3 -18.91 4-5 -25.76 6-7 -30.57 2054 Eel River Basin 40 Bacterial Mat 7-8 -32.06

PAGE 93

82 APPENDIX B FORAMINIFERAL ISOTOPE DATA DIVE NUMBER SITE TUBECORE DEPTH (cm-bsf) SPECIES 13C 18ONO. OF INDIVIDUALS RUN LIVE/ FOSSIL Gyroidinoides altiformis -0.70 3.15 2 Uvigerina peregrina -1.36 3.09 2 Uvigerina peregrina -1.18 4.04 2 0-1 Bulimina mexicana -1.03 3.80 5 LIVE Uvigerina peregrina -1.34 4.63 0.5 Uvigerina peregrina -1.03 4.83 0.5 Uvigerina peregrina -1.35 4.62 1 Uvigerina peregrina -1.85 4.49 1 Bulimina mexicana -1.04 4.89 2 Bulimina mexicana -2.24 4.65 3 FOSSIL Uvigerina peregrina -0.89 3.11 1 Uvigerina peregrina -0.62 3.21 1 Uvigerina peregrina -0.43 3.12 1 Uvigerina peregrina -0.69 3.12 1 Globobulimina pacifica -3.87 3.42 1 1 1.5 Planulina sp. -0.22 2.63 1 LIVE Epistominella pacifica -1.09 4.61 2 Epistominella pacifica -1.11 4.65 2 FOSSIL Uvigerina peregrina -0.55 3.16 0.5 Uvigerina peregrina -0.49 3.28 1 Uvigerina peregrina -0.74 3.21 1 Uvigerina peregrina -0.22 3.25 1 Uvigerina peregrina -0.21 3.21 0.5 Uvigerina peregrina -0.57 3.15 1 Uvigerina peregrina -0.97 3.10 0.5 Gyroidinoides altiformis -0.83 3.14 2 1.52 Gyroidinoides altiformis -0.66 3.11 1 LIVE Uvigerina peregrina -1.57 4.58 1 Uvigerina peregrina -1.04 4.65 1 Uvigerina peregrina -1.31 4.58 1 Bulimina mexicana -1.19 4.72 3 FOSSIL Uvigerina peregrina -2.05 3.04 1 Uvigerina peregrina -1.13 3.17 1 Uvigerina peregrina -0.81 3.21 0.33 Uvigerina peregrina -1.14 3.07 0.33 Uvigerina peregrina -0.94 3.12 0.33 1781 CLAM FLAT 31 2 2.5 Uvigerina peregrina -0.10 3.43 0.5 LIVE

PAGE 94

83 DIVE NUMBER SITE TUBECORE DEPTH (cm-bsf) SPECIES 13C 18O NO. OF INDIVIDUALS RUN LIVE/ FOSSIL Epistominella smithi -0.92 3.57 3 Globobulimina pacifica -3.49 3.30 1 2-2.5 Epistominella pacifica -0.92 3.15 2 LIVE Epistominella pacifica -1.20 4.59 3 Epistominella pacifica -1.19 4.61 2 FOSSIL Uvigerina peregrina -1.82 3.18 1 Uvigerina peregrina -1.12 3.15 1 Uvigerina peregrina -0.25 3.21 1 Uvigerina peregrina -0.75 3.25 0.5 Uvigerina peregrina -1.39 3.27 0.5 Epistominella smithi -0.60 3.11 5 Gyroidinoides altiformis -0.66 3.11 2 Gyroidinoides altiformis -0.45 3.13 1 Epistominella pacifica -0.99 4.56 1 Epistominella pacifica -1.02 4.63 1 2.5 3 Epistominella pacifica -1.01 4.66 1 LIVE Planulina sp. 0.06 2.60 0.5 Planulina sp. 0.45 2.86 1.0 2 .5-3 Planulina sp. 0.07 2.60 0.5 LIVE Uvigerina peregrina -2.03 4.62 2 Uvigerina peregrina -1.40 4.73 1 Uvigerina peregrina -1.30 4.58 1 Bolivina spissa -1.80 4.55 3 Bolivina spissa -1.54 4.75 3 FOSSIL Uvigerina peregrina -1.17 3.15 1 Uvigerina peregrina -0.83 3.22 1 Uvigerina peregrina -1.82 3.09 1 Uvigerina peregrina -1.30 3.14 0.5 Uvigerina peregrina -0.72 3.16 0.5 Uvigerina peregrina -1.04 3.12 0.5 Gyroidinoides altiformis -0.85 3.06 1 3 4 Bulimina mexicana -1.06 3.30 4 LIVE Epistominella smithi -1.00 4.57 2 Epistominella smithi -1.89 4.64 3 Uvigerina peregrina -1.40 4.64 1 Uvigerina peregrina -1.21 4.78 1 Uvigerina peregrina -1.04 4.82 1 Uvigerina peregrina -1.36 4.58 1 Uvigerina peregrina -1.92 4.59 3 Bulimina mexicana -1.18 4.71 3 Bulimina mexicana -1.51 4.71 2 Gyroidinoides altiformis -0.67 3.18 2 FOSSIL Epistominella smithi -0.63 3.22 4 Gyroidinoides neosoldani -0.67 3.12 2 Gyroidinoides neosoldani -0.57 3.28 1 1781 CLAM FLAT 31 4-5 Gyroidinoides neosoldani -0.49 3.40 1 LIVE

PAGE 95

84 DIVE NUMBER SITE TUBECORE DEPTH (cm-bsf) SPECIES 13C 18O NO. OF INDIVIDUALS RUN LIVE/ FOSSIL Globobulimina barbata -5.36 4.52 2 Globobulimina barbata -2.77 4.47 2 Globobulimina pacifica -4.56 3.20 2 Uvigerina peregrina -0.95 3.14 2 Uvigerina peregrina -1.53 3.14 2 Uvigerina peregrina -0.78 3.07 2 Uvigerina peregrina -0.78 3.28 1 Uvigerina peregrina -1.05 3.23 1 Uvigerina peregrina -0.86 3.23 1 Uvigerina peregrina -0.51 3.13 1 Bulimina mexicana -1.17 3.22 6 1781 Clam Flats 31 4-5 Buliminella tenuata -2.76 4.40 3 LIVE Uvigerina peregrina -0.85 2.83 1 Uvigerina peregrina -0.54 3.01 1 Uvigerina peregrina -0.32 3.19 1 Uvigerina peregrina -0.71 3.06 1 Globobulimina pacifica -0.92 3.28 1 Globobulimina pacifica -1.36 3.28 1 Globobulimina pacifica -0.74 3.30 1 Globobulimina pacifica -1.46 3.28 1 Epistominella pacifica -0.79 3.09 4 Epistominella pacifica -0.73 3.10 3 0 1 Bulimina mexicana -0.82 3.26 3 LIVE Uvigerina peregrina -0.43 3.01 1 Uvigerina peregrina -0.76 3.16 1 Uvigerina peregrina -0.57 3.25 1 Globobulimina pacifica -1.29 3.45 1 Globobulimina pacifica -1.84 3.33 2 Globobulimina pacifica -1.43 3.25 1 Globobulimina pacifica -0.91 3.49 1 Epistominella pacifica -0.78 3.30 3 Epistominella pacifica -0.53 3.11 4 1 1.5 Bulimina mexicana -0.70 3.26 2 LIVE Uvigerina peregrina -0.56 3.09 1 Uvigerina peregrina -0.51 3.03 1 Uvigerina peregrina -0.49 3.07 1 Epistominella pacifica -0.50 3.22 3 Epistominella pacifica -0.72 3.23 4 Globobulimina pacifica -2.14 3.39 2 Globobulimina pacifica -2.17 3.35 2 1.5 2 Bulimina mexicana -0.72 3.29 2 LIVE Uvigerina peregrina -0.47 3.20 1 Uvigerina peregrina -0.50 3.01 1 Epistominella pacifica -0.73 3.14 3 Epistominella pacifica -0.63 3.17 2 Epistominella pacifica -0.59 3.15 2 1780 INVERTEBRATE CLIFF CLAM BED CLAM RING #1 30 2 2.5 Globobulimina pacifica -1.98 3.33 2 LIVE

PAGE 96

85 DIVE NUMBER SITE TUBECORE DEPTH (cm-bsf) SPECIES 13C 18O NO. OF INDIVIDUALS RUN LIVE/ FOSSIL Globobulimina pacifica -1.15 3.38 1 Globobulimina pacifica -0.92 3.34 1 Globobulimina pacifica -0.41 3.38 1 Bulimina mexicana -0.80 3.30 3 2-2.5 Planulina sp. 0.04 2.80 1 LIVE Uvigerina peregrina -0.57 3.23 1 Uvigerina peregrina -0.77 3.23 1 Uvigerina peregrina -0.27 3.11 1 Epistominella pacifica -0.53 3.15 2 Epistominella pacifica -0.63 3.29 2 Epistominella pacifica -0.60 3.21 2 Globobulimina pacifica -1.20 3.33 1 Globobulimina pacifica -1.68 3.41 1 Globobulimina pacifica -2.23 3.27 2 Bulimina mexicana -0.70 3.29 3 Planulina sp. 0.09 2.95 1 2.5 3 Globobulimina affinis -0.90 3.29 1 LIVE Epistominella smithi -0.59 3.15 2 Epistominella smithi -0.76 3.19 4 Bulimina mexicana -0.85 3.28 4 Globobulimina pacifica -1.06 3.28 1 Globobulimina pacifica -0.91 3.29 2 Globobulimina pacifica -1.72 3.25 3 Globobulimina pacifica -1.22 3.27 2 Uvigerina peregrina -0.33 2.97 1 Uvigerina peregrina -0.78 2.87 1 Uvigerina peregrina -0.36 3.26 1 3-4 Uvigerina peregrina -0.59 2.98 1 LIVE Epistominella smithi -0.40 3.18 1 Epistominella smithi -0.45 3.30 1 Epistominella smithi -0.35 3.18 1 Uvigerina peregrina -0.65 3.06 2 Uvigerina peregrina -0.95 3.20 2 4-5 Bulimina mexicana -0.83 3.33 3 FOSSIL Epistominella smithi -0.58 3.06 3 Epistominella smithi -0.43 3.16 2 Epistominella smithi -0.70 3.20 3 Epistominella smithi -0.48 3.16 2 Epistominella smithi -0.76 3.07 4 Epistominella smithi -0.77 3.06 6 Bulimina mexicana -0.92 3.36 3 Bulimina mexicana -0.81 3.20 4 Bulimina mexicana -0.89 3.28 3 Globobulimina pacifica -0.93 3.30 2 Globobulimina pacifica -1.81 3.23 1 Globobulimina pacifica -1.34 3.26 2 1780 INVERTEBRATE CLIFF CLAM BED CLAM RING #1 30 4-5 Globobulimina pacifica -1.47 3.33 3 LIVE

PAGE 97

86 DIVE NUMBER SITE TUBECORE DEPTH (cm-bsf) SPECIES 13C 18O NO. OF INDIVIDUALS RUN LIVE/ FOSSIL Uvigerina peregrina -0.59 2.59 1 Uvigerina peregrina -0.04 3.11 1 Uvigerina peregrina -0.45 2.91 1 Uvigerina peregrina -0.43 3.14 1 Uvigerina peregrina -0.36 3.40 1 Uvigerina peregrina -0.37 3.15 1 Uvigerina peregrina -0.36 3.10 1 INVERTEBRATE CLIFFS CLAM BED CLAM RING #1 30 4-5 Uvigerina peregrina -0.49 2.66 1 LIVE Epistominella smithi -0.72 3.31 4 0-1 Globobulimina pacifica -1.22 3.34 3 LIVE Epistominella smithi -0.66 3.19 3 FOSSIL 1-1.5 Uvigerina peregrina -0.61 3.13 3 Uvigerina peregrina -0.80 3.16 1 Globobulimina pacifica -1.12 3.19 2 1.5-2 Globobulimina pacifica -1.50 3.25 2 Epistominella pacifica -0.59 3.21 4 2 2.5 Uvigerina peregrina -1.04 3.14 1 1780 INVERTEBRATE CLIFF GRAY BACTERIAL MAT CLAM RING # 1 67 2.5 3 Epistominella pacifica -0.62 3.19 2 LIVE Dive No. Site Hydraulic Push Core No. Depth (cm-bsf) Species (all are fossil (?)) 13C 18O No. of individuals run Planulina sp. 0.13 2.55 1 Bulimina mexicana -0.72 3.26 3 Uvigerina peregrina -0.70 3.26 1 Uvigerina peregrina -0.95 3.17 4 Epistominella pacifica -0.50 3.22 1 Epistominella pacifica -0.41 3.47 1 0.5 Epistominella pacifica -0.47 3.48 1 Uvigerina peregrina -0.30 3.06 0.5 Uvigerina peregrina 0.01 3.22 0.5 Uvigerina peregrina -0.12 3.27 0.5 Epistominella pacifica -0.64 3.34 2 1.5 Epistominella pacifica -0.52 3.24 2 2.5 Epistominella pacifica -0.42 3.35 1 Epistominella pacifica -0.33 3.23 1 Epistominella pacifica -0.52 3.20 1 Bulimina mexicana -1.04 3.28 2 Bulimina mexicana -1.00 3.05 2 Globobulimina pacifica -0.73 3.33 3 1780 Monterey Bay Invertebrate Cliffs Clam bed 5 4 Globobulimina pacifica -0.78 3.38 3

PAGE 98

87 Dive No. Site Hydraulic Push Core No. Depth (cm-bsf) Species (all are fossil (?)) 13C 18O No. of individuals run Buliminella tenuata -1.59 2.98 1 4 Uvigerina peregrina -0.35 3.33 1 Uvigerina peregrina -0.60 3.36 1 Buliminella tenuata -1.85 3.03 2 Bulimina mexicana -0.91 3.72 2 5.5 Epistominella pacifica -0.52 3.26 2 7.5 Epistominella pacifica -1.06 3.03 3 8.5 Epistominella pacifica -0.78 3.51 1 9.5 Epistominella pacifica -0.43 3.24 1 Epistominella pacifica -0.50 3.20 1 Epistominella pacifica -0.27 3.19 1 Uvigerina peregrina -0.22 3.12 0.5 Globobulimina pacifica -1.37 3.36 2 10.5 Uvigerina peregrina -0.25 3.25 1 Globobulimina pacifica -1.04 3.31 1 Globobulimina pacifica -1.03 3.40 1 Epistominella pacifica -0.41 3.28 1 Epistominella pacifica -0.27 3.27 1 Uvigerina peregrina -0.75 3.24 1 Uvigerina peregrina -0.83 3.34 2 Uvigerina peregrina -0.44 3.09 0.5 11.5 Uvigerina peregrina -0.66 3.22 0.5 Uvigerina peregrina -1.00 3.15 3 Epistominella pacifica -0.47 3.19 1 12.5 Epistominella pacifica -0.39 3.22 1 Globobulimina pacifica -1.17 3.61 2 Uvigerina peregrina -0.28 3.48 1 Uvigerina peregrina -0.51 3.24 1 Bulimina mexicana -0.84 3.68 3 Epistominella pacifica -0.40 3.19 1 13.5 Epistominella pacifica -0.43 3.34 1 Uvigerina peregrina -0.94 3.23 2 Uvigerina peregrina -0.50 3.36 1 Uvigerina peregrina -0.62 3.22 0.5 Uvigerina peregrina -0.51 3.12 0.5 Bulimina mexicana -0.73 3.51 2 Bulimina mexicana -0.71 3.49 2 Epistominella pacifica -0.36 3.21 1 Epistominella pacifica -0.13 3.54 1 Epistominella pacifica -0.47 3.16 2 Globobulimina pacifica -1.08 3.37 2 14.5 Globobulimina pacifica -1.11 3.40 2 Globobulimina pacifica -1.03 3.26 1 1780 Monterey Bay Invertebrate Cliffs Clam bed 5 15.5 Uvigerina peregrina -0.25 3.20 1

PAGE 99

88 Dive No. Site Hydraulic Push Core No. Depth (cm-bsf) Species (all are fossil (?)) 13C 18O No. of individuals run Uvigerina peregrina -0.08 3.10 0.5 Epistominella pacifica -0.33 3.35 1 Epistominella pacifica -0.51 3.46 1 15.5 Buliminella tenuata -1.36 3.54 1 Buliminella tenuata -1.09 3.50 2 Uvigerina peregrina -0.91 3.22 1 Epistominella pacifica -0.39 3.29 1 Epistominella pacifica -0.31 3.40 1 Epistominella pacifica -0.46 3.43 1 Epistominella pacifica -0.47 3.29 1 Epistominella pacifica -0.45 3.32 1 Epistominella pacifica -0.54 3.07 1 Epistominella pacifica -0.44 3.46 1 Epistominella pacifica -0.39 3.36 1 Epistominella pacifica -0.57 3.13 2 16.5 Epistominella pacifica -0.34 3.37 1 Epistominella pacifica -0.50 2.31 1 17.5 Epistominella pacifica -0.31 3.60 1 Epistominella pacifica -0.50 3.23 1 Epistominella pacifica -0.39 3.40 1 18.5 Epistominella pacifica -0.39 3.34 1 Epistominella pacifica -0.39 3.25 1 Epistominella pacifica -0.42 3.34 1 19.5 Bulimina mexicana -0.56 3.52 1 Uvigerina peregrina -0.72 3.40 1 Uvigerina peregrina -0.87 3.32 3 Epistominella pacifica -0.26 3.27 1 Epistominella pacifica -0.40 3.53 1 20.5 Buliminella tenuata -1.05 3.29 2 Buliminella tenuata -1.45 3.39 2 Buliminella tenuata -0.81 3.41 1 Buliminella tenuata -0.93 3.43 1 Buliminella tenuata -1.54 3.25 4 Planulina sp. 0.22 2.70 0.5 Planulina sp. 0.26 2.50 0.5 Epistominella pacifica -0.41 3.29 1 Epistominella pacifica -0.23 3.36 1 Uvigerina peregrina -0.82 3.36 1 Uvigerina peregrina -0.77 3.08 1 Bulimina mexicana -0.97 3.28 3 Bulimina mexicana -0.69 3.14 3 Globobulimina pacifica -1.35 3.37 1 Globobulimina pacifica -1.07 3.30 2 1780 Monterey Bay Inverteb rate Cliffs Clam bed 5 21.5 Globobulimina pacifica -0.90 3.40 1

PAGE 100

89 Dive No. Site Hydraulic Push Core No. Depth (cm-bsf) Species (all are fossil (?)) 13C 18O No. of individuals run Globobulimina pacifica -0.81 3.49 3 Globobulimina pacifica -1.08 3.37 1 21.5 Globobulimina pacifica -0.97 3.40 1 Uvigerina peregrina -0.55 3.15 1 Uvigerina peregrina -0.71 3.25 1 Bulimina mexicana -0.87 3.49 2 Bulimina mexicana -0.56 3.42 2 Globobulimina pacifica -0.61 3.38 1 Globobulimina pacifica -1.07 3.33 1 Buliminella tenuata -1.82 3.64 1 22.5 Epistominella pacifica -0.34 3.31 1 Bulimina mexicana -0.57 3.64 1 Bulimina mexicana -0.69 3.39 3 Epistominella pacifica -0.44 3.22 1 Epistominella pacifica -0.21 3.16 1 Buliminella tenuata -1.35 3.18 3 Buliminella tenuata -1.43 3.17 2 Globobulimina pacifica -1.69 3.42 1 Globobulimina pacifica -1.04 3.29 2 23.5 Uvigerina peregrina -0.97 3.25 5 Epistominella pacifica -0.49 3.24 1 Epistominella pacifica -0.51 3.25 2 24.5 Bulimina mexicana -0.71 3.37 2 Bulimina mexicana -0.52 3.89 2 Uvigerina peregrina -0.60 3.73 1 Uvigerina peregrina -1.05 3.12 1 Epistominella pacifica -0.50 3.28 2 25.5 Epistominella pacifica -0.50 3.34 2 Buliminella tenuata -1.27 3.29 2 Uvigerina peregrina -0.72 3.28 2 Epistominella pacifica -0.32 3.15 1 Epistominella pacifica -0.29 3.15 1 Globobulimina pacifica -1.09 3.35 1 26.5 Globobulimina pacifica -1.19 3.42 1 Epistominella pacifica -0.32 3.30 1 27.5 Epistominella pacifica -0.60 3.22 4 28.5 Epistominella pacifica -0.38 3.47 1 Epistominella pacifica -0.34 3.30 1 Epistominella pacifica -0.29 3.18 1 Epistominella pacifica -0.31 3.27 1 Epistominella pacifica -0.56 3.23 1 Epistominella pacifica -0.38 3.26 1 Epistominella pacifica -0.22 3.28 1 1780 Monterey Bay Inverteb rate Cliffs Clam bed 5 29.5 Epistominella pacifica -0.40 3.02 1

PAGE 101

90 Dive No. Site Hydraulic Push Core No. Depth (cm-bsf) Species (all are fossil (?)) 13C 18O No. of individuals run Epistominella pacifica -0.62 3.20 2 Epistominella pacifica -0.54 3.23 2 Bulimina mexicana -0.66 3.94 2 Globobulimina pacifica -0.87 3.30 1 Globobulimina pacifica -0.83 3.68 2 29.5 Globobulimina pacifica -1.02 3.71 3 Epistominella pacifica -0.39 3.45 1 Epistominella pacifica -0.68 3.26 2 Monterey Bay Invertebrate Cliffs Clam bed 5 31.5 Epistominella pacifica -0.80 3.28 3 Globobulimina pacifica -1.37 3.52 1 Epistominella pacifica -0.37 3.24 1 29.5 Epistominella pacifica -0.57 3.19 1 Epistominella pacifica -0.46 3.26 1 Epistominella pacifica -0.35 3.28 1 Epistominella pacifica -0.51 3.39 1 Epistominella pacifica -0.75 3.26 2 Epistominella pacifica -0.66 3.34 1 Epistominella pacifica -0.54 3.19 2 30.5 Bulimina mexicana -0.90 3.41 4 Globobulimina pacifica -2.01 3.57 2 Epistominella pacifica -0.29 3.33 1 31.5 Epistominella pacifica -0.45 3.48 3 Globobulimina pacifica -1.53 3.46 1 36.5 Bulimina mexicana -0.71 3.26 1 38.5 Epistominella pacifica -0.59 3.09 3 Epistominella pacifica -0.45 3.41 1 Epistominella pacifica -0.38 3.37 1 Epistominella pacifica -0.49 3.29 2 Epistominella pacifica -0.56 3.24 2 Epistominella pacifica -0.59 3.41 2 39.5 Buliminella tenuata -1.62 3.16 1 Uvigerina peregrina -0.85 3.36 1 Epistominella pacifica -0.62 3.38 2 1780 Monterey Bay Invertebrate Cliffs (between yellow and white bacterial mats) 2 41.5 Globobulimina pacifica -2.19 3.33 1

PAGE 102

91 DIVE NUMBER SITE LONG CORE Depth (cm) SPECIES (all are fossil (?))13C 18O NO. OF INDIVIDUALS RUN Uvigerina peregrina -17.01 4.44 1 Uvigerina peregrina -1.16 2.99 2 0.5 Uvigerina peregrina -0.81 2.94 1 1.5 Uvigerina peregrina -8.90 3.52 2 Uvigerina peregrina -0.74 2.93 1 3.5 Uvigerina peregrina -0.96 3.01 1 Uvigerina peregrina -8.03 4.02 1 4.5 Epistominella pacifica -0.49 3.14 2 Uvigerina peregrina -0.65 3.04 1 Uvigerina peregrina -0.79 2.92 1 Uvigerina peregrina -0.86 2.99 1 Uvigerina peregrina -1.23 3.90 1 Uvigerina peregrina -1.16 2.93 1 Epistominella pacifica -1.87 4.03 2 5.5 Bulimina mexicana -18.09 4.22 2 Bulimina mexicana -18.68 4.06 3 Epistominella pacifica -0.66 2.76 1 Uvigerina peregrina -15.31 3.84 1 6.5 Uvigerina peregrina -1.03 3.09 1 Uvigerina peregrina -3.07 3.94 1 Uvigerina peregrina -14.08 4.76 1 Epistominella pacifica -0.75 3.42 2 7.5 Bulimina mexicana -11.85 3.96 3 Bulimina mexicana -19.67 4.21 4 Epistominella pacifica -15.24 3.72 5 8.5 Uvigerina peregrina -11.56 3.96 1 Uvigerina peregrina -23.22 4.46 1 Uvigerina peregrina -5.37 3.72 1 Bulimina mexicana -21.13 4.26 2 9.5 Epistominella pacifica -0.90 2.94 3 Bulimina mexicana -20.48 4.51 1 Epistominella pacifica -0.78 2.85 1 Epistominella pacifica -0.85 2.85 1 Epistominella pacifica -0.98 2.88 1 Epistominella pacifica -0.50 3.04 1 Epistominella pacifica -0.81 2.99 1 Uvigerina peregrina -1.05 2.78 1 Uvigerina peregrina -1.80 2.14 1 Uvigerina peregrina -13.83 4.00 1 Uvigerina peregrina -1.24 2.91 1 Uvigerina peregrina -16.63 3.63 1 2052 Bubble Site Long Core 2 10.5 Uvigerina peregrina -21.93 4.27 1

PAGE 103

92 DIVE NUMBER SITE LONG CORE Depth (cm) SPECIES (all are fossil (?))13C 18O NO. OF INDIVIDUALS RUN Uvigerina peregrina -0.72 3.86 1 Epistominella pacifica -0.48 2.95 1 11.5 Bulimina mexicana -8.61 3.89 3 Bulimina mexicana -15.81 4.19 2 Epistominella pacifica -14.14 3.83 4 12.5 Uvigerina peregrina -11.75 3.98 1 Uvigerina peregrina -8.69 3.99 1 Bulimina mexicana -10.98 3.87 4 13.5 Bulimina mexicana -12.62 4.04 3 Bulimina mexicana -10.78 3.97 2 Uvigerina peregrina -10.81 4.02 1 14.5 Epistominella pacifica -5.92 3.85 4 Epistominella pacifica -5.37 3.91 3 Uvigerina peregrina -1.50 3.78 2 15.5 Bulimina mexicana -7.81 3.85 3 Uvigerina peregrina -13.18 4.05 1 16.5 Epistominella pacifica -11.54 3.93 4 Epistominella pacifica -0.78 3.51 6 Uvigerina peregrina -0.99 4.09 1 17.5 Bulimina mexicana -0.71 4.07 1 Bulimina mexicana -9.12 3.88 2 Bulimina mexicana -4.59 3.83 3 Uvigerina peregrina -1.18 3.88 2 Bubble Site Long Core 2 18.5 Epistominella pacifica -0.16 3.83 1 Uvigerina peregrina -1.05 3.11 1 0.5 Epistominella pacifica -0.89 3.72 1 Epistominella pacifica -19.46 4.27 1 Uvigerina peregrina -1.19 2.81 1 Uvigerina peregrina -0.65 3.35 1 Uvigerina peregrina -0.62 3.12 1 Uvigerina peregrina -6.87 3.70 1 1.5 Uvigerina peregrina -1.09 3.01 2 2.5 Uvigerina peregrina -0.95 3.02 1 Uvigerina peregrina -0.81 2.85 1 Uvigerina peregrina -0.86 3.62 1 Epistominella pacifica -2.67 3.60 3 3.5 Epistominella pacifica -0.65 3.22 4 Epistominella pacifica -0.96 3.08 2 4.5 Uvigerina peregrina -2.90 3.84 1 5.5 Uvigerina peregrina -7.13 4.05 1 Uvigerina peregrina -1.11 2.86 1 2052 Clam Bed Long Core 4 9.5 Uvigerina peregrina -1.00 3.64 1

PAGE 104

93 DIVE NUMBER SITE LONG CORE Depth (cm) SPECIES (all are fossil (?))13C 18O NO. OF INDIVIDUALS RUN Epistominella pacifica -7.96 4.00 1 Epistominella pacifica -2.67 3.69 3 9.5 Epistominella pacifica -3.44 3.69 3 Epistominella pacifica -1.39 3.90 1 Epistominella pacifica -1.22 3.73 2 Epistominella pacifica -1.34 3.69 3 Epistominella pacifica -1.10 3.67 3 10.5 Uvigerina peregrina -0.78 3.76 1 Uvigerina peregrina -0.73 3.72 1 Uvigerina peregrina -1.34 3.65 1 Uvigerina peregrina -0.80 3.75 1 Uvigerina peregrina -0.46 3.89 0.5 Uvigerina peregrina -1.11 3.70 0.5 Uvigerina peregrina -1.20 3.66 1 Uvigerina peregrina -1.29 3.64 1 11.5 Epistominella pacifica -0.79 3.68 2 Epistominella pacifica -0.75 3.62 2 Epistominella pacifica -0.81 3.58 3 Uvigerina peregrina -0.78 3.58 0.5 12.5 Uvigerina peregrina -0.51 3.78 0.5 Uvigerina peregrina -0.97 3.62 1 Uvigerina peregrina -0.85 3.73 1 13.5 Epistominella pacifica -1.03 3.48 4 Epistominella pacifica -0.74 3.71 2 Uvigerina peregrina -0.62 4.00 1 14.5 Uvigerina peregrina -0.52 3.71 1 Uvigerina peregrina -0.87 3.80 1 Uvigerina peregrina -0.61 3.82 1 15.5 Epistominella pacifica -0.83 3.59 3 Epistominella pacifica -1.27 3.69 3 16.5 Uvigerina peregrina -2.04 3.67 2 17.5 Epistominella pacifica -8.86 4.30 1 Uvigerina peregrina -1.38 3.61 1 Clam Bed Long Core 4 18.5 Uvigerina peregrina -0.74 3.70 1 0.5 Uvigerina peregrina -0.95 3.57 3 Uvigerina peregrina -1.16 2.99 1 Uvigerina peregrina -6.97 3.70 2 1.5 Epistominella pacifica -0.32 3.46 3 Epistominella pacifica -0.55 3.37 3 Uvigerina peregrina -0.65 3.85 1 2.5 Uvigerina peregrina -1.03 3.61 1 3.5 Uvigerina peregrina -1.18 3.93 1 2052 Bacterial Mat Long Core 5 9.5 Uvigerina peregrina -1.22 3.66 2

PAGE 105

94 DIVE NUMBER SITE LONG CORE Depth (cm) SPECIES (all are fossil (?))13C 18O NO. OF INDIVIDUALS RUN 9.5 Epistominella pacifica -0.48 3.82 1 11.5 Epistominella pacifica -1.01 3.60 4 12.5 Uvigerina peregrina -1.13 3.60 1 13.5 Uvigerina peregrina -0.58 3.77 2 Uvigerina peregrina -0.49 3.71 1 14.5 Epistominella pacifica -0.74 3.72 3 Epistominella pacifica -0.94 3.66 4 Uvigerina peregrina -0.65 3.78 1 Uvigerina peregrina -0.73 3.70 1 15.5 Uvigerina peregrina -0.86 3.64 1 16.5 Uvigerina peregrina -1.08 3.58 2 Uvigerina peregrina -1.12 3.67 2 17.5 Epistominella pacifica -0.87 3.70 3 Epistominella pacifica -0.77 3.73 3 Epistominella pacifica -0.88 3.67 3 Uvigerina peregrina -0.67 3.83 1 18.5 Uvigerina peregrina -1.24 3.62 3 Uvigerina peregrina -1.12 3.66 2 Uvigerina peregrina -1.29 3.60 3 19.5 Epistominella pacifica -0.85 3.57 5 Epistominella pacifica -0.83 3.69 3 Epistominella pacifica -0.99 3.97 4 Uvigerina peregrina -0.88 3.72 1 Uvigerina peregrina -0.78 3.81 1 20.5 Uvigerina peregrina -0.91 3.73 1 Uvigerina peregrina -1.00 3.60 4 21.5 Epistominella pacifica -0.92 3.57 4 Epistominella pacifica -0.85 3.61 4 Uvigerina peregrina -0.73 3.71 1 Uvigerina peregrina -0.71 3.96 1 22.5 Uvigerina peregrina -0.41 3.79 0.5 Uvigerina peregrina -1.77 3.84 1 Uvigerina peregrina -0.82 3.69 1 23.5 Epistominella pacifica -0.65 3.70 2 Uvigerina peregrina -0.90 3.66 1 Uvigerina peregrina -1.24 3.53 4 24.5 Uvigerina peregrina -1.21 3.71 4 Uvigerina peregrina -0.93 3.65 1 Uvigerina peregrina -0.68 3.97 1 25.5 Epistominella pacifica -0.57 3.75 3 Epistominella pacifica -0.50 3.73 2 Uvigerina peregrina -4.48 3.79 0.5 26.5 Uvigerina peregrina -0.67 3.72 1 2052 Bacterial Mat Long Core 5 27.5 Uvigerina peregrina -11.59 3.91 1

PAGE 106

95 APPENDIX C SEM PHOTOMICROGRAPHS For all of the following, the picture on the left will show an overall view of the foraminifera, whereas the picture on the right will be a close-up of an identified region. (a). Broken live Uvigerina peregrina (top portion near aperture) from Dive 1780 PC30 (Invertebrate Cliffs (IC) clam bed) 0-1 cm. (b). A live Epistominella smithi from Dive 1780 PC67 0-1cm (IC gray bacterial mat). (c). A fossil (?) U. peregrina from Dive 1780 HPC5 15-16 cm (IC clam bed).

PAGE 107

96 (d). A fossil (?) U. peregrina from Dive 1780 HPC5 21-22 cm (IC clam bed). (e). A fossil (?) U. peregrina from Dive 1780 HPC5 29-30 cm (IC clam bed). (f). A fossil (?) E. pacifica from Dive 1780 HPC5 0-1 cm (IC clam bed). (g). A fossil (?) E. pacifica from Dive 1780 HPC5 16-17 cm (IC clam bed). The micrograph shows the dorsal view.

PAGE 108

97 (h). A dorsal view of a fossil (?) E. pacifica photographed prior to cleaning from Dive 1780 HPC5 27-28 cm (IC clam bed). (i). A fossil (?) E. pacifica from 2052 LC2 10-11 cm (Eel River Basin (ERB) bubble site). (j). A fossil (?) E. pacifica from 2052 LC4 1-2 cm (ERB clam bed). Specimen was not cleaned before photographing.

PAGE 109

98 (k). A fossil (?) E. pacifica from Dive 2052 LC4 11-12 cm (ERB clam bed) photographed prior to cleaning. (l). A view inside th e test of a fossil (?) U. peregrina from Dive 2052 LC4 12-13 cm (ERB clam bed). (m). A fossil (?) U. peregrina from Dive 2052 LC4 17-18 cm (ERB clam bed).

PAGE 110

99 (n). A fossil (?) E. pacifica (?) from Dive 2052 LC4 18-19 cm (ERB clam bed). (o). A fossil (?) E. pacifica from Dive 2052 LC5 0-1 cm (ERB bacterial mat). (p). A fossil (?) U. peregrina from Dive 2052 LC5 1-2 cm (ERB bacterial mat). (q). A fossil (?) E. pacifica from Dive 2052 LC5 12-13 cm (ERB bacterial mat).

PAGE 111

100 (r). A fossil (?) U. peregrina from Dive 2052 LC5 15-16 cm (E RB bacterial mat). A hair and possibly a fragment of a diatom we re transferred to the foram during SEM preparation. (s). A broken fossil (?) U. peregrina from Dive 2052 LC5 25-26 cm (ERB bacterial mat). (t). A fossil (?) E. pacifica from Dive 2052 LC1 4-5 cm (ERB reference core) photographed prior to cleaning.

PAGE 112

101 (u). A broken fossil (?) U. peregrina from Dive 1781 HPC5 0-1 cm (Clam Flats clam bed). Photographed before cleaning.

PAGE 113

102 LIST OF REFERENCES Aharon, P., E.R. Graber, and H.H. Roberts, 1992. Dissolved carbon and 13C anomalies in the water column caused by hydrocar bon seeps on the north western Gulf of Mexico slope. Geo-Ma rine Letters, 12: 33-40. Aharon, P. M. Hackworth, E. Platon, C. Wheeler, and B. Sen Gupta, 2001. Isotope records of recent benthic foraminifera from hydrate-bearing sediments: methanehydrate dissociation effects. GSA Abstracts with Programs, 33: A162. Barry, J.P., H.G. Greene, D.L. Orange, C.H. Baxter, B.H. Robison, R.E. Kochevar, J.W. Nybakken, D.L. Reed, and C.M. McHugh, 1996. Biologic and geologic characteristics of cold seeps in Monter ey Bay, California. Deep-Sea Research, 43 (11-12): 1739-1762. Barry, J.P., R.E. Kochevar, and C.H. Ba xter, 1997. The influence of pore-water chemistry and physiology on the distribution of vesicomyid clams at cold seeps in Monterey Bay: Implications for patterns of chemosynthetic community organization. Limnology a nd Oceanography, 42 (2): 318-328. Berner, R.A., 1980. Early Diagenesis: A Theoretical Approach Princeton University Press, Princeton, New Jersey. Bernhard, J.M., 1988. Postmortem vital stai ning in benthic forami nifera: duration and importance in population and distributional studies. Journal of Foraminiferal Research, 18 (2): 143-146. Bernhard, J.M., K.R. Buck, and J.P. Barr y, 2001. Monterey Bay cold-seep biota: Assemblages, abundance, and ultrastructu re of living foraminifera. Deep-Sea Research I, 48: 2233-2249. Blair, N.E., and R.C. Aller, 1995. Anaerobi c methane oxidation on the Amazon shelf. Geochimica et Cosmochimica Acta, 59 (18): 3707-3715. Blunier, Thomas. 2000. "Frozen" methane escapes from the seafloor. Science, 288: 6869. Boltovskoy, E., and R. Wright, 1976. Recent Foraminifera Dr. W. Junk Publishers, The Hague.

PAGE 114

103 Brewer, P.G., F.M. Orr, G. Friederich, K.A. Kvenvolden, D.L. Orange, J. McFarlane, and W. Kirkwood, 1997. Deep-ocean field test of methane hydrate formation from a remotely operated vehicle. Geology, 25 (5): 407-410. Brooks, J.M., M.E. Field, and M.C. Kennicutt II, 1991. Observations of gas hydrates in marine sediments, offshore northern California. Marine Geology, 96: 103-109. Burger, R.L., C.S. Fulthorpe, J.A. Austin Jr., and S. P.S. Gulick, 2002. Lower Pleistocene to present st ructural deformation and sequence stratigraphy of the continental shelf, offshore Eel River Ba sin, northern Californi a. Marine Geology, 185: 249-281. Cavagna, S., P. Clari, and L. Martire, 1999. The role of bacteria in the formation of cold seep carbonates: geological evidence fr om Monferrato (Tertiary, NW Italy). Sedimentary Geology, 126: 253-270. Corliss, B.H., 1985. Microhabitats of benthic foraminifera within deep-sea sediments. Nature, 314 (4): 435-438. Corliss, B.H. and S. Emerson, 1990. Distri bution of Rose Bengal stained deep-sea benthic foraminifera from the Nova Sc otian continental margin and Gulf of Maine. Deep-Sea Research, 37 (3): 381-400. Curry, W.B., J.C. Duplessy, L.D. Labeyrie and N.J. Shackleton, 1988. Changes in the distribution of 13C of deep water CO2 between the last glaciation and the Holocene. Paleoceanography, 3 (3): 317-341. DeLong, E.F., 2000. Resolving a meth ane mystery. Nature, 407: 577-579. Dickens, Gerald R., 2001. The potential volume of oceanic methane hydrates with variable external conditions. Organic Geochemistry, 32: 1179-1193. Dickens, G.R., J.R. O’Neil, D.K. Rea, a nd R.M. Owen, 1995. Dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the Paleocene. Paleoceanography, 10: 965-971. Furlong, K.P. and R. Govers, 1999. Ephemeral cr ustal thickening at a triple junction: the Mendocino crustal conve yor. Geology, 27: 127-130. Gieskes, J.M., T. Gamo, and H. Brumsack, 1991. Chemical methods for interstitial water analysis on JOIDES Resolution. ODP Technical Note 15, 60 p. Goldstein, S.T., 1999. “Foraminifer a: A biological overview.” Modern Foraminifera Ed. B.K. Sen Gupta. Kluwer Academic Publishers, London, England. 37-55.

PAGE 115

104 Goldstein, S.T., and B.H. Corliss, 1994. Deposit feeding in selected deep-sea and shallow-water benthic foraminife ra. Deep-Sea Research, 41: 229-241. Greene, H.G., D.L. Orange, and J.P. Barr y, 1993. Geologic diversity of cold seep communities, Monterey Bay region, central California, USA. Transactions, American Geophysical Union, 74: 578. Greene, H.G., W.L. Stubblefield, and A.E. Theberge Jr., 1989. Geology of the Monterey submarine canyon system and adjacent areas offshore central California. USGS Open File Report, 89-221. Grossman, E.L., 1987. Stable isotopes in m odern benthic foraminifera: a study of vital effect. Journal of Foramini feral Research, 17(1): 48-61. Houghton, J.T., G.J. Jenkins and J.J Ephraums, (eds.), 1990. Climate Change: The IPCC Scientific Assessment Cambridge Univ Press, New York, New York. Jorrisen, F.J., 1999. “Benthic foraminiferal microhabitats below the sediment-water interface.” Modern Foraminifera Ed. B.K. Sen Gupta. Kluwer Academic Publishers, London, England. 37-55. Kennett, J.P., I.L. Hendy, and R. J. Behl, 1996. Late Quaternary foraminiferal carbon isotopic record in Santa Barbara Basin: Implications for rapid climate change. Eos Trans. AGU 77 (46): 294. Kennett, J.P., K.G. Cannariato, I.L. Hendy, and R.J. Behl, 2000. Carbon isotopic evidence for methane hydrate instability duri ng quaternary interstadials. Science, 288: 128-133. Kvenvolden, K., 1988. Methane hydrates and global climate change. Global Biogeochemical Cycles, 2: 221-229. Kvenvolden, K.A., and M.E. Field, 1985. Gas hydrates on the northern California continental margin. Geology, 13: 517-520. Kvenvolden, K.A, G.D. Ginsbur g, and V.A. Soloviev, 1993. Worldwide distribution of subaquatic gas hydrates. Ge o-Marine Letters, 13: 32-40. LaRock, P.A., J.-H. Hyun, and B.W. Benni son, 1994. Bacterioplankton growth and production at the Louisiana hydrocarbon s eeps. Geo-Marine Letters, 14: 104-109. Lewis, R.C., K.H. Coale, B.D. Edwards, M. Marot, J. N. Douglas, and E.J. Burton, 2002. Accumulation rate and mixi ng of shelf sediments in the Monterey Bay National Marine Sanctuary. Marine Geology, 181: 157-169.

PAGE 116

105 Lorenson, T.D., K.A. Kvenvolden, F.D. Hostet tler, R.J. Rosenbauer, D.L. Orange, and J.B. Martin, 2002. Hydrocarbon geochemistry of cold seeps in the Monterey Bay National Marine Sanctuary. Marine Geology, 181: 285-304. MacDonald, G.J., 1990. Role of methane clathrates in past and future climates. Climatic Change, 16: 247-281. Mackensen, A., and R.G. Douglas, 1989. Down-c ore distribution of live and dead deepwater benthic foraminifera in box cores from the Wedell Sea and the California continental borderland. Deep -Sea Research, 36 (6): 879-900. Martin, J.B., M. Kastner, P. Henry, X. Le Pichon, and S. Lallement, 1996. Chemical and isotopic evidence for sources of fluids in a mud volcano field seaward of the Barbados accretionary wedge. Jour nal of Geophysical Research, 101: 2032520345. Martin, J.B., D.L. Orange, T.D. Lorenson, and K.A. Kvenvolden, 1997. Chemical and isotopic evidence of gas-influenced flow at a transform plate boundary: Monterey Bay, California. Journal of Geophysical Research, 102: 24903-24915. McConnaughey, T., 1989. 13C and 18O isotopic disequilibrium in biological carbonates: I patterns. Geochimica et Cosmochimica acta, 53: 151-162. McCorkle, D.C., L.D. Keigwin, B.H. Corliss, and S.R. Emerson, 1990. The influence of microhabitats on the carbon isotopi c composition of deep-sea benthic foraminifera. Paleoceanography, 5: 161-185. McCorkle, D.C., B.H. Corliss, and C.A. Farnham, 1997. Verti cal distributions and stable isotopic compositions of liv e (stained) benthic foraminifera from the North Carolina and California contin ental margins. Deep S ea Research I, 44 (6): 9831024. Nisbet, E. 1990. Climate change and methane. Nature, 347: 23. Orange, D.L., H.G. Greene, D. Reed, J.B. Martin, C.M. McHugh, W.B.F. Ryan, N. Maher, D. Stakes, and J.P. Barry, 1999. Widespread fluid expulsion on a translational continental margin: Mud vol canoes, fault zones, headless canyons, and organic-rich substrate in Monterey Bay, California. GSA Bulletin, 111 (7): 992-1009. Parkhurst, D.L. and Appelo, C.A.J., 1999, Us er's guide to PHREEQC (Version 2)—A computer program for speciation, batch -reaction, one-dimensional transport, and inverse geochemical calculations: U.S. Geological Survey Water-Resources Investigations Report 99-4259, 310 p.

PAGE 117

106 Page, B.M., 1970. Sur-Nacimiento fault z one of California: Continental margin tectonics. GSA Bulletin, 81: 667-690. Rathburn A.E., and B.H. Corliss, 1994. The ecology of living (stain ed) deep-sea benthic foraminifera from the Sulu Sea. Paleoceanography, 9 (1): 87-150. Rathburn, A.E., B.H. Corliss, K.D. Tappa, and K.C. Lohmann, 1996. Comparisons of the ecology and stable isotopic compositions of living (stained) deep-sea benthic foraminifera from the Sulu and South Ch ina Seas. Deep-Sea Research 43 (10): 1617-1646. Rathburn, A.E., L. Levin, Z. Held, and K. C. Lohmann, 2000. Benthic foraminifera associated with cold methane seeps on the northern California margin: Ecology and stable isotopic composition. Ma rine Micropaleontology, 38: 247-266. Reeburgh, W.S., 1976. Methane consumption in Cariaco Trench waters and sediments. Earth and Planetary Scie nce Letters, 28: 337-344. Reimers, C.E., K.C. Ruttenberg, D.E. Cannf ield, M.B. Christiansen, and J.B. Martin, 1996. Pore water pH and authigenic phases formed in the uppermost sediments of the Santa Barbara Basin. Geochimica et Cosmochimica Acta, 60 (21): 40374057. Seigle, G.A., 1973. Pyritization in living fo raminifers. Journal of Foraminiferal Research, 3(1): 1-6. Sen Gupta, B.K., and P. Aharon, 1994. Bent hic foraminifera of bathyal hydrocarbon vents of the Gulf of Mexico: Initial Re port on communities and stable isotopes. Geo-marine Letters, 14: 88-96. Sen Gupta, B.K., E. Platon, J.M. Bernhard, and P. Aharon, 1997. Foraminiferal colonization of hydrocarbon-seep bacterial mats and underlying sediment, Gulf of Mexico slope. Journal of Fora miniferal Research, 27 (4): 292-300. Severinghaus, J.P., T. Sowers, E.J. Brook, R.B. Alley, and M.L. Bender, 1998. Timing of abrupt climate change at the end of the Younger-Dryas interval from thermally fractionated gases in polar ic e. Nature, 391 (6663): 141-146. Sommerfield, C.K., and C.A. Nittrouer, 1999. Modern accumulation rates and a sediment budget for the Eel Shelf: A fl ood-dominated depositional environment. Marine Geology, 154: 227-241. Stakes, D.S., D.L. Orange, J.B. Paduan, K.A. Salamy, and N. Maher, 1999. Cold-seeps and authigenic carbonate formation in Monterey Bay, California. Marine Geology, 159: 93-109.

PAGE 118

107 Stott, L.D. W. Berelson, R. Douglas, and D. Gorsline, 2000. Increased dissolved oxygen in Pacific intermediate waters due to lo wer rates of carbon oxidation in sediments. Nature, 407 (6802): 367-370. Stott, L.D., T. Bunn, M. Prokopenko, C. Mahn, J. Gieskes, and J.M. Bernhard, 2002. Does the oxidation of methane leave an isotopic fingerprint in the geologic record? Geochemistry Geophysic s Geosystems, 3(2), 10.1029/2001GC000196, 2002. Valentine, D.L., D.C. Blanton, W.S. Reeburgh, and M. Kastner, 2001. Water column methane oxidation adjacent to an area of active hydrate di ssociation, Eel River Basin. Geochimica et Cosmochimica Acta, 65 (16): 2633-2640. Wallman, K., P. Linke, E. Suess, G. Bohr mann, H. Sahling, M. Schlter, A. Dahlmann, S. Lammers, J. Greinert, and N. V on Mirbach, 1997. Quantifying fluid flow, solute mixing, and biogeochemical turnover at cold vents of the eastern Aleutian subduction zone. Geochimica et Cosmochimica Acta, 61: 5209-5219. Walton, W.R., 1952. Techniques for recognit ion of living foraminifera. Cushman Foundation for Foraminiferal Research, 3 (2): 56-60. Wefer, G., P.M. Heinze, and W.H. Berger, 1994. Clues to ancient methane release. Nature, 369: 282. Whiticar, Michael J., 1999. Carbon and hydr ogen isotope systematics of bacterial formation and oxidation of meth ane. Chemical Geology, 161: 291-314. Williams, David, A. Duncan, A. Backherms, E.M. Perez, A.E. Rathburn, J.B. Martin, S. Day, J. Gieskes, C. Mahn, and W. Ziebes 2002. Stable isotopic compositions of living methane seep foraminifera: Applications for paleoceanography. GSA Abstracts with Programs, 34 (6): 31.

PAGE 119

108 BIOGRAPHICAL SKETCH Shelley Day was born December 30, 1976 in Boynton Beach, Florida. She graduated from the University of Florida in August of 2000, with a Bachelor of Science degree in geology and a minor in chemistr y. She continued her education at the University of Florida, where she received her Master of Science degree in May 2003.


Permanent Link: http://ufdc.ufl.edu/UFE0000672/00001

Material Information

Title: Documenting dodern and ancient methane release from cold seeps using deep-sea benthic foraminifera
Physical Description: Mixed Material
Creator: Day, Shelley Anne ( Author, Primary )
Publication Date: 2003
Copyright Date: 2003

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0000672:00001

Permanent Link: http://ufdc.ufl.edu/UFE0000672/00001

Material Information

Title: Documenting dodern and ancient methane release from cold seeps using deep-sea benthic foraminifera
Physical Description: Mixed Material
Creator: Day, Shelley Anne ( Author, Primary )
Publication Date: 2003
Copyright Date: 2003

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0000672:00001


This item has the following downloads:


Full Text











DOCUMENTING MODERN AND ANCIENT METHANE RELEASE FROM COLD
SEEPS USING DEEP-SEA BENTHIC FORAMINIFERA















BY

SHELLEY ANNE DAY


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA


2003































Copyright 2003

BY

SHELLEY ANNE DAY















ACKNOWLEDGMENTS

This research was funded by NOAA-NURP Grant numbers UAF98-0043 and

FP007222. There are many people I wish to thank for their help and support on this

project. First, I would like to thank my advisor, Dr. Jonathan Martin, for providing me

with this research opportunity and his invaluable guidance and editorial assistance. I

would also like to thank my other committee members, Dr. Anthony Randazzo, Dr.

David Hodell and Dr. John Jaeger, for their time and advice. I thank Anthony Rathburn

and Elena Perez for contributing live foraminifera to this study, as well as assisting in

identifying fossil foraminifera. In addition, I would like to thank Joris Gieskes for

contributing pore water solute data. I thank Jason Curtis for his endless assistance in the

stable isotope lab. Finally, I would like to thank my family for providing me with

support and guidance throughout my life.
















TABLE OF CONTENTS
page

A C K N O W L E D G M E N T S ......... .................................................................................... iii

LIST OF TABLES ......... .... ........ .... .... ...... ........... ..... ..... vi

L IST O F F IG U R E S .... ...... ................................................ .. .. ..... .............. vii

A B ST R A C T .......... ..... ...................................................................................... x

CHAPTER

1 IN TR OD U CTION .................. ............................. ....... ...... .............. .

The Correlation between Climate and M ethane ................ ................... ............... 2
Methane and the Stable Isotopic Composition of Benthic Foraminifera........................ 6
Pore-water Chemistry, Vital Effects, and Foraminiferal Composition.................. 7
D iagenesis ..................................... ................................. .......... 8
O bjective/Scope of R research ........... ..................................................... .............. 9
Study A areas ............... ........... .......................... ............................ 10
M o n terey B ay .................. .................................. ................. 10
Eel River ............................................. 12


2 M E T H O D S ................................................................15

Field Sampling ......... ...... ....... ... ................ ......... 15
M onterey B ay............................................ 15
E el R iver ......................................................... .............. 17
Foraminiferal Preparation and Analyses................................. ..... 17
Live Foram inifera Preparation ................................................................... 17
The Rose Bengal Staining Technique ......................................... ..... ...... 18
Fossil Foraminifera Preparation .............................................. ............. 20
Foraminiferal Isotope Analyses .................................. ........... 20
Pore-w ater D IC A analysis ............................................... 21
Carbon Isotopes............................. ........... .............. 21
Pore W after Solutes ... ................................ ......... ............................. 22
SE M A n aly sis ................................................................... 2 2









3 R E SU L T S ....................................................... 24

P ore F lu id G eoch em istry .............................................................................................. 24
Monterey Bay........................................ 24
E el R iv er ........................................ ......... ......................... ..... 2 7
Stable Isotopic Signatures of Foraminiferal Carbonate.................................... 30
Monterey Bay...... ................................................................. 30
C a rb o n iso to p e s .......................................................................................... 3 0
Oxygen isotopes ............. .. ............. .......... ...... ....................... 36
E e l R iv e r ................................................................................................................ 3 6
C arbon isotopes................................................... 36
Oxygen isotopes ......................... ................................ .. 40
Scanning Electron Microscope (SEM) Micrographs................... .............................. 44


4 D ISC U S SIO N ...........................................................................48

The Effects of Methane on Pore Water Composition.............................................. 48
Pore Water, Methane, and the Isotopic Composition of Foraminiferal Tests........ 50
Diagenesis as a Contributing Factor to Isotopically Light Foraminiferal
C arb on ate ................... .................. ....................... .... .............. ...... 5 1
D iagenesis in the Eel River Basin...................................................... .............. 54
Stable Isotopic Com positions ................................................. ......................... ... 58
The Variation in Foraminiferal Carbon Isotopes ............................... ................. 58
The Relationship between Methane, Pore Water 613C, and Foraminiferal
C arbonate ................................... .... .... ... .... ...................... 61
A Comparison of the Isotopic Composition of Seep and Non-seep Foraminifera 63
Foram iniferal 6180 Com positions...................................................... ................ 69
A Comparison of Foraminiferal Oxygen Isotopes from Seep and Non-seep Sites 71


5 C O N C L U SIO N S ....... .......................................................................... ....... ...... .. 74

APPENDIX

A PORE W ATER CHEM ISTRY ......................................................... ............... 77

B FORAMINIFERAL ISOTOPE DATA.................................. .....................................82

C SEM PHOTOMICROGRAPHS .............................................................................95

L IST O F R EFER EN CE S ......... .................................... ........................ ............... 102

B IO G R A PH IC A L SK ETCH .................................................................. ...............108















LIST OF TABLES


Table page

1-1. A list of the amount of organic carbon (g) stored in the various reservoirs ............4

1-2. Some of the similarities and differences between the Monterey Bay and the Eel
R iver basin. .........................................................................14

2-1. A listing of cores collected from Monterey Bay and their designated use ..............16

2-2. The location and designated use of Eel River cores ..............................................17

2-3. List of terms used in this paper to describe foraminifera. ........................................19

2-4. Foraminifera used for SEM analysis. ............................................. ............... 23

3-1. The 613CDIC values of supernatant fluids taken from the tops of cores designated
for pore w ater analyses................................................ .............................. 27

3-2. A statistical comparison of Monterey Bay foraminifera...........................................31

3-3. A statistical comparison of fossil (?) foraminifera from Eel River Basin ...............40

4-1. A comparison of the mean 613C and 6180 values of U. peregrina from Invertebrate
Cliffs (1780 PC30), Clam Flats (1781 PC31), and Eel River (2052 LC2, LC4,
an d L C 5 )...................................................... ................ 5 4

4-2. A comparison of the mean 613C values and standard deviations of live foraminifera
from Clam Flats (PC31) and Invertebrate Cliffs (PC30).......................................62















LIST OF FIGURES


Figure page

1-1. Map showing the location of Monterey Bay cold seeps, including Clam Flats and
Invertebrate Cliffs, which were sampled in this study............................... 11

1-2. A map of the northern California margin showing a portion of the Eel River Basin,
which w as sam pled for this study .........................................................................13

2-1. A picture of the seepage area sampled from Invertebrate Cliffs located at
approximately 955 meters water depth (Dive 1780)........................................ 16

3-1. Pore water calcium profiles for Monterey Bay clam beds (Dive 1780 PC79,
Invertebrate Cliffs and Dive 1781 PC80, Clam Flats) ........................................25

3-2. Pore water sulfide (HS-) profiles for Monterey Bay clam beds (Dive 1780 PC79,
Invertebrate Cliffs and Dive 1781 PC80, Clam Flats) ........................................25

3-3. Pore water alkalinity profiles from Monterey Bay clam beds (Dive 1780 PC79,
Invertebrate Cliffs and Dive 1781 PC80, Clam Flats) ........................................26

3-4. The 613CDIC profile of pore water from Monterey Bay clam beds (Dive 1780 PC79,
Invertebrate Cliffs and 1781 PC80, Clam Flats)...........................................26

3-5. Calcium pore water profiles for Eel River Dive 2052: PC16 (bacterial mat), PC8
(clam bed), and PC19 (bubble site)........._. ........... ................... ............... 28

3-6. Pore water sulfide profiles for Eel River Dive 2052: PC16 (bacterial mat), PC 8
(clam bed) and PC19 (bubble site). ... ................... ....................... ............... 28

3-7. Sulfate ion pore water profiles from Eel River Dive 2052: PC16 (bacterial mat),
PC 8 (clam bed) and PC19 (bubble site)................................... ............... 29

3-8. Pore water alkalinities for Eel River Dive 2052: PC8 (clam bed), PC16 (bacterial
m at), and PC 19 (bubble site). ........................................ ........................... 29

3-9. Pore water 613CDIC for Eel River Dive 2052 PC16 (bacterial mat), PC8 (clam bed)
and PC19 (bubble site).............. .... ................... ............ ............... 30

3-10. Dive 1780 HPC5 and PC30 (Invertebrate Cliffs clam bed) Uvigerinaperegrina
613C vs. depth ............. ...... ... .... ...... ...................... 32

vii









3-11. Dive 1780 HPC5 and PC30 (Invertebrate Cliffs clam bed) Epistominellapacifica
613C vs. depth.............. .... ............ .... ...... ... ................... 32

3-12. Dive 1780 HPC5 and PC30 (Invertebrate Cliffs clam bed): Bulimina mexicana
613C vs. depth................................................... ........ ...... .............. 33

3-13. Dive 1780 (Invertebrate Cliffs clam bed) HPC5 and PC30 Globobulimina
pacifica 613C vs. depth ........... ............... .......... ............... ............... 33

3-14. Dive 1781 PC31 (Clam Flats clam bed) Uvigerinaperegrina 613C vs. depth........35

3-15. Dive 1781 PC31 Clam Flats (clam bed): Epistominella pacifica, Bulimina
mexicana, Globobulimina pacifica, and Planulina species 613C vs. depth ..........35

3-16. Dive 1780 HPC 5 and PC30 (Invertebrate Cliffs clam bed) Epistominella
p acifica 6180 vs. depth.................. ............................................ ............... 37

3-17. Dive 1780 HPC5 and PC30 (Invertebrate Cliffs clam bed) Bulimina mexicana
6180 vs. depth. .......................................................................37

3-18. Dive 1780 (Invertebrate Cliffs clam bed) HPC5 and PC30: Uvigerinaperegrina
6 180 v s. d ep th ................................................. ................. 3 8

3-19. Dive 1780 (Invertebrate Cliffs clam bed) HPC5 and PC30 Globobulimina
p acifi ca 61 0 vs. depth.................. ............................................ ............... 38

3-20. Dive 1781 PC31 (Clam Flats clam bed) Uvigerinaperegrina 6180 vs. depth........39

3-21. Dive 2052 long core 5 (bacterial mat): Uvigerinaperegrina and Epistominella
pacifica 613C s. depth ............................................................. ............... 41

3-22. Dive 2052 Long core 4 (clam bed): Epistominellapacifica and Uvigerina
peregrina 613C vs. depth .......................................................... ............... 41

3-23. Dive 2052 Long core 2 (bubble site): Uvigerinaperegrina, Epistominella
pacifica, and Bulimina mexicana 613C vs. depth ...............................42

3-24. Dive 2052 long core 2 (bubble site): Uvigerinaperegrina, Bulimina mexicana
and Epistominellapacifica 6180 vs. depth. ................................. ..................42

3-25. Dive 2052 long core 4 (clam bed): Epistominellapacifica and Uvigerina
p eregrina 6180 vs. depth.............................................. ............. ............... 43

3-26. Dive 2052 Long Core 5 (bacterial mat): Uvigerinaperegrina and Epistominella
p acifica 6180 vs. depth .................................................. ........................... 43









3-27 (a, b). A scanning electron micrograph of an Uvigerinaperegrina from Monterey
Bay's Invertebrate Cliffs clam bed. (a) An overall shot of the test. (b) A close
up of the test from the region identified in (a). ................................................. 45

3-28. A scanning electron micrograph of an Epistominellapacifica from Monterey
Bay's Invertebrate Cliffs clam bed. (a). An overall view of the test. (b). A
close-up of the test from the region identified in (a). ..........................................46

3-29 (a,b). A scanning electron micrograph of a U. peregrina from Eel River's long
core 4 (clam bed). (a) An overall view of the test. (b). A close-up of the region
id en tifie d in (a).................................................................. 4 7

4-1. A plot of the saturation indices (SI) versus depth for the bubble site (PC19, which
corresponds to the foraminifera from long core 2). ....................... ...............56

4-2. A plot of the saturation indices (SI) versus depth for PC8 (clam bed, which
corresponds to the foraminifera from long core 4). ....................... ...............56

4-3. A plot of the saturation indices (SI) versus depth for PC 16 (bacterial mat, which
corresponds to the foraminifera from long core 5). ....................... ...............57

4-4(a, b). The average A613C and standard deviation (c) of U. peregrina from
Invertebrate Cliffs (1780 PC30) and Clam Flats (1781 PC31) compared to values
reported in the literature. (a). Actual bottom water d13C is not used; instead,
the supernatant fluid from the core tops is substituted for bottom water (See text
for discussion). (b). An estimated bottom water value of-0.3%o is used for the
calculation of the average A613C from Clam Flats and Invertebrate Cliffs. Note
the difference in the scale of the x-axis from (a). ................................................67

4-5(a, b). The average A613C and standard deviation of U. peregrina from Eel River's
Long core (LC) 4 (clam bed) and LC5 (bacterial mat), compared to those
reported in the literature. (a). LC4 and LC5 are plotted using 613CDIC values
obtained from supernatant fluid (see text for discussion). (b) LC4 and LC5 are
replotted using Rathburn et al.'s (2000) bottom water 613CDIC value....................68

4-6. A 6180 comparison of live and fossil conspecific foraminifera from Clam Flats
(178 1 P C 3 1) ....................................................................... .. .... ... .. 69

4-7. A plot of the A6180 values of U. peregrina from Invertebrate Cliffs (1780 PC30)
and Clam Flats (1781 PC31) relative to those values reported in the literature ....72

4-8. A plot of the A6180 values of U. peregrina from Eel River (2052) LC5 (bacterial
mat), LC4 (clam bed) and LC2 (bubble site) relative to those values reported in
th e literate re.. .........................................................................73















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

DOCUMENTING MODERN AND ANCIENT METHANE RELEASE FROM COLD
SEEPS USING DEEP-SEA BENTHIC FORAMINIFERA


By

Shelley Anne Day

May 2003


Chair: Jonathan Martin
Major Department: Geological Sciences

Methane, which is a potent greenhouse gas and a highly reduced form of carbon,

is a minor component of the atmosphere; however, large amounts of methane are stored

in continental margin sediments as a component of pressure and temperature sensitive gas

hydrates. Dissociation of these hydrates and the release of methane, which could have

important climatic implications, have been inferred in the past based on the isotopic

composition of fossil foraminifera in prior paleoceanographic studies. Little analogous

data from modem seep sites exist to document the significance of released methane on

foraminiferal isotopic composition.

Methane is commonly released from cold seep environments, which are ideal

settings to investigate the relationship between methane and the isotopic composition of

foraminifera. For this study the stable isotopic compositions of living (Rose Bengal

stained) and fossil benthic foraminifera from active seepage sites in Monterey Bay (1000









m) and the Eel River Basin (-520 m) on the California margin were used along with pore

water chemistry to assess the effects of methane on foraminiferal carbonate.

Live and fossil benthic foraminifera from these seep sites were found to have

carbon isotopic compositions that are more variable than the same species of foraminifera

previously measured from non-seep sites on the California and North Carolina margins.

In general, the carbon isotopic values of the seep foraminifera were similar to or up to a

few per mil lighter than the isotopic values of foraminifera found in non-seep sites. The

isotopic values of the seep foraminifera, however, are far from equilibrium with the

ambient dissolved inorganic carbon pool, which has carbon isotopic values as light as

-45%o in the upper 5 cm of the core. This disequilibrium could indicate that the

foraminifera have specific microenvironments where calcification takes place, possibly

near the surface or near burrows where seawater DIC (613CDIC approximately 0%o) would

contribute more to the DIC pool. The isotopic composition of the DIC, which would

vary with the episodic seepage of methane, does create variability in foraminiferal carbon

isotope values.

In contrast with the large disequilibrium observed among foraminifera and

613CDIC values in Monterey Bay, large negative carbon isotopic excursions, as light as

-23%o, are seen in Eel River foraminifera. These light isotope ratios appear to result from

postmortem precipitation of authigenic carbonate, which is in equilibrium with the

613CDIC, on the tests. Faster seepage rates or more profuse seepage at Eel River could

cause authigenic carbonate precipitation to occur in Eel River and not Monterey Bay.

Therefore, variability in the isotopic composition of conspecific foraminifera appears to

be a better indication of methane release than absolute isotopic values.














CHAPTER 1
INTRODUCTION



Methane, which contains a highly reduced form of carbon, plays an important role

in many of the biological and geochemical processes on Earth. Although methane is a

minor component of the atmosphere, it has nevertheless received considerable attention

due to its potential as a powerful greenhouse gas. The realization that large amounts of

methane are stored subaqueously, frozen as "gas hydrates" within a temperature and

pressure sensitive solid framework of water molecules, has led to suggestions that

methane may have played an important role in the Earth's climatic history (Wefer et al.,

1994; Dickens et al., 1995; Kennett et al., 1996). For instance, the abrupt warming which

characterizes the first few decades of interglacials and interstadials is accompanied by

rapid increases in atmospheric methane (Severinghaus et al., 1998).

Gas hydrates are temperature and pressure sensitive; therefore, the dissociation of

gas hydrates would result from warmer climatic conditions and warmer waters or lower

sea levels. Methane released from subaqueous gas hydrates could diffuse up through the

sedimentary column, be oxidized by bacteria and contribute bicarbonate to the dissolved

inorganic carbon pool and possibly be incorporated into foraminiferal tests. Using

foraminifera as a proxy, Kennett et al. (2000) proposed that changes in thermohaline

circulation over the past 60,000 years in the Santa Barbara Basin resulted in fluctuations

in water temperature. In turn, variable water temperatures resulted in the periodic

destabilization of gas hydrates, which contributed isotopically light carbon and heavy

1








2
oxygen to planktonic and benthic foraminifera living within the Santa Barbara Basin

(Kennett et al., 2000).

If the isotopic values obtained from fossil foraminifera preserve ancient pore-

water conditions, then the stratigraphic variation in these values would provide a record

of methane seepage. In addition to the anomalously negative carbon isotopic

compositions of fossilized benthic foraminifera suggested to result from gas hydrate

dissociation (Kennett et al., 1996; 2000; Dickens et al., 1995; Wefer et al., 1994), diverse

carbon isotopic compositions are reported for live and fossil benthic foraminifera

inhabiting methane seep sites (Sen Gupta and Aharon, 1994; Rathburn et al., 2000).

These recent studies (Rathburn et al., 2000; Williams et al., 2002) question the validity of

a direct link between methane seepage and a light 613C foraminiferal test value. Seepage

instead may be inferred based on the heterogeneity of carbon isotope values and the

similarity of oxygen isotope values among numerous tests collected from identical depths

(i.e., times of deposition). There is, however, a scarcity of analogous data available from

modern (living) foraminifera to evaluate this hypothesis. Therefore, it is the intent of this

work to show that the magnitude of the 613C of benthic foraminifera (live and fossil)

alone does not reliably indicate methane and associated dissolved inorganic carbon (DIC)

venting from marine sediments; however, when numerous foraminifera from areas of

seepage are analyzed, methane venting is manifested in the heterogeneity of foraminiferal

carbon isotope values among coexisting conspecific individuals.

The Correlation between Climate and Methane

In recent years, research focusing on the causes of global climate change,

particularly global warming, has intensified. Greenhouse gases, such as carbon dioxide








3
and methane, which contribute to the global warming of the earth, are of particular

concern. The effect that greenhouse gases have on the atmosphere not only depends on

their concentrations but also on their residence times in the atmosphere and the width of

their absorption bands. As a result of methane absorbing radiation in the wavelength band

between 8000-12000 nm, where carbon dioxide is not an effective absorber, 1 kg of

methane has the potential to absorb 21 times the infrared radiation as 1 kg of carbon

dioxide (Houghton et al., 1990). Thus, the carbon cycle and climate change could be

significantly affected by the release of methane. One of the major reservoirs of methane

is believed to be in gas hydrates formed and trapped in continental margin settings

(Kvenvolden, 1988).

Natural gas hydrates are formed when a rigid framework of water molecules

freezes in the presence of sufficient natural gases; the water crystallizes in a cubic lattice

and traps the gas molecules (MacDonald, 1990). Methane is the dominant gas found in

most oceanic gas hydrates, representing greater than 98% of the total gas, although

ethane, carbon dioxide, and hydrogen sulfide may also be significant in some regions

(Dickens, 2001). According to Kvenvolden (1988), the amount of methane currently

stored within subaqueous gas hydrates may be in excess of 1019 g of methane carbon.

This estimation exceeds the amount of methane stored in all other reservoirs combined

(Table 1-1).

The stability of gas hydrates is a function of temperature, pressure, salinity, and

gas concentration, with hydrates commonly forming in the oceans where water depths are

between 300 and 2000 meters and temperatures are less than 50 C (Kvenvolden, 1988).

Hydrates form rapidly, within minutes, both in free seawater and in sediments based on








4
experiments conducted in the waters of Monterey Bay (Brewer et al., 1997); similarly,

the hydrates dissociated rapidly during the experiment, first with bubbles being emitted

from the sediments and then with continuing gas expansion, the dissociating hydrates

ruptured the cylinders housing the experiment (Brewer et al., 1997). In natural settings,

once the gas hydrates are no longer within the stability field, for example by changing

ambient conditions (such as a pressure decrease due to the removal of overburden), the

gases may migrate upward through the sedimentary column and reach the seafloor,

depending upon the texture and porosity of the sediment. Such emissions of methane

(and other gases) at ambient seafloor temperatures are often termed cold seeps.

Table 1-1. A list of the amount of organic carbon (g) stored in the various reservoirs.
Reservoir Amount of organic carbon (g)

Gas hydrates >1019
All fossil fuel deposits 5-1018
Terrestrial soil, detritus, and peat 1.96-1018
Marine dissolved materials 9.8-1017
Terrestrial biota 8.3-1017
Atmosphere 3.6-1015
Marine biota 3-1015
Data from Kvenvolden (1988).

The methane emitted from cold seeps may be either biogenic or thermogenic in

origin. Biogenic methane is produced in shallow sediments as a result of the microbial

degradation of organic matter. Thermogenic methane results from the thermochemical

dissociation of organic matter at high temperatures and depths (2-3 km). The two sources

may be distinguished based on the carbon isotopic signature of the methane. In general,

microbially produced methane is isotopically lighter than thermogenic methane, which is

characterized by 613C values ranging from -50 to -20%o (Whiticar, 1999). Biogenic








5
methane typically exhibits 613C values less than -50%o (Whiticar, 1999). Regardless of

its source, the 613C of methane is isotopically lighter than the inorganic forms of carbon

dissolved in seawater, which have a 613C of approximately 0%o PDB. Therefore, if

isotopically light methane reaches the sediment-water interface, it would decrease the

613C of DIC after being oxidized in the pore waters. These light isotope ratios are

retained in the authigenic carbonate minerals that form from the isotopically light DIC;

however, it is unknown whether benthic foraminifera preserve these signatures. Inferring

seepage based on benthic foraminiferal carbonate rather than authigenic carbonate would

be valuable, as benthic foraminifera are characterized by a relatively short lifespan (on

the order of years) and would provide a stratigraphic component, which may provide

clues to the longevity of seepage.

Today the majority of natural atmospheric methane is produced as a result of

bacterial decomposition in wetland environments (Blunier, 2000). It has been proposed,

however, that during former periods of rapid climate change, large quantities of methane

were released to the oceans and atmosphere as a result of the dissociation of gas hydrates

(Wefer et al., 1994; Dickens et al., 1995; Kennett et al., 1996; 2000). For instance, off

Peru, Dickens et al. (1995) attributed a -2 to -3%o shift in benthic foraminiferal 613C and

6180 in less than 104 years (during the late Paleocene) to the dissociation of hydrates,

which were thought to have destabilized due to a 40C increase in bottom water

temperature (Dickens et al., 1995). Additionally, in the Santa Barbara Basin, Kennett et

al. (2000) attributed a large carbon isotopic excursion to hydrate destabilization; this

excursion was characterized by interstadial benthic foraminifera being lighter by up to

4%o relative to stadial foraminifera.








6
Methane and the Stable Isotopic Composition of Benthic Foraminifera

The flux of methane into the water column, and eventually the atmosphere, would

be much greater were it not for the bacterial consumption of methane, which catalyzes

inorganic methane oxidation. Methane that is migrating upward in the sedimentary

column may be oxidized by either aerobic or anaerobic bacteria, known as

methanotrophs, depending on the availability of free oxygen. Aerobic methanotrophs are

able to use methane as an energy source through the production of carbon dioxide; these

organisms are found living within the pores of sediments and in the tissues of benthic

fauna associated with cold seeps (Cavagna et al., 1999). Alternatively, anaerobic

methanotrophs interact with another microbial group, the hydrogen-oxidizing-sulfate-

reducers, in order to drive the metabolic transformation of methane into bicarbonate (and

sulfate into hydrogen sulfide) (DeLong, 2000). Another bacterial process occurs in the

water column, where free-living methanotrophs oxidize methane; these organisms create

carbon dioxide plumes, which when diluted with normal bottom waters can deplete the

613CDIC by 4.5%o (Aharon et al., 1992; LaRock et al., 1994).

The production of bicarbonate due to the activity of methanogens has a profound

effect on the pore-water chemistry and possibly the isotopic composition of benthic

foraminifera. Studies have shown that foraminifera found within seepage areas have

more negative 613C signatures than foraminifera found within areas unaffected by

seepage (Sen Gupta and Aharon, 1994). For instance, fossil benthic foraminifera from

venting sites in the Gulf of Mexico had anomalously depleted 613C values (as light as

-3.6%o), whereas fossil benthic foraminifera from non-seep sites displayed 613C values as

heavy as 0.4 %o (Sen Gupta and Aharon, 1994).








7
Pore-water Chemistry, Vital Effects, and Foraminiferal Composition

In addition to ambient pore-water chemistry, taxon-specific "vital" effects and

microhabitat effects also influence the geochemistry of benthic foraminiferal test

carbonate (McCorkle et al., 1990). Vital effects, which are a result of physiological

processes, can be divided into two categories: metabolic isotope effects and kinetic

isotope effects. Metabolic effects result from the incorporation of respired, isotopically

light carbon dioxide into the foraminiferal test, which results in a depletion of 13C in the

test (Grossman, 1987), whereas kinetic effects occur during periods of rapid chamber

formation, when lighter isotopes of carbon and oxygen are preferentially incorporated

(McConnaughey, 1989).

Microhabitat effects can be attributed to foraminifera living within the sediment at

specific depths, where variations in the pore-water DIC may influence the 613C of the

test. For instance, infaunal taxa display consistently lower 613C values than epifaunal

taxa. Additionally, deep-dwelling species are consistently more depleted in 13C than

either shallow infaunal species or epifaunal species as a result of the decrease in the 613C

of pore-water DIC with sediment depth (McCorkle et al., 1990). However, despite these

recognized trends, for any particular species that displays a broad depth range within the

sediment, the variability of 613C values is low, despite the depth at which the

foraminiferan is found (Rathburn et al., 1996). While it has been proposed that the

isotopic uniformity within a given species results from microenvironments, food

preferences, or growth within a narrow depth range, the influence of pore-water

chemistry on the isotopic composition of foraminiferal tests remains debatable (Rathburn

et al., 1996; 2000).









Diagenesis

In addition to influencing the isotopic composition of live foraminifera, pore

water chemistry may alter the isotopic composition of fossil foraminifera through

diagenesis; contamination by biogenic calcite or post mortem calcite overgrowths is

another plausible explanation for the negative 613C values observed in some fossil

foraminifera. In marine settings, a consortium of bacteria produces bicarbonate while

oxidizing organic matter and methane. Production of bicarbonate is enhanced at seep

settings, where large quantities of methane are able to support a large population of

bacteria. Carbonate precipitation may be enhanced by the production of bicarbonate,

which would drive the reaction

Ca2+ + 2HC03- < CaCO3 + H20 + CO2 (1)

to the right. Additionally, carbonate precipitation should be enhanced at the

sulfate/methane boundary where localized anaerobic methane oxidation may produce a

sharp increase in the alkalinity of the pore water (Blair and Aller, 1995).

Authigenic carbonate is present at Eel River and Monterey Bay seep sites (Stakes

et al., 1999; Rathburn et al., 2000; this study). Thin sections of authigenic carbonates

from Monterey Bay often contained pyrite framboids encased in high-Mg calcite filling

the chambers of the U. peregrina, which are composed of low-Mg calcite (Stakes et al.,

1999). Pristine U. peregrina tests, however, were also found in a groundmass of high-

Mg calcite (Stakes et al., 1999). It is unknown whether fine-grained authigenic

carbonates are being precipitated within the chambers of fossil foraminifera in unlithified

sediments, such as those analyzed for this study. Although foraminifera designated for

isotopic analysis are microscopically examined for calcite contamination and cleaned








9
ultrasonically, this technique may not detect authigenic carbonate grains that may be

present inside some of the chambers of the test. If authigenic carbonate was

contaminating foraminiferal tests, carbon and oxygen isotopic compositions would be

expected to be widely variable in a large population of analyzed foraminifera.

The problem of diagenetic alteration can be approached through thermodynamics,

by calculating saturation states. In thermodynamic modeling the chemical analysis of

water is used to calculate the distribution of aqueous species. Saturation Indices (SI)

determine whether a mineral should dissolve or precipitate. A positive saturation index

for a mineral indicates that the pore water is oversaturated with respect to that mineral

and thermodynamically, precipitation is favored. A negative value indicates that the pore

water is undersaturated and dissolution of that mineral is thermodynamically favored.

This technique assumes that the pore water composition has not changed from the time of

deposition. With burial, however, the pore water should become increasingly saturated

with respect to calcite through the diagenetic pathway shown by reaction (1).

Objective/Scope of Research

The primary objectives of this study are twofold: (1) to determine whether benthic

foraminifera reliably record modern and historic sites of methane and associated DIC

venting from cold seeps and (2) to determine how this record may be manifested in the

isotopic composition of the foraminifera. While investigating this broad objective, the

following more specific questions are addressed:

1. What is the relationship between the isotopic signature of foraminiferal
carbonate and the isotopic signature of ambient pore-water in methane
seep environments? What variations exist in the isotopic signatures of
individual species within and between different seep settings? How do the
stable isotopic signatures of benthic foraminifera from cold methane seeps
compare to those generated in non-seep environments?








10
2. Does methane seepage create a distinct isotopic signature in benthic
foraminiferal tests that may serve to map the extent and history of methane
fluxes? If so, can isotopic signatures of fossil benthic foraminifera be
used to identify the longevity and the extent of venting?

3. Within a given methane seep environment, do different species of
benthic foraminifera have different carbon isotopic compositions? Are
isotopic differences enhanced between epifaunal and infaunal species in
methane seep environments?

Along with analyzing fossil benthic foraminiferal tests, this study also examines

live (stained) deep-sea benthic foraminifera to determine the relationship between

methane release and test composition, isotopic variability within a given species, and the

variations in test composition generated by seep and non-seep environments. McCorkle

et al. (1990) analyzed the isotopic composition of live foraminifera from both the Atlantic

and Pacific Oceans. Their main objective, however, was to identify the relationship

between microhabitats and the carbon isotopic composition of foraminiferal tests. One

previous study published by Rathburn et al. (2000) researched the relationship between

live foraminifera and methane seepage off the slope of the Eel River, California.

However, the limited number of live foraminiferal specimens, the lack of 613CDIC

analyses, and the limited geographic coverage has left unanswered questions regarding

methane release and foraminiferal test composition.

Study Areas

Monterey Bay

Monterey Bay provides an ideal location to investigate methane release from cold

seeps (Figure 1-1). The bay is underlain by the Salinian block, which is an allochthonous

granodiorite basement rock that has moved northward during the past 21 million years of

activity along the San Andreas Fault (Page, 1970). The Salinian granodiorite, along with

the San Simeon block, are the two major tectonic provinces within the bay (Greene et al.,








11
1993). The Miocene Monterey Formation, which along with its equivalents, are organic-

rich marine sediments, the Late Miocene Santa Cruz mudstone, and the Miocene-

Pliocene Purisma sandstone crop out offshore and along canyon walls (Greene et al.,

1989). Numerous faults, including the San Gregorio and Monterey Bay Fault Zones,

dissect the bay creating a dynamic environment characterized by fluid flow (Orange et

al., 1999). Cold seeps have been found both as isolated communities along these major

faults (Barry et al., 1996) or among isolated zones of active mud volcanism (Martin et al.,

1997). Pore-water analyses obtained from push cores located within the cold seeps

revealed methane concentrations up to 841 [LM (Barry et al., 1997).

_____ 1L ':'_________________I- 3f___________t T ____________l "___________1 1 ___


12Z 12Z 12Z I1 12Z Vy 121 'u
Figure 1-1. Map showing the location of Monterey Bay cold seeps, including Clam Flats
and Invertebrate Cliffs, which were sampled in this study (taken from
http://www.mbari.org/benthic/coldseeploc.htm).
At present in Monterey Bay, there are no known exposures of clathrates; however,

discrete cold seeps sampled in the bay contain gaseous hydrocarbons and high molecular








12
weight aliphatic and aromatic hydrocarbons (Lorenson et al., 2002). Since no clathrates

have been detected in Monterey Bay, fluid flow is instead likely the result of tectonic

compression, with interstitial fluids migrating upward in the sedimentary column along

faults (Lorenson et. al, 2002).

The methane seeping from Monterey Bay is likely to come from one of two

sources. The organic-rich Monterey Formation provides a thermogenic source for the

methane (Martin et al., 1997; Stakes et al., 1999), whereas the microbial reduction of

carbon dioxide below the sulfate reduction zone provides a biologic source. Stakes et al.

(1999) proposed that biological communities appear to be related to a deep source of

reduced carbon, rather than a surficial source, based on the spatial arrangement of the

communities. The isotopic composition of most sites however, points to a mixed origin

for the methane (Martin et al., 1997).

Eel River

The Eel River Basin (Figure 1-2), which is part of a late Cenozoic forearc,

extends approximately 210 km, from Cape Mendocino, California to Cape Sebastian,

Oregon; the basin is bounded by the Cascadia subduction zone to the west, and the

Mendocino Fracture Zone to south (Burger et al., 2002). The structural evolution of the

basin continues today, as the convergence of the Gorda and North America plates

continues; additionally, much of the deformation in the southern portion of the basin

results from the continuing northward migration of the Mendocino Triple Junction

(Furlong and Govers, 1999).

Although there are some similarities shared by Monterey Bay and the Eel River

Basin, one major difference is the presence of gas hydrates in the Eel River Basin (Table

1-2). Kvenvolden and Field (1985) mapped the distribution of hydrates in the Eel River








13
basin using the location of the bottom-simulating reflector (BSR). The BSR is a

characteristic seismic reflection, which results from the strong impedance contrast

between hydrate bearing sediments and gas-filled pore spaces. Although BSRs may also

result from changes in acoustic velocity resulting from diagenesis, the BSRs in the Eel

River Basin are attributed to gas hydrates since they occur at the base of the gas hydrate

stability field; additionally, the BSRs are found deeper in the sediment as water depth

increases, which is characteristic of a gas hydrate, since diagenetic BSRs tend to become

shallower as water depth increases (Kvenvolden and Field, 1985). Additionally, the

recovery of hydrates containing biogenic gas from shallow cores, less than 6 meters deep,

taken from areas showing bottom-simulating reflectors confirms both the indirect

geophysical evidence and the geologic observations, such as active methane venting from

sediments, for the presence of gas hydrates in the basin (Brooks et al., 1991).

12 124 30' 124" W



Study /ini"l
area

...Mad River






40' 30' ,

Figure 1-2. A map of the northern California margin showing a portion of the Eel River
Basin, which was sampled for this study. Adapted from Rathburn et al. (2000).








14
Table 1-2. Some of the similarities and differences between the Monterey Bay and the
Eel River basin.
Monterey Bay Eel River
Tectonics Right-lateral strike slip Convergent
Similar to Eel River, with Similar to Monterey Bay,
Foraminiferal common species including U. with common species
Assemblages peregrina and E. pacifica including U. peregrina and
E. pacifica
Gas Hydrates None found Abundant
Average 2.2 mm/yr for Monterey Bay 4 mm/yr for Eel River
Sedimentation Rate shelf* shelf**
*Lewis et al (2002) **Sommerfield and Nittrouer (1999)














CHAPTER 2
METHODS



Field Sampling

Monterey Bay

Samples from Monterey Bay were collected from two distinct sites during June of

2000. Samples from the first site were collected during Dive 1780 on June 22 from an

area termed "Invertebrate Cliffs", located at 36046.39'N 1225.08'W. These samples

were gathered using the R.V. Point Lobos and ROV Ventana in a water depth of

approximately 955 meters. Cores were taken from four distinct areas within Invertebrate

Cliffs (Table 2-1); three of these sites were located within an area influenced by methane

seepage, based on the presence of clam communities and bacterial mats. The seep areas

sampled were a whitish-gray bacterial mat, a yellow bacterial mat, and a clam

community; the area had a concentric arrangement, with clams encircling the two

bacterial communities (Figure 2-1). The last set of cores came from a reference site,

which was located south of the clam community in an area of presumed non-seepage.

Three push cores, which were 7 cm in diameter and up to 20 cm in length, were

collected from each of the four sites for the analyses of foraminifera and pore water.

Additionally, two hydraulic piston cores, which were up to 45 cm in length, were taken

for the analysis of fossil foraminifera; one core was taken in the clam community, and the

other core was taken between the two bacterial mats.









Table 2-1. A listing of cores collected from Monterey Bay and their designated use.
DIVE SITE SITE DESCRIPTION CORE DESIGNATED USE
PC67 Live faunal analyses
Whitish-gray bacterial mat P6 Lvfanaal
SPC34 Pore water geochemistry
Yellow bacterial mat PC31* Pore water geochemistry
1780 Between the two bacterial mats HPC 2 Live faunal analyses
SPC30* Faunal analyses
> Clams PC79* Pore water geochemistry
HPC5* Faunal analyses (fossil)
Reference (5 m N. of clam PC71 Live faunal analyses
bed) PC38* Pore water geochemistry
PC31* Live faunal analyses
Clam bed
Ca PC80* Pore water geochemistry
1781
11 PC30 Live faunal analyses
3 Bacterial mat
B PC28 Pore water geochemistry
PC34 Live faunal analyses
Reference (4 m. from Mat) water geochemistry
PC72 Pore water geochemistry


* Results from these cores will be presented in detail


Clams


in this thesis.


White-
gray
bacterial







Yellow
bacterial
mats


Figure 2-1. A picture of the seepage area sampled from Invertebrate Cliffs located at
approximately 955 meters water depth (Dive 1780).

On June 23, a second area, Clam Flats, located at 36044.7'N 12216.6'W, was

sampled. During Dive 1781, cores were collected from a bacterial mat located at a water









depth of approximately 1000 meters. Reference cores were collected four meters from

the bacterial mats. Live clam beds, as well as a reference area located five meters due

north of the clam bed were sampled. Once again, three push cores were taken from each

site for isotopic and faunal analyses (Table 2-1). A complete description of this site is

provided by Barry et al. (1996).

Eel River

Eel River samples were collected August 21, 2001, during Dive 2052. Four

distinct areas were visited for sampling purposes: a bacterial mat (4047.058'N

12435.729'W), a clam bed (2 m north of 4047.080'N 12435.700'W, a site marked by

active bubbling (4047.2001'N 12435.7251'W), and a reference area (4047.1717'N

12435.6970'W) (Table 2-2). The approximate water depth for all cores was 520 meters.

Table 2-2. The location and designated use of Eel River cores.
DIVE SITE SITE DESCRIPTION CORE DESIGNATED USE
Bacterial mat Long Core 5 Faunal analyses (fossil)
Bacterial mat
PC16 Pore water geochemistry
2 C s Long Core 4 Faunal analyses (fossil)
2052 0 Clams
> ________PC8 Pore water geochemistry
B Long Core 2 Faunal analyses (fossil)
SBubble site
PC19 Pore water geochemistry


Foraminiferal Preparation and Analyses

Live Foraminifera Preparation

For all sites, push cores designated for live foraminiferal analysis were vertically

subsampled at 0.5-cm increments down to 3 cm and at 1-cm intervals down to 10 cm

within the sediments. Following procedures outlined by Rathburn and Corliss (1994),

each subsample was preserved in 200 ml of 4% buffered formaldehyde; in the laboratory

65 ml of Rose Bengal stain solution was added to foraminiferal samples and allowed to









remain staining the samples for at least one week. Samples were then washed and sieved

with nested 63 and 150 |tm mesh sieves. Stained benthic foraminifera, which were

believed to be alive at the time of collection, were then wet-picked from the >150 |tm

fraction, sorted, and identified. As a convention in this paper, the use of the term "live"

will refer to Rose Bengal stained (i.e., those foraminifera containing at least one stained

chamber) foraminifera, which were presumed to be alive at the time of collection (Table

2-3). The term "fossil" will refer to those foraminifera subjected to the Rose Bengal

stain, containing no stained chambers, which were presumed to be dead at the time of

collection. Additionally, all foraminifera collected from cores not treated with Rose

Bengal stain will be referred to as fossil (?), since it is unknown whether these

foraminifera were alive or dead at the time of collection.

Foraminifera are commonly found living up to 10 cm below the seafloor

(Jorrisen, 1999). In addition, Corliss (1985) found the deeper infaunal species

Globobuliminapacifica, which is tolerant to low oxygen conditions, living at sediment

depths down to 15 cm below the seafloor. Unless associated with a burrow, shallower

infaunal foraminifera most likely are not living below 10 cm sediment depth. Live

foraminifera from Monterey Bay were not found at high abundances below 5 cm

sediment depth. All foraminifera designated for analysis were microscopically examined

and cleaned using an ultrasonic bath.

The Rose Bengal Staining Technique

The Rose Bengal technique was first introduced in 1952 by Walton; it is the most

prevalent technique in the literature pertaining to the identification of live foraminifera.

The stain functions by absorbing onto the surface of the protoplasm, staining it a bright









red. As a result of the protoplasm filling the test and inhibiting the penetration of the

stain, often only one or two of the newest chambers of the foraminifera are visibly stained

(Boltovskoy and Wright, 1976).

Table 2-3. List of terms used in this paper to describe foraminifera.
Term Definition (as used in this paper)
Those foraminifera subjected to the Rose Bengal stain, which contain at least
Live one brightly stained red or pink chamber. Believed to be alive at the time of
collection (or at least recently)
Fos Those foraminifera subjected to the Rose Bengal stain, which contain no
stained chambers. Believed to be dead at the time of collection.
Those foraminifera not subjected to the Rose Bengal stain, some of which,
Fossil (?) from the upper portion of the cores, could have been living at the time of
collection.

The manner in which Rose Bengal works has resulted in one of its major

criticisms: since the stain adheres to proteins, any algae or nematode occupying a fossil

foraminiferal test will also be visibly stained. Additionally, even after death, the

protoplasm may still absorb stain; however, the time required for the disintegration of

protoplasm appears short in oxic environments (Jorrisen, 1999). In anoxic

environments, however, the degradation of the protoplasm can take weeks or months and

theoretically tens of years and could adsorb the Rose Bengal stain during this period

(Bernhard, 1988; Corliss and Emerson, 1990).

Notwithstanding these restrictions, Rose Bengal is the most practical technique

available for dealing with large quantities of foraminifera (Rathburn et al., 2000).

Additionally, since the technique is commonly used, data are available for comparison.

Finally, unlike other stains, it is known that Rose Bengal does not affect the isotopic

signature of the foraminifera.









Fossil Foraminifera Preparation

Hydraulic piston cores and long cores designated for fossil foraminiferal analyses

were vertically subsampled at 1-cm intervals. In the laboratory, the subsamples were

sonicated (if necessary), washed and wet-sieved using nested 63 and 125 |tm mesh

sieves. Samples were washed onto filter paper and dried in the oven at 600C.

The >125 |tm fraction designated for picking was split using a microsplitter (if

the sample needed to be reduced into a manageable volume) and weighed. The

foraminifera were then picked, counted, and identified.

Foraminiferal Isotope Analyses

All foraminifera, stained and unstained, used for isotopic analyses were stripped

of organic matter by soaking in 15% hydrogen peroxide for 20 minutes; this procedure

was followed by a methanol rinse. Live foraminifera had been sonicated following

identification, however, fossil (?) foraminifera had not been previously sonicated and

therefore to remove debris, fossil (?) foraminifera were sonicated in methanol (following

the removal of hydrogen peroxide). Due to differences in the strengths of the tests,

Epistominella pacifica, Bulimina mexicana, and Globobulimina pacifica were sonicated

for 3 minutes at 30% power, while Uvigerinaperegrina was sonicated at full power for 2

minutes. Following the methanol rinse, fossil (?) G. pacifica were broken to aid in

removing debris from within the test; they were then cleaned using water and a fine-

tipped paint brush. Fossil (?) G. pacifica was the only species analyzed where debris

could be seen within the test, perhaps due to the transparency of the test walls. All

samples were dried in the oven at 600 C.









The foraminifera were reacted at 730 C with anhydrous phosphoric acid in a Kiel

III device connected to a Finnigan MAT 252 isotope ratio mass spectrometer. The

purpose of the Kiel device is to limit the number of specimens required for accurate

analyses, which aids in determining the isotopic variation within individual species.

Foraminifera were analyzed for both 613C and 6180, whenever a sufficient number of

specimens were present to generate enough gas for the mass spectrometer. Typically,

enough gas was liberated when at least 20 |tg of foraminiferal tests were used, which

corresponded to between one and six tests per analysis, depending upon the species

analyzed. Whenever possible single tests were analyzed to better assess variability

within a species. With very large specimens of U. peregrina or G. pacifica, tests had to

be broken in half. Data is reported in the standard delta notation relative to the Pee Dee

Belemnite (PDB) standard. The precision, based on analyzing replicates of the NBS-19

standard, averaged 0.04 %o for 6180 and 0.08%o for 613C.

Pore-water DIC Analysis

Carbon Isotopes

Standards were prepared in order to determine both the accuracy and precision of

the pore-water DIC extraction technique. Two standards, with concentrations of 400

[tg/g KHCO3 and 750 [tg/g KHCO3, were prepared. The KHCO3 was analyzed as a solid

and yields a 613C value of-23.91%o. One standard was extracted for every five samples,

with the concentration of the standard used alternating between 400 [tg/g and 750 [tg/g

KHCO3. The 613C of the standards averaged -23.370.20 %o (lo). Sample data have

been corrected for the offset between the solid and dissolved standards.









Pore-water samples designated for carbon isotopic analyses (613C) were injected

and stored in pre-evacuated vacutainers. Five milliliters of standard solution (either 400

[tg/g or 750[tg/g KHCO3) was injected into pre-evacuated vacutainers. Prior to analysis,

the samples and standards were acidified with approximately 100 p.L of concentrated

H3P04 to reduce the pH. The carbon dioxide, which evolved from the acidified pore-

waters, was extracted from the vacutainers by puncturing the septum with a hypodermic

needle attached to a vacuum line (Martin et al., 1997). The gas, which is cryogenically

cleaned of contaminants, was stored in 5-mm glass tubes, which were flame-sealed. The

gas was then analyzed for 613C using an automatic cracker system attached to a VG

Prism II mass spectrometer.

Pore Water Solutes

Analyses of pore water solutes, excluding DIC, were performed on board of the

ship. Pore fluids were separated from the sediments using centrifugation. Chemical

analyses were performed for the following constituents: alkalinity, sulfate, sulfide,

calcium, magnesium, ammonium, phosphate, silicate, and nitrate. The chemical analyses

performed on board followed the methods used aboard the JOIDES Resolution (Gieskes

et al., 1991).

SEM Analysis

Selected specimens ofEpistominella pacifica and Uvigerinaperegrina were taken

from Monterey Bay and Eel River sites. The purpose of the SEM analysis was to

determine whether any recrystallization or overgrowths could be seen on the outside of

the tests. Samples were chosen from three general depths within the core (whenever










possible): near the sediment-water interface, the middle of the core, and the bottom of the

core (Table 2-4).

Foraminifera were mounted onto stubs using double-sided tape. Prior to SEM

analysis, the stubs were coated with a thin layer of a gold-palladium film, designed to

make the samples conduct electricity and minimize the buildup of charge on the surface

of the test. The foraminifera were analyzed using a JSM 6400 SEM at the Major

Analytical Instrumentation Center (MAIC) at the University of Florida. Two pictures of

each specimen were taken: an overall view of the test and a close-up of the test.

Table 2-4. Foraminifera used for SEM analysis.
SITE CORE SPECIES DEPTH STATUS
0.5
( Epistominella pacifica 16.5
S1780 HPC5 27.5 Fossil (?)
S15.5
Uvigerina peregrina 21.5
o 29.5
S1780 PC30 Uvigerina peregrina 0.5
Live
1780 PC67 Epistominella smith 0.5
Monterey 0.5
Bay-Clam 1780 HPC5 Uvigerina peregrina 15.5 Fossil (?)
Flats 24.5
Eel River-
Bubble Long Core 2 Epistominella pacifica
Site 10.5
1.5
: a 1 Fossil(?)
Epistominella pacifica 11.5
Long Core 4 18.5
12.5
W Uvigerina peregrina .5
17.5
0.5
l R r Epistominella pacifica .5
Eel River 12.5
- Bacterial Long Core 5 1.5 Fossil (?)
Mat Uvigerina peregrina 15.5
25.5
Eel River
Reference Long Core 1 Epistominella pacifica 4.5 Fossil (?)
Site___














CHAPTER 3
RESULTS



Pore Fluid Geochemistry

Monterey Bay

Pore water chemistry is distinctly different in the two clam beds sampled:

Invertebrate Cliffs (1780 PC 79) and Clam Flats (1781 PC 80) (Appendix A). For

instance, the calcium concentrations at Invertebrate Cliffs show virtually no change down

core, whereas the calcium concentrations at Clam Flats show variation with sediment

depth, decreasing more than 4 mM in the first 8 cm of the core (Figure 3-1). The Clam

Flats site also has significantly higher sulfide concentrations, with pore water values at

Clam Flats being up to 118 times higher than Invertebrate Cliffs (Figure 3-2). There are

also similar differences between the cores' alkalinity gradients. Changes in sulfide and

alkalinity likely correspond to sulfate reduction in the sediment (Figure 3-3).

The carbon isotopic compositions also differ between the dive sites. The 613CDIC

value from Clam Flats is approximately seven times lighter in the first centimeter of the

core than the 613CDIC of Invertebrate Cliffs. The DIC from Invertebrate Cliffs is found to

be no lighter than -9%o in the 12 cm of pore water analyzed, whereas Clam Flats 613CDIC

remains lighter than -40%o from 2 cm on to the bottom of the core (16 cm) (Figure 3-4).

Oxidation of marine organic carbon (613CDIC of -25%o) cannot account for the isotopically

light DIC found at Clam Flats. Although no bottom waters were collected from the











dives, supernatant fluid was extracted from the tops of cores designated for pore water


analyses and analyzed for 613CDIC(Table 3-1).


Ca (mM)


-- 1780 PC79
P1781 PC80


20
Figure 3-1. Pore water calcium profiles for Monterey Bay clam beds (Dive 1780 PC79,
Invertebrate Cliffs and Dive 1781 PC80, Clam Flats).


5- i ---------- ------------ ------------ ---------Yi_ 17 0 P 9

-- 1780 PC79
0





10 ----- 1781 PC80


15
C-








20
Figure 3-2. Pore water sulfide (HS-) profiles for Monterey Bay clam beds (Dive 1780
PC79, Invertebrate Cliffs and Dive 1781 PC80, Clam Flats).












Alkalinity (mM)


0 5


0


5





0
a 10





15





20


10 15 20 25 30 35 40


_-g- --- r ------ ---t p I -- ---- M e -B 1780 PC79
-- 1781 PC80


Figure 3-3. Pore water alkalinity profiles from Monterey Bay clam beds (Dive 1780
PC79, Invertebrate Cliffs and Dive 1781 PC80, Clam Flats).



613Cm, (%0 PDB)


-40 -30 -20


-10 0


- -






----* ----
*

------ ---------- ---------- ---------- -----


- E


Figure 3-4. The 613CDIC profile of pore water from Monterey Bay clam beds (Dive 1780
PC79, Invertebrate Cliffs and 1781 PC80, Clam Flats).


-50


u


5




. 10
10





15





20


* 1780 PC 79

* 1781 PC 80









Table 3-1. The 613CDIC values of supernatant fluids taken from the tops of cores
designated for pore water analyses.
Location Dive number Core Site Description 613CDIC value (%o)
M y Bay 1780 PC31 Yellow bacterial mat -3.72
Monterey Bay
1781 PC38 Reference (clam bed) -3.93
l R r B n 2052 PC8 Clam bed -5.72
Eel River Basin
2052 PC16 Bacterial mat -5.18

Eel River

The various sites sampled from Eel River: a bacterial mat, a clam bed, and a

bubble site, all exhibit similar pore water trends (Appendix A). For example, all of the

Eel River cores reveal an overall decrease in calcium concentration with depth, with

approximately similar gradients (Figure 3-5). All cores display similar bisulfide ion and

sulfate trends, although gradients differ; the bisulfide ion concentration increase more

rapidly with depth for PC19 (the bubble site) than for either PC8 (clams) or PC16, a

bacterial mat (Figure 3-6). The bubble site also has the steepest decreasing gradient for

sulfate, with complete consumption of sulfate by 10.5 cm (Figure 3-7). Additionally, all

cores have an increase in alkalinity with depth (Figure 3-8). The clam bed (PC8) and the

bacterial mat (PC16) have similar 613CDIc gradients, with both cores having core- top

supernatant fluid 613CDIC values of approximately -5%o (Figure 3-9, Table 3-1). The

bubble site (PC19) has initially lighter 613CDIC values, with a value of approximately

-18%o at 0.5 cm sediment depth. Within the top five centimeters of the core the 613CDIC

values begin to be lighter than that of oxidized marine organic carbon (- -22%o) (Figure

3-9).











Ca (mM)
0 2 4 6 8 10 12


0





5



-o
e
10
S15





15


20
Figure 3-5. Calcium pore water profiles for Eel River Dive 2052: PC16 (bacterial mat),
PC8 (clam bed), and PC19 (bubble site).



HS (mM)


-e- 2052 PC16

--- 2052 PC8

-'- 2052 PC19


20
Figure 3-6. Pore water sulfide profiles for Eel River Dive 2052: PC16 (bacterial mat),
PC 8 (clam bed) and PC19 (bubble site).


- -2052 PC16

I- 2052 PC8

S-2052 PC19


0





5



o

10






15












SO (mM)
4

0 5 10 15 20 25 30











S/ -- 2052 PC16


0--- 2052 PC19




1 5 - - - -





20

Figure 3-7. Sulfate ion pore water profiles from Eel River Dive 2052: PC16 (bacterial
mat), PC 8 (clam bed) and PC19 (bubble site).



Alkalinity (mM)
0 5 10 15 20 25 30 35 40


0





5

C
-o

10





15





20


- 2052 PC16

- 2052 PC8

- 2052 PC19


Figure 3-8. Pore water alkalinities for Eel River Dive 2052: PC8 (clam bed), PC16
(bacterial mat), and PC19 (bubble site).


... I... ....I.... I .. I


1111







30

613CDC, (%0 PDB)
-40 -35 -30 -25 -20 -15 -10 -5 0
0




5


S-e--- 2052 PC 16

S10 ------- ------ 2052 PC 8

-- 2052 PC 19

----+-- ---;-------:--------- ---- I---
15




20
Figure 3-9. Pore water 613CDIC for Eel River Dive 2052 PC16 (bacterial mat), PC8 (clam
bed) and PC19 (bubble site).


Stable Isotopic Signatures of Foraminiferal Carbonate

Monterey Bay

Carbon isotopes

The foraminifera from Invertebrate Cliffs display a range of 613C values (Table 3-

2, Appendix B). Sediments at the Invertebrate Cliffs clam bed (1780 PC30) contain live

U. peregrina with 613C values ranging from -0.04 to -0.85 %o, over the entire length of

the core, while the 613C of fossil (?) U. peregrina from HPC5 (Invertebrate Cliffs clam

bed) varies from 0.01 to -1.05 %o (Figure 3-10). Additionally, when the 613C values of

individual live U. peregrina from within the same depth interval are compared, variations

up to 0.55 %o are observed at 0.5 cm and 4.5 cm. A smaller range of 613C values is

evident in other species; for instance, live specimens of E. pacifica range from -0.50 to









-0.79 %o over the length of the core, PC30, whereas fossil (?) E. pacifica from HPC5

vary between -0.13 to -1.16 %o over the entire length of the core (Figure 3-11). Live B.

mexicana range between -0.70 and -0.92 %o within PC30 and fossil (?) specimens from

HPC5 vary between -0.52 and -1.04 %o (Figure 3-12). Most species of fossil (?)

foraminifera have a wider carbon isotopic range compared to their living counterparts.

G. pacifica is the only species sampled from Invertebrate Cliffs where live 613C values

have a broader range compared to fossil (?) 613C values (Figure 3-13). For most species

from Invertebrate Cliffs, however, the number of fossil (?) tests analyzed greatly

surpasses the number of live tests analyzed, possibly contributing to the greater variation

in the fossil (?) isotopic composition relative to the live composition (Table 3-2).

Table 3-2. A statistical comparison ofMonterey Bay foraminifera
Dive
No./ Mean + Min Max Mean + Min Max
Core Species Status n 613C (13C) (%o) (%0) 180 (6180) (%o) (%o)
No.
Live 9 -0.80 0.08 -0.92 -0.70 3.28 0.04 3.2 3.36
B. mexicana Fossil 1 -0.83 N/A N/A N/A 3.33 N/A N/A N/A
Fossil (?)* 17 -0.75 0.16 -1.04 -0.52 3.47 0.24 3.05 3.94
0 Live 12 -0.65 0.10 -0.79 -.50 3.18 0.07 3.09 3.30
E. pacifica
S .pac Fossil (?)* 70 -0.45 0.15 -1.16 -0.13 3.28 0.17 2.31 3.60
0 Live 27 -0.50 0.18 -0.85 -0.04 3.06 0.18 2.59 3.40
U. peregrina Fossil 2 -0.80 0.21 -0.95 -0.65 3.13 0.10 3.06 3.20
Fossil (?)* 33 -0.59 0.29 -1.05 0.01 3.25 0.13 3.06 3.73
Live 25 -1.38 0.48 -2.23 -0.41 3.32 0.07 3.23 3.49
G. pacifica
Fossil (?)* 24 -1.04 0.22 -1.69 -0.61 3.40 0.11 3.26 3.71
B. exicana Live 3 -1.09 0.07 -1.17 -1.03 3.44 0.31 3.22 3.80
Fossil 5 -1.43 0.48 -2.24 -1.04 4.74 0.09 4.65 4.89
Live 4 -0.96 0.04 -0.98 -0.92 4.25 0.73 3.15 4.66
SE.pacifica Fossil 4 -1.15 0.06 -1.20 -1.09 4.61 0.03 4.59 4.65
S p i Live 37 -0.91 0.45 -2.05 -0.10 3.20 0.16 3.04 4.04
^ U. peregrina
Fossil 15 -1.41 0.31 -2.03 -1.03 4.65 0.10 4.49 4.83
G. pacifica Live 3 -3.97 0.54 -4.56 -3.49 3.30 0.11 3.20 3.42
*Indicates foraminifera are from 1780 HPC5. **Statistical analyses were unavailable as
only one isotopic value was obtained for these specific foraminifera.








32



No systematic variations in the carbon isotopic patterns can be discerned for


Invertebrate Cliffs (Dive 1780 PC30). Isotopic values fluctuate randomly, but generally


remain around the same isotopic values throughout the length of the core.


13C (%o PDB)
-2.5 -2 -1.5 -1 -0.5 0 0.5



5
---------E------ E&"9




10 -
: 000 0

S15 -: : o PC30 U. peregrina (live)
SPC30 U. peregrina (fossil)
U 20 -ioo o HPC5 U. peregrina (fossil (?))


25 -


30


35
Figure 3-10. Dive 1780 HPC5 and PC30 (Invertebrate Cliffs clam bed) Uvigerina
peregrina 613C vs. depth.


613

-2.5 -2 -1.



5 -


10

-I



20 ---


25 "
30 ^ ----- --------


30


35 '

Figure 3-11. Dive 1780 HPC5
pacifica 613C vs. depth.


C (%o PDB)

5 -1 -0.5 0 0.5


n a
............ -----






-D -
in


------ ------ --
------------


El [T


- I I I .


o PC30 E. pacifica (live)
E HPC5 E. pacifica (fossil (?))


and PC30 (Invertebrate Cliffs clam bed) Epistominella












613C (%oPDB)


-1.5 -1 -0.5 0 0.5


0



5



10



15



20



25



30


I


Figure 3-12. Dive 1780 HPC5 and PC30 (Invertebrate Cliffs clam bed): Bulimina

mexicana 613C vs. depth.


613C (%oPDB)

-2.5 -2 -1.5 -1 -0.5 0 0.5


0




0 0
1 5 -----. --..... -.. .-... -..-............

-0 ------------- Q------- --------- -------r----- -









0: a
iEl


2 0 ------ ---- -------------- -

25



3 05 ------
30



35


1


O PC30 G. pacifica (live)

[ HPC5 G. pacifica (fossil (?))


Figure 3-13. Dive 1780 (Invertebrate Cliffs clam bed) HPC5 and PC30 Globobulimina

pacifica 613C vs. depth.


-2.5 -2


0








Koo
-- ---0-----



o



oo:

0
SoI





,i ..., i


e
r0


a
0

J


e


a
0,


0 PC30 B. mexicana (live)

1 PC30 B. mexicana (fossil)

0 HPC5 B. mexicana (fossil (?))









Variable carbon isotope values are also observed at the Clam Flats site (Dive

1781 PC31), with the 613C of live U. peregrina ranging from -0.10 to -2.05%o (Figure 3-

14); this large variation is observed between individuals within the same depth interval

(2-2.5 cm). The carbon isotopic range of fossil U. peregrina is smaller than the range

found for live specimens, with values lying between -1.03 and -2.03 %o. U. peregrina is

the most abundant species of foraminifera from Clam Flats; however, the 613C of other

foraminiferal species at the Clam Flats site used for comparison purposes with other

cores is presented (Figure 3-15). These other species, including the shallow infaunal

species E. pacifica and B. mexicana fall within the range of values found for U.

peregrina. Live E. pacifica varies between -0.92 and -0.98 %o, while fossil specimens of

E. pacifica range from -1.09 to -1.20 %o. Live B. mexicana vary from -1.03 to -1.17 %o,

while their fossil conspecifics vary between -1.04 and -2.24 %o over the length of the

core. The isotopic values of live G. pacifica, a deeper infaunal species, which vary

between -3.49 and -4.56 %o, is slightly lighter than values obtained from U. peregrina.

The last species presented, Planulina species, which is an epifaunal foraminiferan, has

carbon isotopic values ranging between -0.22 and +0.45 %o, which is slightly heavier

than most of U. peregrina's isotopic values.

From the data available, there is no systematic variation in carbon isotopes with

depth for PC31 (Clam Flats). No discernible disparities exist between live and fossil

conspecifics. When looking at the length of the core, fossil U. peregrina fall within the

isotopic range found for live U. peregrina (Figure 3-14). Both E. pacifica and B.

mexicana also have similar ranges for live and fossil conspecifics over the length of the

core (Figure 3-15).













13C (%o PDB)
-2.5 -2 -1.5 -1 -0.5 0


01


1




- 2
0



3




4




5


S00 0 o




a o o o'o o o



0 0 O 0 0.



O0 0 0 00




S--------- --------- ---------


Figure 3-14. Dive 1781 PC31 (Clam Flats clam bed) Uvigerinaperegrina 613C vs. depth


13C (%o PDB)
-5 -4 -3 -2 -1 0 1
0







xx
0 B. mexicana (fossil)
02
"2 -------.... ---- ------.----- .......---
2 o Lo B. mexicana (live)
S0 G. pacifica (live)
X+ x E. pacifica (fossil)
3 + E. pacifica (live)



4 ---- ---- I-- --- -- -- -- -- --
4

o OO


5

Figure 3-15. Dive 1781 PC31 Clam Flats (clam bed): Epistominellapacifica, Bulimina
mexicana, Globobulimina pacifica, and Planulina species 613C vs. depth.


0 U. peregrina (live)
O U. peregrina (fossil)


I









Oxygen isotopes

Oxygen isotopes also vary for a given species of benthic foraminifera; however,

similar to carbon isotopes, no down-core trends occur. E. pacifica and B. mexicana from

1780 PC30 (Invertebrate Cliffs) both have a slightly larger variation in fossil (?) 80O

than in live 6180 (Figure 3-16, 3-17). U. peregrina was the only species analyzed from

1780 PC30 that has greater 6180 variability for live specimens compared to fossil (?)

specimens (Figure 3-18). Live G. pacifica, which shows the largest variation in 613C (O

= 0.54 %o) has a relatively narrow range of 6180 values, varying up to 0.22 %o within

1780 PC30 (Figure 3-19). The oxygen isotopes do not vary appreciably from live to

fossil conspecifics found at the same depth within the core (Figures 3-16, 3-17, 3-18, and

3-19).

When live and fossil foraminifera from Clam Flats are compared to each other,

they have for the most part different 6180 signatures (Table 3-2, Figure 3-20). For the

entire core, the average 6180 value for fossil U. peregrina (n=15) is 4.65 0.10 %o.

Alternatively, the live U. peregrina (n=37) have a mean of 3.20 + 0.16 %o over the length

of PC31. Unlike these differences in 6180, the carbon isotopic values for live and fossil

U. peregrina show some overlap in value, even though mean 613C values are lighter for

fossil specimens (Table 3-2, Figure 3-15). Similar offsets are seen in other species from

Clam Flats (1781 PC31) (Table 3-2).

Eel River

Carbon isotopes

No live foraminiferal data are available from Eel River, however fossil (?)

foraminifera were analyzed for all Eel River sites (Appendix B). Long core 5, which













180 (%o PDB)

2 2.5 3 3.5


50 i
5 ---------



10



15
S:

20
20----------

25



30


:0



-- --- --- El---- ---------- ------- _


O
0
an
[El h
00
I a


m
na

Co
m
n
V1mT
[3 []
0[a


Figure 3-16.

pacifica 6180


Dive 1780 HPC

vs. depth.


5 and PC30


(Invertebrate Cliffs clam bed) Epistominella


180 (%o PDB)

2 2.5 3 3.5


Figure 3-17. Dive 1780 HPC5

mexicana 6180 vs. depth.


4 4.5


O PC30 B. mexicana (live)

L1 PC30 B. mexicana (fossil)

0 HPC5 B. mexicana (fossil (?))


and PC30 (Invertebrate Cliffs clam bed) Bulimina


4 4.5


0 PC30 E. pacifica (live)

D HPC5 E. pacifica (fossil (?))


0


o



------------ -------.. -- ----- -------





00
00
0 0
--- --- --- -- --- -----------^



- ----------------.------------------ .-------..
i i i i i i i i i i i i i0












180 (%o PDB)

2.5 3 3.5


0 '' "O








o o
5 00
10 ~ ~ ~ 0 0-------- :------------ --------




20 00


25 o0

25 ------------ -0---- -----
0
---------------------- ------ ------^---- --------

30

I I , ,


O PC30 U. peregrina (live)

l PC30 U. peregrina (fossil)

0 HPC5 U. peregrina (fossil (?))


Figure 3-18. Dive 1780 (Invertebrate Cliffs clam bed) HPC5 and PC30: Uvigerina
peregrina 6180 vs. depth.


180 (%o PDB)
2 2.5 3 3.5 4 4.5


O PC30 G. pacifica (live)

1 HPC5 G. pacifica (fossil (?))


Figure 3-19. Dive 1780 (Invertebrate Cliffs clam bed) HPC5 and PC30 Globobulimina

pacifica 6180 vs. depth.


4 4.5


0


5



10



15



o 20
20



25



30



35


J


0

[M]




--------------------------




m:

^o I


I l l l l l l l l' ''










180 (%o PDB)
3 3.5 4 4.5 5 5.5
0 1 I1

o p


O 1DD n O


-2 ----------- ---.- --- ----
D m O U. peregrina (live)
S- U. peregrina (fossil)



5 (D 0[

4
4 .---- -------- --- --- : -------- -------.




5
Figure 3-20. Dive 1781 PC31 (Clam Flats clam bed) Uvigerinaperegrina 6180 vs.
depth.


was collected from a bacterial mat, contains fossil (?) U. peregrina that have a mean

613C value of -1.49 2.10 %o (Table 3-3, Figure 3-21). If, however, three of the outlying

values are excluded, specifically 4.48, -6.97 and -11.59%o, the mean 613C value

increases to -0.93 0.28%o. Fossil (?) E. pacifica isotope values range from -1.01 to

-0.32 %o (Figure 3-21). The other two cores, Long core 4 and Long core 2 contain

foraminifera with extreme ranges in 613C values. For instance, Long core 4, which was

taken in a clam bed, contains U. peregrina specimens with 613C values ranging from

-0.46 to -7.13%o (Figure 3-22). Even more extreme, the 613C ofE. pacifica ranges from

-0.65 to -19.46 %o, with the lightest of values occurring rather shallowly at 1.5 cm.

However, the majority of the foraminifera from Long core 4 have a 613C value of









approximately 2%o or heavier (Figure 3-22). In contrast, Long core 2 (from the bubble

site) has more variable 613C values than LC4 (Figure 3-23). For example, out of a sample

set that includes 33 U. peregrina data points, the range in 613C values is from -0.65 to

-23.22%o (Figure 3-23), with a mean 613C of -6.70%o, and a standard deviation (c) of

7.00%o (Table 3-3). B. mexicana and E. pacifica show similar variability. The variation

in 613C for all cores is unsystematic with depth.

Table 3-3. A statistical comparison of fossil (?) foraminifera from Eel River Basin.
Dive
Number Mean o Min Max Mean a Min Max
and Core Species n 13C (813C) (%o) (%o) 8180 (6180) (%o) (%o)
Number
U. peregrina 33 -6.70 7.00 -23.22 -0.65 3.60 0.61 2.14 4.76
2052 Long
Core2 E. pacifica 18 -3.46 4.99 -15.24 -0.16 3.36 0.46 2.76 4.03
B. mexicana 15 -12.73 6.12 -21.13-0.71 4.05 0.19 3.83 4.51
2052 Long U. peregrina 32 -1.37 1.55 -7.13 -0.46 3.56 0.34 2.81 4.05
Core4 E. pacifica 20 -2.94 4.52 -19.46 -0.65 3.70 0.28 3.08 4.30

2052 Long U. peregrina 36 -1.49 2.10 -11.59 -0.41 3.70 0.17 2.99 3.97
Core 5
ore E. pacifica 17 -0.75 0.20 -1.01 -0.32 3.67 0.14 3.37 3.97


Oxygen isotopes

Variable 6180 values accompany the wide range of 613C values for Eel River

cores. The bubble site (LC2), which has the most variable 613C values, also has the

widest range of 6180 values, ranging from 2.14 to 4.76%o throughout the core (Figure 3-

24, Table 3-3). The majority of foraminiferal 6180 values from long core 4 (clams) are

between 3 and 4%o (Figure 3-25); likewise, the majority of foraminifera from long core 5

(bacterial mat) have 6180 values between 3.5 and 3.9%o (Figure 3-26). No down core

trends in variability could be distinguished for any of the Eel River cores.













13C (%o PDB)

-10 -8 -6 -4


-2 0


Figure 3-21. Dive 2052 long core 5 (bacterial
Epistominellapacifica 613C vs. depth.


o U. peregrina (fossil (?))

E E. pacifica (fossil (?))


mat): Uvigerinaperegrina and


13C (%o PDB)

-15 -10 -5 0


D





. .


0
EZ)

10

UD


o 1D
a o






00 O0
CE
m

a
a

DO


o E. pacifica (fossil (?))

a U. peregrina (fossil (?))


Figure 3-22. Dive 2052 Long core 4 (clam

peregrina 613C vs. depth.


bed): Epistominellapacifica and Uvigerina


0 : 0 El






0 D
o




------ ---- --- --- ----- -- ------- -

o



m)

o

- -.. ---. ------ ----. ---- -------- --- --- _
oo
0 V
OD
- - - - -L -
p 0














-25
0





5





10





15


-20


13C (%o PDB)

-15 -10 -5


0



0
0 O



O 0
0 C

S0 0

0




0o

SI


aCm






0
o


Figure 3-23. Dive 2052 Long core 2 (bubble site):
pacifica, and Bulimina mexicana 613C vs. depth.



180 (%o PDB)
2 2.5 3 3.5 4 4.5 5
0 ....' :' o. '' ....
0






00 0
o o


100 0 o C
10 .......o : o o <>


'o


I I I
1 5 - -o-- -. -. - -- .. .

S :5O
gD


o U. peregrina (fossil (?))
E E. pacifica (fossil (?))

0 B. mexicana (fossil (?))


Uvigerina peregrina, Epistominella


o U. peregrina (fossil (?))
a E. pacifica (fossil(?))
o B. mexicana (fossil (?))


Figure 3-24. Dive 2052 long core 2 (bubble site): Uvigerinaperegrina, Bulimina
mexicana and Epistominellapacifica 6180 vs. depth.













180 (%o PDB)


2 2.5 3 3.5 4 4.5 5


S r o


Eo 0 U










0 UO
SCO





IE0
QDn


o o

o
Lu


o E. pacifica (fossil (?))
L U. peregrina (fossil (?))


Figure 3-25. Dive 2052 long core 4 (clam bed): Epistominellapacifica and Uvigerina

peregrina 6180 vs. depth.


180 (%o PDB)


3 3.5 4
S' Id '!
S d o
o0:


o:




0
0
o
----------- --
o
EU




ao
..- .-------- o--
0D
Do
,--I-....--i---.---


4.5 5


o U. peregrina (fossil (?))

E E. pacifica (fossil (?))


Figure 3-26. Dive 2052 Long Core 5 (bacterial mat): Uvigerinaperegrina and
Epistominellapacifica 6180 vs. depth.


0





5


C
-I

10

aC



15





20


2 2.5
0



5 -----




10 --



15 --



20



25 ------


I









Scanning Electron Microscope (SEM) Micrographs

No evidence of recrystallization or overgrowths is visible from the micrographs

taken from Monterey Bay's Invertebrate Cliffs or Clam Flats (Appendix C, Figure 3-28

and Figure 3-29). This observation was consistent with the isotopic composition of the

foraminifera, which did not have unusually light carbon signatures.

Some of the foraminifera photographed from Eel River appear to be

diagenetically altered (Appendix C, Figure 3-30). The photographed specimens are from

2052 long core 4, the clam bed, however, it is likely other Eel River cores also contain

recrystallized foraminifera or foraminifera containing authigenic carbonate, based on the

light carbon isotopic signatures present in some foraminifera.



















(a)






















(b)









Figure 3-27 (a, b). A scanning electron micrograph of an Uvigerinaperegrina from
Monterey Bay's Invertebrate Cliffs clam bed. This specimen was taken from 21-22 cm
and was not cleaned before analysis. (a) An overall shot of the test. (b) A close up of the
test from the region identified in (a).

















(a).
























(b).












Figure 3-28. A scanning electron micrograph of an Epistominellapacifica from
Monterey Bay's Invertebrate Cliffs clam bed. Specimen was taken from 27-28 cm depth.
Specimen was cleaned before analysis. (a). An overall view of the test. (b). A close-up
of the test from the region identified in (a).



















(a)

































Figure 3-29 (a,b). A scanning electron micrograph of a U. peregrina from Eel River's
long core 4 (clam bed). Specimen was taken from 8-9 cm depth and was cleaned prior to
analysis. (a) An overall view of the test. (b). A close-up of the region identified in (a).














CHAPTER 4
DISCUSSION



Although cold seep locations and foraminiferal distributions are well documented,

previous research reporting the isotopic compositions of seep foraminifera is scarce.

Previous studies have shown that seep-inhabiting foraminifera have no special

adaptations that enable them to inhabit seep sites (Bernhard et al., 2001), where sulfide

and methane concentrations can reach potentially toxic levels. Some seep inhabiting

species, however, do appear to have variable carbon isotopic values (Sen Gupta et al.,

1997; Rathburn et al., 2000); pore water was not collected during either of these prior

studies (Sen Gupta et al., 1997; Rathburn et al., 2000), so the relationship between pore

water 613CDIc and the 613C of foraminiferal carbonate was not analyzed.

The Effects of Methane on Pore Water Composition

The DIC in pore waters is a mixture of three end-members: seawater DIC, which

has a 613C approximating 0%o PDB, oxidized organic matter (613C = -25%o), and oxidized

methane, which has 613C values typically between -25 and -50%o (Whiticar, 1999). The

relative amounts of marine organic matter oxidation and seawater present in the

subsurface will influence the pore water composition; if enough seawater is present

within the sediments, it could increase the 613CDIC enough to conceal an isotopically light

methane signature. Pore water composition is altered by the activity of clams, which

intensify the downward mixing of relatively heavy seawater and pore water, leading to a









heavier 613CDIC signature. For example, in dense Calyptogena clam beds, the flux of

seawater resulting from bioirrigation caused by bivalves was found to exceed the upward

advection of pore fluids by several orders of magnitude at Aleutian cold seeps (Wallman

et al., 1997).

Bacterial activity occurring within the sediment will also alter pore water

composition. For instance, the microbial breakdown of organic matter, by a reaction

similar to:

2CH20 + S042 -, HCO3- + H2S, (2)

will result in increased alkalinity and increased sulfide concentrations within pore waters.

Bicarbonate produced from the microbial reduction of organic matter would yield 613C

values of approximately -25 %o. In addition to the above reaction, anaerobic methane

oxidation often occurs at cold seep environments and also leads to increases in alkalinity.

Anaerobic methane oxidation consumes sulfate and methane by the net reaction:

CH4 + S042- HCO3- + HS- + H20 (3)

(Reeburgh, 1976). Since bicarbonate is a product, and the dominant component of the

DIC at a neutral pH, the 613CDIC should record the isotopically light carbon signature

inherited from the methane.

The Invertebrate Cliffs clam bed (1780 PC30) shows little indication of the

occurrence of methane oxidation, based on 613CDIc, alkalinity, and bisulfide ion profiles.

Pore water 613CDIC values are heavier than -8.6%o in the upper 12 cm of the sediment

column, and sulfide and alkalinity profiles show virtually no changes over the length of

the core, with values remaining around 1 mM and 3 mM, respectively. Alternatively,

pore waters at Clam Flats show light 613CDIC values, high alkalinity and downcore









increases in sulfide. The presence of613C values less than -25%o confirms the presence

of methane and its subsequent oxidation in the pore water.

The differences in the pore water compositions at Invertebrate Cliffs and Clam

Flats could have a variety of causes. For instance, the Invertebrate Cliffs clam bed may

have lower seepage rates or if seepage is episodic, it is possible that seepage had occurred

more recently at Clam Flats, leading to isotopically lighter DIC and increased alkalinity

and sulfide concentrations compared to Invertebrate Cliffs. Additionally, higher rates of

bioirrigation could mask the isotopically light seep signature of Invertebrate Cliffs.

Furthermore, a different methane source (possibly more thermogenic methane, which is

isotopically heavier than biogenic methane), could account for some of the disparity

between the two sites. Most likely, however, it is a combination of these processes that

may have masked the isotopically light methane signature of the Invertebrate Cliffs seep.

Like the Clam Flats clam bed, all of the Eel River cores show a down core

increase in alkalinity coupled with an increase in sulfide. The mixing of bicarbonate

from marine organic carbon and the bicarbonate in seawater cannot account for the light

613C displayed by the pore water from the Eel River cores, which decrease below -25%o

(Figure 3-9). Methane oxidation must be occurring in the subsurface. In addition, the

microbial activity responsible for methane and organic matter oxidation, which increase

alkalinity, could initiate the precipitation of authigenic carbonate; this could explain the

decreasing calcium concentrations with sediment depth.

Pore Water, Methane, and the Isotopic Composition of Foraminiferal Tests

The carbon isotopic composition of foraminifera differs from that which would be

produced by direct precipitation from solution due to the processes of biogenic carbonate









formation. These differences between abiotic carbonate formation and biogenic

carbonate formation are generally characterized as "vital effects". According to

Grossman (1987), the source for most foraminiferal carbonate is inorganic carbon-

oxygen compounds; however, isotopically light carbon-oxygen compounds resulting

from both metabolic activities within the organism, as well as organic matter, may also

contribute to calcification of the test (Grossman, 1987). Foraminifera inhabiting seep

sites would, at least periodically, be inhabiting isotopically light pore waters, depending

on the relative contributions of methane oxidation, sea water DIC, and marine organic

matter.

The heterogeneous nature of methane release along with variations in the timing

of test calcification could create intraspecific isotopic variations in foraminiferal

carbonate. For instance, the Green Canyon area in the Gulf of Mexico displays a wide

range of conspecific foraminiferal 613C values compared to non-seep areas. However,

Rose Bengal stained foraminifera at this site are sparse (i.e., most individuals were dead

at the time of collection), therefore only unstained tests were analyzed. These tests may

have been influenced by diagenetic processes. Sen Gupta and Aharon (1994) report

variations up to 1.9 %o in the carbon isotopic composition of unstained U. peregrina from

the upper centimeter of a core at a Gulf of Mexico hydrocarbon seep.

Diagenesis as a Contributing Factor to Isotopically Light Foraminiferal Carbonate

Although methane appears to create variability in the carbon isotopic composition

of foraminifera, it does not appear to explain the negative isotopic excursions seen in

some fossil foraminifera. Other factors, such as diagenesis, may have influenced the

isotopic composition of these foraminifera. Depending upon the composition (and the









saturation state) of the pore fluids, fossil foraminifera could either be recrystallized or

become sites of authigenic carbonate precipitation. This would not only create variability

in fossil foraminiferal tests, but would also create more negative carbon isotopic

compositions, since these carbonates would be in isotopic equilibrium with pore fluids,

unlike the foraminiferal carbonate precipitated during the life of the foraminifera.

Instead of hydrate destabilization, which was the theory proposed by Kennett et al

(2000) to explain variations in foraminiferal test carbonate during the Pleistocene, Stott et

al. (2002) proposed that in the modern Santa Barbara Basin, changes in the flux and

oxidation of organic carbon associated with variations in productivity and habitat depth

generate variation in the isotopic composition of live benthic foraminifera.

The 613C of pore waters sampled were isotopically heavier than -18 %o in the

upper 4.2 meters of sediment at the Santa Barbara basin center and slightly heavier at the

basin slope (Stott et al., 2002). These pore water values show little evidence of an

influence by methane, which today enters the basin through cold seep environments

(Stott et al., 2002). Foraminifera inhabiting these pore waters, specifically Buliminella

tenuata, an infaunal foraminifera, had carbon isotopic values that approximated pore

water 613CDIC values at 3 to 4 mm, which is where they are believed to calcify their tests

(Stott et al., 2002); carbon isotopic values for B. tenuata were around -3 %o (Stott et al.,

2002).

Stott et al. (2000) reported that increases in the rates of carbon oxidation led to a

-1.5 %o shift in the average 613C of B. tenuata between the early 1900s and the 1960s.

Because today these foraminifera seem to accurately record pore water 613CDIc, Stott et

al. (2002) suggested that as productivity in the North Pacific varied due to climatic









changes during the Pleistocene, so did the pore water 613C and the foraminiferal

carbonate values. This theory may be applicable to non-seep sites in the modern Santa

Barbara Basin; however, no seep sites were sampled to determine the isotopic variability

of Santa Barbara seep foraminifera.

Diagenesis was also listed as a possible contributing factor to the negative carbon

isotopic compositions of Pleistocene foraminifera from the Santa Barbara basin, which

Kennett et al. (2000) found to vary up to 5%o between stadials and interstadials. Reimers

et al. (1996) found that the pore waters become supersaturated with respect to calcite

below 2 cm, which could affect the down core carbonate record through secondary calcite

precipitation.

For this study, although foraminiferal tests were microscopically examined for

evidence of diagenesis before analysis, authigenic carbonate grains could have been

present within the chambers of some of the tests. Many diagenetic processes may

influence fossil tests. For instance, the bacterial decomposition of biological tissue, such

as the protoplasm of foraminifera, under anoxic conditions generates ammonia and

carbon dioxide, which lead to increased alkalinity (Berner, 1980). Additionally, if the

bacterial reduction of sulfate is occurring within the sediment, alkalinity will increase

further. As a consequence of these reactions, the degree of saturation with respect to

carbonate minerals does increase. Depending on the degree of saturation, specifically

whether supersaturation is reached, authigenic carbonate may be precipitated. This initial

carbonate precipitation may function as a nucleus for continued growth, assuming that

supersaturation is maintained (Berner, 1980).









The bacterial decomposition of the protoplasm, however, is probably more

important for the formation of authigenic iron minerals, such as pyrite, because of the

production of sulfide resulting from the reduction of sulfate, than for authigenic

carbonate formation (Berner, 1980). Iron is probably readily available in the reducing

pore waters and siliciclastic sediments of the seeps. Some of the authigenic carbonates

from Monterey Bay analyzed by Stakes et al. (1999) contained fossil foraminifera whose

chambers were concentrically filled with pyrite framboids encased in high-Mg calcite.

However, pyrite formation is not solely associated with diagenetic processes, as it may

also form in the tests of live foraminifera due to anaerobic bacterial activity occurring

within the organism (Seigle, 1973).

Diagenesis in the Eel River Basin

Methane seepage alone cannot account for all of the isotopic variability seen in

Eel River basin foraminifera. The fossil (?) foraminifera from Eel River sites had carbon

isotopic compositions up to 21.3%o lighter than Monterey Bay foraminifera and oxygen

compositions, which were heavier than Monterey Bay by up to 0.72%o; this excludes the

fossil foraminifera from Clam Flats, which had, in general, heavier oxygen isotopes than

Eel River foraminifera (Table 4-1).

Table 4-1. A comparison of the mean 613C and 6180 values of U. peregrina from
Invertebrate Cliffs (1780 PC30), Clam Flats (1781 PC31), and Eel River (2052 LC2,
LC4, and LC5).
Site
Dive and Core No. sitie Mean 83C a (813C) Mean 8O6 0 (6 80)
Description
1780 PC30 (fossil ?) Clam bed -0.59 0.29 3.25 0.13
1781 PC31 (fossil) Clam bed -1.41 0.31 4.65 0.10
2052 LC 2 (fossil ?) Bubble site -6.70 7.00 3.60 0.61
2052 LC 4 (fossil ?) Clam bed -1.37 1.55 3.56 0.34
2052 LC 5 (fossil ?) Bacterial mat -1.30 1.91 3.70 0.17









Using the geochemical modeling program PHREEQC (Parkhurst and Appelo,

1999), saturation indices were calculated for the Eel River cores; due to the lack of

necessary parameters (such as pH, magnesium, or sulfate), saturation states could not be

calculated for Monterey Bay. PHREEQC is a computer program that is designed to

perform a wide variety of low-temperature aqueous geochemical calculations including

speciation and saturation-index calculations (Parkhurst and Appelo, 1999). There are,

however, a couple of problems encountered when using PHREEQC for seawater

calculations. First, PHREEQC uses an ionic-strength term in the Debye Hiickel

expressions in an attempt to extend the limit of applicability of this model for seawater

ionic strengths (- 0.7 molal); the applicability of the model may fail if ionic strengths are

high (> -1.0 molal) (Parkhurst and Appelo, 1999). Another problem encountered with

the calculations is the inability to introduce pressure as a variable in the modeling, which

could have an effect on mineral formation at water depths of 500 to 1000 meters.

The bubble site (PC 19) was characterized by the most positive saturation indices

compared with the other Eel River sites, with dolomite more oversaturated compared to

calcite or aragonite (Figure 4-1). Long core 2, which contains foraminifera from the

bubble site, also had the most variable foraminiferal carbon values, with 613C values

ranging from -23.22 to -0.49%o. The saturation indices calculated for long core 4 (clam

bed) were also all positive, with dolomite being the most oversaturated, with saturation

indices up to 2.42, followed by calcite, then aragonite (Figure 4-2). The first sample of

long core 5 (bacterial mat), 0.5 cm, was undersaturated with respect to calcite and

aragonite. However, all depths below 0.5 cm were oversaturated with respect to

dolomite, calcite, and aragonite (Figure 4-3).







56



Saturation Index (SI)

0 0.5 1 1.5 2 2.5 3 3.5


--- Aragonite

--- Calcite

-0 Dolomite


Figure 4-1. A plot of the saturation indices (SI) versus depth for the bubble site (PC19,
which corresponds to the foraminifera from long core 2).


Saturation Index (SI)

0 0.5 1 1.5 2 2.5


I .. Aragonite
S-I--- Calcite
-- Dolomite
4 -


5 - i; ---- ----


6
6 ------ : ........ ... .... ---




Figure 4-2. A plot of the saturation indices (SI) versus depth for PC8 (clam bed, which
corresponds to the foraminifera from long core 4).


----




I -


- -- -- ---



(A I I h i -











Saturation Index (SI)

-0.5 0 0.5 1 1.5 2 2.5 3




5- --
5


o --E --- Aragonite
P 10 Calcite
S/ Dolomite


15 -- ------- ----. .




20
Figure 4-3. A plot of the saturation indices (SI) versus depth for PC16 (bacterial mat,
which corresponds to the foraminifera from long core 5).


Based on the values and the ranges of isotopes (carbon and oxygen) seen in fossil

(?) foraminifera from Eel River and the model-predicted saturation indices, it is likely

that secondary calcite precipitation is masking variability created by methane seepage. If

venting is episodic, during times of cessation of seepage the saturation of pore fluids is

likely to change from that of supersaturated to saturated (and possibly undersaturated),

which would cause authigenic carbonate precipitation to either cease or in the case of

undersaturation, could cause dissolution to occur. However, when seepage does begin,

the composition of pore fluids will once again be altered based on the relative amounts of

DIC contributed by seawater, organic matter oxidation, and methane oxidation. If

supersaturation occurs, precipitation will preferentially occur on foraminifera, which had

prior mineral growth, leading to increased variation in isotopic composition. In this way

variations as large as those seen in Long core 2, where at the most extreme 613C values









reach -23.22 %o at 9.5 cm depth and just a centimeter below this a U. peregrina has a

613C signature of-1.05 %o, can be generated.

Although saturation states were not calculated for Monterey Bay, based upon the

isotopic composition of the foraminifera, it is unlikely that diagenesis is affecting the

fossil foraminifera. In addition to no foraminifera having extremely light isotopes, such

as those seen in Eel River, the standard deviations for both carbon and oxygen isotopes

are relatively small (Table 3-2), with maximum standard deviations (C) of 0.48 and 0.29,

for 613C and 6180, respectively. If diagenesis were occurring, standard deviations should

be larger, due to variations in pore fluid composition and the possibility of multiple

periods of precipitation. Considering that live foraminifera from Monterey Bay, which

would not be affected by diagenetic processes, have larger standard deviations, (a

maximum of 0.55 for 613C and 0.73 for 6180), it further negates the presence of

diagenesis at these sites.

Stable Isotopic Compositions

The Variation in Foraminiferal Carbon Isotopes

Data focusing on the conspecific variation in foraminiferal carbonate isotopes are

limited, particularly within active seep environments. Within non-seep environments, the

carbon isotopic composition of most species of foraminifera varies little downcore,

despite changes in the isotopic composition of pore water (McCorkle et al., 1997). Live

U. peregrina from two non-seep sites, the North Carolina margin and the California

margin (south of Pt. Sur), were analyzed and found to have 613C variations less than

0.5%o over the length of a core (McCorkle et al., 1997). Accompanying pore water

613CDIC values for these cores, which were 14.5 cm or shorter, ranged from 1.10 to









-3.43%o (McCorkle et al., 1997). A slightly larger variation was seen in G. pacifica,

which is characterized as a deeper infaunal species, compared to U. peregrina; Live G.

pacifica displayed 613C variations up to 0.98%o in pore waters with 613CDIC ranging

between -0.32 and -2.54%o (McCorkle et al., 1997). However, live G. pacifica from the

California borderlands, a low-oxygen environment, showed less variation in 613C

downcore, with an intraspecies variation of 0.28%o (Mackensen and Douglas, 1989).

Fossil G. pacifica from the California borderlands showed slightly more variability in

613C than live specimens, with variations up to 0.33%o over 8-cm (Mackensen and

Douglas, 1989). No accompanying pore water data was available.

The lack of intraspecific variation at non-seep sites has been attributed to growth

within a narrow depth range, growth within microenvironments characterized by

relatively constant 613C values and food preferences (McCorkle et al., 1990; 1997;

Rathburn et al., 1996). Most individuals within a core would have a similar test

composition if growth took place within a specific microenvironment during short-lived

episodes, such as during an increase in food availability (McCorkle et al., 1997).

At Clam Flats, foraminifera found living at the same depth had isotopic

compositions that differed by as much as 1.95%o. These differences imply either that

calcification occurred during significantly different pore water conditions for the

foraminifera for at least a portion of their tests, perhaps in different microenvironments,

or that variations in the amounts of metabolic carbon dioxide incorporated into the test

may be causing variation in test 613C values. These two factors could be linked; a larger

amount of bacteria would be sustained during times of increased methane seepage,

leading to isotopically lighter pore water DIC. In addition, deposit-feeding foraminifera,









such as U. peregrina and G. pacifica, are known to ingest a large amount of sediment, as

well as algal cells, bacteria, and organic detritus (Goldstein, 1999). Bacteria in particular

seem to comprise an important role in the diet of deposit- feeding foraminifera (Goldstein

and Corliss, 1994). Growth should be encouraged during these times of increased food

availability, leading to variations in test composition not only by the occasional ingestion

of bacteria, which oxidize isotopically light methane, but also by the incorporation of

isotopically light DIC from the pore waters. This would, however, likely decrease

isotopic variability because all foraminifera would end up with light isotopic

compositions if the majority of growth occurred under these conditions.

Variations in foraminiferal carbonate among different species could be

enhanced by methane seepage due to increased variations in pore water 613C with depth.

The interspecific variation in the isotopic composition of foraminifera is much larger than

the intraspecific variation. Fractionation linked to growth rate may account for some of

the interspecies variation (McCorkle et al., 1997), with sporadic growth occurring during

times of increased bacterial activity related to methane release. However, differences in

the isotopic composition between species of foraminifera have verified that microhabitat

(environmental) effects influence the carbon isotopic composition of benthic foraminifera

(McCorkle et al., 1990; 1997). Variations in 613C values up to 3 or 4%o have been

documented between species of benthic foraminifera living within the same core

simultaneously (McCorkle et al., 1990; 1997; Rathburn et al., 1996). These disparities

were enhanced at seep sites, where deeper infaunal taxa were subjected to more depleted

pore waters compared to shallow infaunal and epifaunal species.









The difference in the 613C composition between epifaunal and deep infaunal

species of foraminifera from south of Pt. Sur varies up to 1.68%o (McCorkle et al., 1997).

The epifaunal species, Cibicidoides wuellerstorfi had 613C values ranging from -0.01 to

-0.20%o, compared to shallow infaunal Uvigerina species, which ranged from -0.49 to

-0.97%o, and the deep infaunal species, G. pacifica, which had 613C values between

-1.34 and -1.67%o (McCorkle et al., 1997). Epifaunal species at Clam Flats, such as

Planulina, have 613C values ranging from -0.22 to +0.45%o, compared to the shallow

infaunal species, U. peregrina, which ranges from -0.10 to -2.05%o, and G. pacifica, a

deep infaunal species, which has 613C values ranging from -3.49 to -4.56%o. The

maximum variation seen between infaunal and epifaunal species at Clam Flats was

5.01%o, compared to 1.68%o for the non-seep site south ofPt. Sur. This increased

variation is likely a result of the isotopically light 613CDIC found at seep sites, which

influences the infaunal foraminifera to a larger extent.

The Relationship between Methane, Pore Water 513C, and Foraminiferal Carbonate

The oxidation of methane produces bicarbonate that retains methane's

isotopically light carbon signature. Foraminifera, which primarily use inorganic oxygen-

carbon compounds (Grossman, 1987) to calcify their tests, could incorporate this

bicarbonate into their tests preserving the source's signature. However, when comparing

two Monterey Bay seep sites, the Clam Flats site and the Invertebrate Cliffs site, isotopic

differences are not as large as expected based on the differences in the values of pore

water 613CDIc at these sites. Pore waters at Clam Flats were characterized by isotopically

lighter DIC than at Invertebrate Cliffs (Figure 3-4). Live U. peregrina from Invertebrate

Cliffs range in 613C values from -0.04 to -0.85%o. Live U. peregrina from Clam Flats,









where 613C DIC values were four to six times lighter than at Invertebrate Cliffs, range

from -0.1 to -2.05%o, only approximately 2 times lighter than Invertebrate Cliffs. Other

species of foraminifera, specifically live E. pacifica and live B. mexicana, inhabiting both

sites had mean 613C values that were more depleted (by -0.30%o) at Clam Flats relative to

Invertebrate Cliffs. In all cases, although foraminifera from the site with the isotopically

lighter DIC had isotopically lighter tests (Table 4-2), the isotopic differences were not the

magnitude expected based upon prior fossil benthic foraminiferal analyses. Even though

the foraminifera appear to respond to and incorporate a portion of the isotopically light

DIC into their tests, a more significant portion of foraminiferal carbonate must come

from other carbon-bearing compounds.

Table 4-2. A comparison of the mean 613C values and standard deviations of live
foraminifera from Clam Flats (PC31) and Invertebrate Cliffs (PC30).
Invertebrate Cliffs 1780 Clam Flats
Species PC30 1781 PC31
Mean 613C T Mean 813C _C
U. peregrina -0.50 0.18 -0.91 0.45
E. pacifica -0.68 0.10 -0.98 0.04
B. mexicana -0.80 0.08 -1.09 0.07
G. pacifica -1.39 0.49 -3.97 0.55


It would be expected that deep infaunal species, such as G. pacifica, would be

influenced by more isotopically depleted pore waters compared to shallow infaunal taxa,

such as U. peregrina. As is the case in non-seep sites (McCorkle et al., 1990; 1997), this

expectation appears to be true for seep sites as well; the 613C of G. pacifica from both

sites is isotopically lighter than U. peregrina. The isotopic values of live G. pacifica at

Invertebrate Cliffs had average 613C values of -1.11 %o and -1.40%o compared to live G.









pacifica from the same depths (2.25 cm and 4.5 cm) at Clam Flats, which had 613C values

of -3.49%o and -4.56%o.

A Comparison of the Isotopic Composition of Seep and Non-seep Foraminifera

A comparison of foraminifera from known seep sites, with very different pore

water chemistries did not create the carbon isotopic differences expected based on prior

fossil foraminifera research. However, much of this early research (Wefer et al., 1994;

Dickens et al., 1995; Kennett et al., 2000) was looking at older fossil foraminifera, i.e.,

some from the Pleistocene, where it is unsure what type of environment was present

when these foraminifera were alive. The sites sampled for this study, however, are from

true seep sites, where evidence of seepage, such as bubbling, authigenic carbonate crusts

and chimneys, and cold seep communities, such as clams and bacterial mats, are present.

Nonetheless, the seep sites have different isotopic compositions compared to non-

seep sites. For instance, from cores in the Atlantic and the Pacific Oceans, McCorkle et

al. (1990) collected data confirming a shallow infaunal habitat for U. peregrina.

Additionally, the 613C of U. peregrina was found to be nearly equal to the 613CDIC from

the top few millimeters of the cores, values typically between -0.6 and -1.2%o (McCorkle

et al., 1990). At Clam Flats live U. peregrina have 613C values no lighter than -2.05%o

although the 613CDIC of pore water at 0.5 cm sediment depth was -36%o. In addition, even

Invertebrate Cliffs, which at present shows little sign of methane seepage, has a pore

water 613CDIC value of -4.78%o at 0.5 cm sediment depth compared to live U. peregrina

isotope values no lighter than -0.85%o.

McCorkle et al. (1990; 1997) and Rathburn et al. (1996) determined that in order

to compare living foraminifera from different regions, the 613C DIC of bottom water (b.w.)









must be subtracted from the foraminiferal 613C value, yielding a value termed A813C.

Actual bottom water samples were not collected during dives for this study; however, the

supernatant fluid from the core tops was removed and analyzed for 613CDIC. The

supernatant fluid has 613CDIC values that range from -3.72 to -6.42%o (Table 3-1), which

could indicate that methane oxidation is occurring in the water column above seeps at

Monterey Bay and Eel River sites. An alternative explanation for the isotopically light

values of supernatant is that diffusion or advection of isotopically light DIC from the

sediments could enrich the water in 12C. Nonetheless, methanotrophic activity does occur

above seep sites in the Eel River basin and bacteria seem to oxidize methane soon after it

is released from the sediment (Valentine et al., 2001).

Bottom water 613CDIC values (collected 0.5 m above active seeps) ranged from

-2.26 to -4.53%o for cold seeps in the Gulf of Mexico (Aharon et al., 1992); these values

are similar to the supernatant values reported here, indicating the supernatant values

could represent bottom water values. Water samples were collected using a rosette,

deployed from the deck of the R/V Atlantis II, containing remote-tripping water

sampling bottles (Aharon et al., 1992). In contrast, bottom water values reported from

non-seep sites in the Pacific Ocean south of Pt. Sur varied from -0.19 to -0.29%o at the

two locations sampled (McCorkle et al., 1997). Bottom water samples were collected

using small Niskin bottles mounted on the corner of a box corer; the bottles were

engineered to close when the corer reached the seafloor (McCorkle et al., 1997).

Since there are few studies (of seep and non-seep sites) reporting both pore water

and foraminiferal isotopic data, U. peregrina is the species for which the most data is

available, among both prior research and this study; therefore it will be the only species









whose isotopic data is substituted into the equation for A613C. In addition, because

bottom water was not sampled for this study, when determining the value of A613C, both

estimated values of bottom water and values obtained using supernatant fluid are

compared for the Eel River and Monterey Bay cores.

Although no supernatant fluid was analyzed for the Invertebrate Cliffs or the

Clam Flats clam beds, supernatant fluid is available from other environments sampled at

these sites. At Invertebrate Cliffs, supernatant fluid was analyzed from the yellow

bacterial mat (located within the clam ring (Figure 2-1)); the fluid has a 613CDIC value of

-3.72%o, whereas supernatant fluid from a reference site at the Clam Flats clam bed has a

613CDIC value of -3.93%o. If these two values are substituted for bottom water in the

equation for A613C, resulting values for U. peregrina are approximately 3%o heavier than

values reported from other sites (Figure 4-4a). All U. peregrina show enrichment in 13C

relative to the supernatant DIC. If, however, an estimated bottom water value of-0.3%o

is used, the A613C values of the U. peregrina fall mostly within the range of reported

values, where U. peregrina are depleted in 13C relative to bottom water DIC (Figure 4-

4b). Still, the variation in the carbon isotopic composition of U. peregrina from methane

seeps at Monterey Bay is greater than that reported from non-seep sites.

Supernatant fluid for Eel River cores has 613CDIC values of -5.18 and -5.72%o

(Table 3-1), which contrasts markedly with estimated bottom water 613C values based on

Geosecs data, which Rathbum et al. (2000) report to be about -0.58%o for the Eel River

basin. When the 613CDIC values of the supernatant fluid from Eel River (Long Core (LC)

4 and LC 5) were substituted for bottom water and compared to U. peregrina carbon

isotopic compositions, A613C values varied significantly from those reported in the









literature. All U. peregrina had a positive A613C (Figure 4-5a); the values were

approximately between 1.75 and 6%o, compared to those reported in the literature, which

range from approximately -0.25 to -2%o (McCorkle et al., 1990; 1997; Rathburn et al.,

2000). The fossil U. peregrina from Clam bed 4, which had an average A613C that is

significantly lighter than those reported in the literature (as well as a much larger standard

deviation), were determined to be the result of authigenic carbonate contamination

(Rathburn et al., 2000).

When LC 4 and LC5 were replotted using the bottom water 613CDIC value (-0.58

%o) estimated by Rathburn et al (2000) for their sampling site (4047.08N, 12435.68W),

which is near the location of this study's sampling area, the average A613C values are in

good agreement with those reported in the literature (Figure 4-5b). Fossil (?) U.

peregrina from LC4 and LC5 have much larger standard deviations than all cores for

which data is available, except fossil U. peregrina from clam bed 4.

The Eel River cores analyzed contain some foraminifera, which have been

diagenetically altered, based on pore water saturation states, isotopic compositions, and

comparison to other seep and non-seep sites. The maximum standard deviation for all

species of foraminifera is 7.00%o. This value is larger than the excursions documented by

Dickens et al. (1995) who document a -2 to -3%o shift in 613C and 6180 values in benthic

foraminifera during the Paleocene, or the -5%o excursions during the Quaternary

documented by Wefer et al. (1994) and Kennett et al. (2000) off the coast of Peru and in

the Santa Barbara Basin, respectively. These large excursions may also include a

diagenetic component. The findings from this study show that the relationship between

methane and the 613C of foraminifera is not characterized by large excursions. Instead,








67



foraminifera from seepage sites have more variable carbon isotopic compositions, which


are similar to or approximately a mil or two lighter than foraminifera inhabiting non-seep


sites.


A13C (13C


1


13C bw) (%o PDB)


2


1780 PC30 (fossil)
1780 PC30 (fossil (?))
1780 PC30 (live)
1781 PC31 (fossil)

(a). 1781 PC31 (live)
Clam bed 5 (live)
Clam bed 5 (fossil)
Clam bed 4 (live)
PSII-BC207 (live)
PSII-BC213 (live)


--------------- ----I----
-------------- -
-- - -


----------I 1


--- -- ----------
-:1

- O


A13C (13C -13C bw) (%0 PDB)


1780 PC30 (fossil)
1780 PC30 (fossil (?))
1780 PC30 (live)
1781 PC31 (fossil)
1781 PC31 (live)
(b). Clam bed 5 (live)
Clam bed 5 (fossil)
Clam bed 4 (live)
PSII-BC207 (live)
PSII-BC213 (live)


-0.5 0

-,

--------- ------- ----------------
------------------------------------- -------


- I I








---------------------- ----------
--- --: -- -



---------------:---





---------------------------


- ---------- ------
-<---- -----------------------

--------------- -- -- -- -
- - -
', I S :


Figure 4-4(a, b). The average A613C and standard deviation (c) of U. peregrina from
Invertebrate Cliffs (1780 PC30) and Clam Flats (1781 PC31) compared to values
reported in the literature. (a). Actual bottom water 613C is not used; instead, the
supernatant fluid from the core tops is substituted for bottom water (See text for
discussion). Clam bed 5 and Clam bed 4 are seep sites in the Eel River Basin sampled by
Rathburn et al (2000). PSII cores are non-seep sites off the coast of California, south of
Pt. Sur (McCorkle et al., 1997). (b). An estimated bottom water value of -0.3%o is used
for the calculation of the average A613C from Clam Flats and Invertebrate Cliffs. Note
the difference in the scale of the x-axis from (a).


I I I







68



AC13C 13 13C b w ) (%0 PDB)


-10 -8 -6 -4 -2 0


CH90-BC5 (live)
CH90-BC4 (live)
PSII-BC207 (live)
PSII-BC213 (live)
(a).
Clam bed 5 (live)
Clam bed 5 (fossil)
Clam bed 4 (live)
Clam bed 4 (fossil)
LC4 (fossil (?))
LC5 (fossil (?))







CH90-BC5 (live)
CH90-BC4 (live)
PSII-BC207 (live)
(b). PSII-BC213 (live)

Clam bed 5 (live)
Clam bed 5 (fossil)
Clam bed 4 (live)
Clam bed 4 (fossil)
LC4 (fossil (?))
LC5 (fossil (?))


2 4 6


-
---- --- ------------- ---------- ----------------------- --------_---------








*





SI iiI I ,

A313 13C 13C b w 0(0 PDB)
-10 -8-- -6--- -4--- ---2 0 2
- ---------- -- -------- ------ -- --------------------- --------------------- -
---------- ----------- ---------- ----------- ------- ----------' ------------------ -- -














*
-
S------ ---
--- i- -- ------ -- I
-------- --------------
-- -- ----- --------------------------- ------------
------------------------------- ----------------------------- -------





I ----- I I I ------------ ------------- -
_------------------------ -------i--------- ^--


Figure 4-5(a, b). The average A613C and standard deviation of U. peregrina from Eel
River's Long core (LC) 4 (clam bed) and LC5 (bacterial mat), compared to those
reported in the literature. (a). LC4 and LC5 are plotted using 613CDIC values obtained
from supernatant fluid (see text for discussion). All PSII cores are from the Pacific Ocean
south of Pt. Sur, whereas CH90 cores are taken from the North Carolina slope north of
Cape Hatteras (McCorkle et al., 1997). Clam bed 5 and Clam bed 4 cores were collected
in the Eel River basin by Rathburn et al. (2000). (b) LC4 and LC5 are replotted using
Rathburn et al.'s (2000) bottom water 613CDIC value of-0.58%o.






69


Foraminiferal 6180 Compositions

Within Clam Flats, fossil foraminifera consistently display 6180 values that are

approximately 1.5%o heavier than live conspecifics (Figure 4-6), whereas the 613C values

of fossil species are less than 0.5%o lighter than their live counterparts (Figure 3-14,

Figure 3-15). Only a few overlapping oxygen isotopic values are seen and could result

from live specimens being inhabited by algae or nematodes, leading to a false 'live'

designation. In addition, most of the live foraminifera have oxygen isotopic values that

are similar to both live and fossil (?) foraminifera from Invertebrate Cliffs.


18O (%0 PDB)

3 3.5 4 4.5 5

o
1.5 -- --

2 0j U.peregrina (live)
2 --------------- -------- ---^* U p r g i a(i e
SO O U. peregrina (fossil)
S 2.5 o-------------- B. mexicana (fossil)
A B. mexicana (live)
3
3 A E. pacifica (fossil)
3.5 O A E. pacifica (live)
V E. smith (fossil)
4 ---- ---- ------- E. sm ithi (live)

4.5 ----------



Figure 4-6. A 6180 comparison of live and fossil conspecific foraminifera from Clam
Flats (1781 PC31). Note: E. pacifica values from 2.75 cm overlap and the live B.
mexicana (from 4.5 cm) is clustered with other live species around 3.15%o.


The 6180 values of the fossil foraminifera from Clam Flats places them within the

range of authigenic carbonate analyzed from the Clam Flats area, which Stakes et al.

(1999) determined to vary between 4.05 and 5.19%o. The 613C values of these same









authigenic carbonates range from -48.82 to -52.60%o (Stakes et al., 1999). If authigenic

carbonate overgrowths, such as those found by Stakes et al. (1999) were to account for

the 1.5%o increase in 6180, the resulting decrease in 613C would be between -13 and

-18%o, as somewhere between 28 and 35% of the oxygen isotopic composition would

have to be provided by authigenic carbonate. Although pore fluid chemistry could have

varied significantly over time, the isotopic composition of numerous fossil foraminifera

(of various species) is consistent; therefore, it is unlikely that even multiple stages of

authigenic carbonate formation could explain the disparity in 6180 between live and fossil

foraminifera.

One explanation for the disparity between fossil and live foraminifera from Clam

Flats is that the fossil foraminifera are remnants from a colder time, perhaps the Last

Glacial Maximum (LGM), exposed by an erosional event. Barry et al. (1996) noted the

Clam Flats site was characterized by clams inhabiting small shallow depressions.

Additionally, clams were noted to form aggregations along the lower edges of small,

meter-scale scarps (Barry et al., 1996). As slumping occurs, foraminifera inhabiting the

sediment will be displaced. With later recolonization of the site, live foraminifera would

inhabit sediment containing older, fossilized foraminifera; these fossilized foraminifera

could have secreted their tests under very different temperature conditions, perhaps

during glacial times, when deep water was older and had lower 613C and cooler

temperatures would have contributed to heavier 6180 compositions. Furthermore,

seawater 6180 would have been heavier due to the glacial sequestering of isotopically

light ice. According to Curry et al. (1988), the 6180 of the deep water in the Pacific

Ocean during the LGM was between 3.86 0.06%o and 4.35 0.02 %o. In addition, the









oxygen isotopic difference between the LGM and present (expressed as glacial -

interglacial) is between 1.33 and 1.67%o (Curry et al., 1988). Likewise, the LGM had

deep-water 613C values that were between 0.21 and 0.60%o lighter than present 613C

values (Curry et al., 1988). These offsets correlate nicely with the isotopic offsets

between fossil and live foraminifera from Clam Flats.

A Comparison of Foraminiferal Oxygen Isotopes from Seep and Non-seep Sites

Living foraminifera from different areas can be compared if calcite in equilibrium

with bottom water 6180 values are subtracted from foraminiferal 6180 values, yielding a

value termed A6180 (McCorkle et al., 1990; 1997; Rathburn et al., 1996). For Monterey

Bay, the value for calcite in equilibrium with bottom water 6180 was taken from Stakes et

al. (1999), who calculate a 6180 value of approximately 3.2%o for a temperature of 4 C,

which is approximately the same bottom water temperature as this study. Living

foraminifera from both Invertebrate Cliffs and Clam Flats fall within the range of A6180

values reported in the literature (Figure 4-7). In addition, fossil foraminifera from

Invertebrate Cliffs also fall within the reported range, excluding two U. peregrina values.

Fossil foraminifera from Clam Flats, however, fall outside the reported range, with values

varying from 1.29 to 1.63%o, providing further confirmation that these foraminifera

secreted their tests under different bottom water conditions than live foraminifera

inhabiting the same sediment.

In the Eel River basin, sites sampled during this study are close to and in similar

water depths (-500 m) to those sampled by Rathburn et al. (2000), who estimated a

bottom water 6180 in equilibrium with calcite value of 2.35%o. The average A6180 values

for Eel River fossil foraminifera are heavier than the fossil values reported by Rathburn et











A180 (%o PDB)
-0.5 0 0.5 1 1.5 2

1780 PC30 (fossil ?) -------------
1780 PC30 (live) ------
1781 PC31 (live)------ -
1781 PC31 (fossil) ---------------------------------
PSII-BC207 (live) -----------
PSII-BC213 (live) -- -
Clam bed 5 (live) --------------- -------- -----------------
C lam bed 5 ( oss l) --- --- --- --- ---------------------^------------- ---------------- ------------------
Clam bed 5 (fossil) --------
Clam bed 4 (live)------------------- ------
Clam bed 4 (fossil) -

Figure 4-7. A plot of the A6180 values of U. peregrina from Invertebrate Cliffs (1780
PC30) and Clam Flats (1781 PC31) relative to those values reported in the literature.
PSII cores are from south ofPt. Sur (McCorkle et al., 1997). Clam bed 5 and Clam bed 4
are from the Eel River Basin (Rathburn et al., 2000).


al. (2000) (Figure 4-8). In addition, many are heavier than the only 6180 value reported

for authigenic carbonate from the area, which had a 6180 value of 3.79%o and a 613C

value of -33.57%o (Rathburn et al., 2000).

It has been previously discussed that the isotopic variability found throughout the

Eel River cores is in part due to diagenesis, which is also masking variability caused by

hydrate dissociation (and the subsequent bacterial oxidation of methane). Because Eel

River sites sampled near the boundary of the hydrate stability zone, hydrate dissociation

could be causing variations in the 6180 of pore fluids. The lattice composing methane

hydrates preferentially incorporates 0O, therefore, upon dissociation, fluids containing

hydrates would be isotopically heavier than fluids not influenced by hydrate dissociation.

For instance, Aharon et al. (2001) determined that methane hydrate dissociation has led

to a maximum 80 enrichment of 1.7 %o in Bolivina species in the Gulf of Mexico. The

timing of hydrate dissociation and test calcification could create isotopic variability,








73



however, because live foraminifera were not analyzed, determining the relative


contribution of these processes is impossible.


A8O80 (%o PDB)


2052 Long Core 5 (fossil ?)

2052 Long Core 4 (fossil ?)

2052 Long Core 2 (fossil ?)

Clam bed 5 (live)

Clam bed 5 (fossil)

Clam bed 4 (live)

Clam bed 4 (fossil)

PSII-BC207 (live)

PSII-BC213 (live)


-----------
----------------


-- ^ -i---------------





.^.-----------------
---------



- -


--------------

.-----------I------ _]
--------------




I----------1-------------^--
-----------~------- -------------;---



-----------------


-I


Figure 4-8. A plot of the A6180 values of U. peregrina from Eel River (2052) LC5
(bacterial mat), LC4 (clam bed) and LC2 (bubble site) relative to those values reported in
the literature. PSII cores are from south ofPt. Sur (McCorkle et al., 1997). Clam bed 5
and Clam bed 4 are from the Eel River Basin (Rathburn et al., 2000).














CHAPTER 5
CONCLUSIONS



Methane seepage and its ensuing oxidation by bacteria produces isotopically light

DIC in pore waters. In addition, methanotrophic activity creates a favorable environment

for the precipitation of authigenic minerals; increases in alkalinity and sulfide could result

in the precipitation of carbonate and iron minerals, particularly pyrite. In addition, the

degrading protoplasm of dead foraminifera may provide a nucleus for mineral growth

(Berner, 1980). Because seepage is likely episodic, pore fluid saturation states could vary

temporally, increasing the diversity of isotopic signals found at seep sites. Therefore,

careful attention needs to be paid to fossil benthic foraminifera being used to assess the

history of methane seepage; as variation in the carbon isotopic composition will be

overshadowed by diagenetic effects. Live foraminifera should be analyzed whenever

possible to estimate the relative isotopic contribution of methane seepage and possibly

diagenesis to fossil foraminiferal carbonate.

This study shows that methane seepage creates carbon isotopic variability in

benthic foraminiferal tests; the negative carbon isotopic signal which is imparted on the

test is not more than a few per mil. Foraminifera living in the 13C-depleted environment

of seeps did not develop 613C values in their tests that were similar to pore water values,

which had carbon isotopic values as light as -37%o in the upper 5 cm of a core.

Therefore, although methane seepage does create steeper decreases in 613CDIc with depth

than profiles containing organic matter oxidation alone, isotopic differences between
74









epifaunal and infaunal species are not enhanced by more than 1 or 2%o relative to non-

seep species. Large negative carbon isotopic excursions, like those seen in Eel River

foraminifera, appear to result from authigenic carbonate contamination; however, live

foraminifera, which would help quantify the variability contributed by methane seepage,

were not analyzed. Additional studies on the variability of foraminiferal carbon isotopes

in seep and non-seep environments would enable a more complete characterization of the

effects of methane seepage on benthic foraminifera.

Based on the available data from non-seep environments, it appears that the

carbon isotopic composition of benthic foraminifera from seep sites is similar or more

negative than non-seep foraminifera. However, bottom water samples need to be

collected and analyzed for 613CDIC to determine if the A613C equation can be used to

compare seep and non-seep foraminifera. Additionally, bottom water samples must be

collected from seep sites to determine whether DIC values in the waters above seeps are

as 13C depleted, up to -4.5%o, as those reported by Aharon et al. (1992). Looking at

epifaunal foraminifera, such as Planulina species, which are believed to secrete their test

in isotopic equilibrium with bottom waters (at least in non-seep environments) would

allow for a better characterization of bottom water chemistry and enable conclusions to

be drawn on the ability of seep fluxes to alter bottom water composition.

Although a microhabitat effect does exist in seep settings and pore water

composition does influence benthic foraminiferal composition, it appears that pore water

plays a larger role in creating isotopic variability than it does in imparting negative

isotopic signatures on foraminifera. For instance, in non-seep sites, U. peregrina had

carbon isotopic compositions that were nearly equal to the pore water concentration in









the upper 0.5 cm of the sediment (McCorkle et al., 1997). This, however, was not the

case for the seep environments sampled during this study; the 613C of U. peregrina, on

average, was between 4 and 18 times heavier than pore water 613CDIC. This

disequilibrium could indicate that the foraminifera have specific microenvironments

where calcification takes place, possibly near the surface or near burrows where seawater

DIC (613CDIC approximately 0%o) would contribute more to the DIC pool.

Sediments containing pore waters that have isotopically lighter carbon signatures

also contain foraminifera with more variable carbon isotopic compositions. It is,

however, impossible to know the pore water conditions under which these foraminifera

calcify their tests. Nonetheless, foraminifera are incorporating a portion of DIC derived

carbon into their tests, which creates isotopic variability among foraminifera as pore

water chemistry changes.

















APPENDIX A
PORE WATER CHEMISTRY


Dive Push Core f Alkalinity Ca Mg S04 HS
Number Location No. (mM) pH (mM) (mM) (mM) (mM)


0.5
2.0
4.0
34 6.0
8.0
10.0
12.0


13.59
14.97
16.72
15.91
17.61
19.89
17.83


7.39 17.1
7.41 18.9
7.20 18.3
7.46 19.1
17.2
17.0
7.92 16.1


0.5 2.59 7.40 11.8
2.0 2.74 7.28 11.3
4.0 2.66 11.2 0.2
79 6.0 3.01 7.60 11.8 0.5
8.0 3.14 7.65 11.5 0.6
10.0 3.38 7.87 11.3 1.1
12.0 3.61 7.87 11.8
0.5 3.39 12.9 1.1
2.0 7.34 7.93 13.3 1.0
4.0 13.57 8.02 13.0 2.2
31 6.0 16.22 14.1 2.3
8.0 19.57 7.65 15.3 2.2
10.0 20.03 7.71 17.2 2.3
12.0 20.56 16.3 1.9


(U
c)


k
9
d



d
(U


>






.+a
-


7.32 10.7
7.31 11.3
7.40 12.0
7.32 11.7
7.30 11.1
7.46 12.1
7.57 10.8
7.49 11.2
11.7
7.49 11.2


SMonterey 0.5 11.10 11.2 4.3
S Bay- 80 2.0 19.47 10.3 7.9
r- Clam Flats
4.0 31.80 9.0 15.4


0.5
2.0
4.0
6.0
38 8.0
38
10.0
12.0
14.0
16.0
18.0











Dive Push Core Alkalinity Ca Mg S04 HS
Number Location No. cm-bsf (mM) pH (mM) (mM) (mM) (mM)
Number No. (mM) (mM) (mM) (mM) (mM)


6.0
8.0

80 10.0
12.0
14.0
16.0


34.27
32.30
37.55
38.82
35.35
36.92


0.5 2.82 11.8 0.7
2.0 2.81 10.7
4.0 3.8
72 6.0 2.90 10.1
11.0 3.09 11.4 0.8
16.0 2.27 10.7
21.0 4.03 10.6 0.3
0 2.50 7.59
0.5 2.92 7.66 11.3 0.5
2.0 2.94 7.55 11.1
38 4.0 2.77 7.73 10.6 0.6
6.0 2.74 7.99 10.8
11.0 3.52 8.18 12.9
13.0 1.4


cl







O)


0


0
0.5
1.5
8 2.5
3.5
4.5
5.5
6.5


0
0.5
1.5
16 2.5
16
5.5
6.5
8.5
11.5


3.03
4.60
22.93
28.68
25.28
24.77
30.07
28.93


7.70 14.4
10.9
8.34 9.2
8.1
8.47 7.5
8.45 7.4
8.47 8.5
8.6


2.50
3.90
4.40
5.80
6.80
8.30
11.20
17.30


2.50
3.20


4.80


15.40
25.30
32.60


51.6 27.9
49.1 27.1
48.7 26.6
48.8 25.4
48.7 24.5
49.4 23.9
51.7 22.5
45.4 14.5


9.8
7.52 9.5
9.1
8.43 8.7
5.5
8.23 7.1
8.14 5.8
3.9


51.6
49.6 29.5
49.2 28.2
50.7 27.5
46.3
47.2 22.2
47.2 18.5
46.7 10.5


0.5
2.0
4.0
28 6.0
28
8.0
10.0
12.0
14.0














Dive Push Core f Alkalinity Ca Mg SO4 HS
Number Location No. (mM) pH (mM) (mM) (mM) (mM)

13.5 30.80 8.21 1.4 46.4 9.3 13.1

16 15.5 32.10 8.21 2.1 46.1 5.2 13.5
17.5 32.40 8.29 1.3 46.1 4.1 12.7
19.5 33.70 8.34 0.9 51.4 3.4 13.8
0 2.50 9.6 50.9 27.5
^ 0.5 4.60 7.78 9.6 50.4 26.3 0.5
C1 1.5 9.60 7.90 9.0 49.0 22.1 3.7
2.5 14.00 8.12 10.8 61.5 6.0
CN 3.5 18.30 8.10 8.4 48.6 15.1 8.4
19 4.5 22.10 8.24 5.9 45.7 10.4 8.5
6.5 28.00 8.22 3.2 45.2 4.5 11.3
10.5 36.10 8.22 2.0 42.5 0 16.1
12.5 35.60 8.19 1.5 45.3 0
14.5 36.50 8.22 0.9 45.0 0 14.7
16.5 35.00 8.34 0.7 45.9 0 15.6
0 2.50 9.6 50.3 0.0
0.5 17.60 9.0 47.8 23.3 6.2
1.5 20.90 8.44 9.3 52.2 19.1 6.9
2.5 24.50 8.61 4.8 53.3 6.9
2 3.5 22.30 8.34 6.8 45.4 19.6 7.5
4.5 25.30 8.37 3.0 44.2 14.4 7.6
5.5 29.50 8.36 2.8 48.6 9.3 8.4
6.5 31.50 8.46 1.5 44.9 6.3 6.5
S7.5 29.40 8.18 1.0 45.0 6.4 6.4
0 2.27 10.3 52.7 28.2 0.0
C 0.5 2.70 7.27 9.8 49.4 28.7 0.0
1.5 3.00 7.59 9.4 48.7 28.7 0.0
2.5 5.40 7.95 9.4 48.0 28.3 0.8
40 3.5 7.40 7.98 9.3 47.8 26.9 1.6
4.5 9.80 8.10 9.1 47.5 24.4 3.2
5.5 11.00 8.15 7.9 46.6 26.7 2.2
6.5 16.40 8.20 6.8 46.0 21.7 5.0
7.5 17.20 8.29 5.5 54.5 23.3 4.9











Dive Push Site
Dive Location Push Site Interval (cmbsf) 13CDIC
Number Core Description


-4.60
-3.63
-4.42
-4.49
-4.48
-4.69
-4.91
-4.87
-6.09


9-11
11-13
11-13
15-17


Core top supernatant -3.72
S0-1 -7.60
S1-3 -15.22
3-5 -18.55
5-7 -21.07
o 7-9 -22.79
9-11 -22.69
11-13 -22.00
0-1 -12.77
S1-3 -13.33
3-5 -15.09
5-7 -15.98
7-9 -18.68
9-11 -21.00
11-13 -21.16


0-1
1-3
3-5
3-5
5-7
7-9
9-11
11-13


-4.78
-4.12
-4.44
-4.40
-5.75
-6.48
-7.52
-8.58


Core top supernatant
0-1
1-3
3-5
17-19


-3.93
-5.46
-6.85
-6.99
-21.62


C) 0-1 -13.79
00 3-5 -58.15
"00 CG 5-7 -56.80
9-11 -49.54
11-13 -47.65
_13-15 -47.06
0 0-1 -36.47
00 1-3 -45.73
9-11 -41.48











Dive Push Site
Dive Location Push Site interval (cmbsf) 13CDIC
Number Core Description
o Clm Bd 9-11 -43.95
0 Clam Bed15-17 -42.39
Q -. 1-3 -8.21
5I o g 3-5 -5.81
5-7 -7.06
S10-12 -11.24
C 15-17 -13.20
__20-22 -10.95


Core top superatant
0-1
2-3
4-5
6-7


-5.72
-13.51
-22.36
-27.09
-33.95


Core top superatant -5.18
0-1 -9.16
2-3 -24.06
(N -6-7 -37.36
S8-9 -38.47
(NI 13-14 -39.08
15-16 -37.85
19-20 -38.81
c0-1 -17.83
S2-3 -31.97
S4-5 -37.78
10-11 -33.49
12-13 -32.03
16-17 -30.83
Core top superatant -6.42
0-1 -25.17
2-3 -23.86
4-5 -23.19
U 6-7 -19.58
I 7-8 -18.15
CI 0-1 -9.02
2-3 -18.91
C 4-5 -25.76
t 6-7 -30.57
7-8 -32.06



















APPENDIX B
FORAMINIFERAL ISOTOPE DATA


DIVE TUBE- DEPTH 13 18 NO. OF LIVE/
NUMBER SITE CORE (cm-bs) SPECIES 8 C 80 INDIVIDUALS
RUN FOSSIL


Gyroidinoides ,ioir a-. .i
Uvigerina peregrina
Uvigerina peregrina
Bulimina mexicana


Uvigerina peregrina
Uvigerina peregrina
Uvigerina peregrina
Uvigerina peregrina
Bulimina mexicana
Bulimina mexicana
Uvigerina peregrina
Uvigerina peregrina
Uvigerina peregrina
Uvigerina peregrina
Globobulimina pac itica
Planulina sp.


-0.70 3.15
-1.36 3.09
-1.18 4.04
-1.03 3.80


-1.34 4.63
-1.03 4.83
-1.35 4.62
-1.85 4.49
-1.04 4.89
-2.24 4.65
-0.89 3.11
-0.62 3.21
-0.43 3.12
-0.69 3.12
-3.87 3.42
-0.22 2.63


Epistominella pai it a -1.09 4.61 2 FOSSIL
Epistominella pi itha -1.11 4.65 2
Uvigerina peregrina -0.55 3.16 0.5
Uvigerinaperegrina -0.49 3.28 1
cq Uvigerinaperegrina -0.74 3.21 1
tii Uvigerinaperegrina -0.22 3.25 1
Uvigerinaperegrina -0.21 3.21 0.5
Uvigerinaperegrina -0.57 3.15 1 0
Uvigerina peregrina -0.97 3.10 0.5
Gyroidinoides, i' a.... -0.83 3.14 2
Gyroidinoides ,aiir' a..' -0.66 3.11 1


Uvigerina peregrina
Uvigerina peregrina
Uvigerina peregrina
Bulimina mexicana
Uvigerina peregrina
Uvigerina peregrina
Uvigerina peregrina
Uvigerina peregrina
Uvigerina peregrina
Uvigerina peregrina


-1.57 4.58
-1.04 4.65
-1.31 4.58
-1.19 4.72
-2.05 3.04
-1.13 3.17
-0.81 3.21
-1.14 3.07
-0.94 3.12
-0.10 3.43


C)
V4
04












DIVE TUBE- DEPTH NO. OF LIVE/
NUMBER SITE CORE SPECIES 613C 8180 INDIVIDUALS
NUMBER CORE (cm-bsf) RUN FOSSIL


Epistominella smith
Globobulimina pai iic a
Epistominella pat itc a
Epistominella pint itl a
Epistominella p itic a
Uvigerina peregrina
Uvigerina peregrina
Uvigerina peregrina
Uvigerina peregrina
Uvigerina peregrina
Epistominella smith
Gyroidinoides ,,ahi. ..... .
Gyroidinoides ,,ahi. ..... .
Epistominella put itc a
Epistominella piut itll a
Epistominella tn it c a


-0.92 3.57
-3.49 3.30
-0.92 3.15
-1.20 4.59
-1.19 4.61
-1.82 3.18
-1.12 3.15
-0.25 3.21
-0.75 3.25
-1.39 3.27
-0.60 3.11
-0.66 3.11
-0.45 3.13
-0.99 4.56
-1.02 4.63
-1.01 4.66


FOSSIL


m Planulina sp. 0.06 2.60 0.5
S Planulina sp. 0.45 2.86 1.0
S Planulina sp. 0.07 2.60 0.5
Uvigerinaperegrina -2.03 4.62 2
Uvigerinaperegrina -1.40 4.73 1
Uvigerina peregrina -1.30 4.58 1
Bolivina spissa -1.80 4.55 3 41
Bolivina spissa -1.54 4.75 3
t- Uvigerina peregrina -1.17 3.15 1
S Uvigerinaperegrina -0.83 3.22 1
Uvigerina peregrina -1.82 3.09 1
Uvigerina peregrina -1.30 3.14 0.5
Uvigerinaperegrina -0.72 3.16 0.5
Uvigerina peregrina -1.04 3.12 0.5
Gyroidinoides ,ii.'a .... -0.85 3.06 1
Bulimina mexicana -1.06 3.30 4


Epistominella smith
Epistominella smith
Uvigerina peregrina
Uvigerina peregrina
Uvigerina peregrina
Uvigerina peregrina
Uvigerina peregrina
Bulimina mexicana
Bulimina mexicana
Gyroidinoides ,,ai. ihi11
Epistominella smith


-1.00 4.57
-1.89 4.64
-1.40 4.64
-1.21 4.78
-1.04 4.82
-1.36 4.58
-1.92 4.59
-1.18 4.71
-1.51 4.71
-0.67 3.18
-0.63 3.22


Gyroidinoides neosoldani -0.67 3.12 2
Gyroidinoides neosoldani -0.57 3.28 1
Gyroidinoides neosoldani -0.49 3.40 1


<





<
F.
uC,.


'4

00

'4











NO. OF LIVE/
DIVE TUBE- DEPTH NO.OF LIVE/
VE SITE UBE- DEPTH SPECIES 813C 5180 INDIVIDUALS
NUMBER CORE (cm-bsf) RUN FOSSIL

Globobulimina barbata -5.36 4.52 2
Globobulimina barbata -2.77 4.47 2
Globobulimina pa iic a -4.56 3.20 2
c Uvigerina peregrina -0.95 3.14 2
Uvigerinaperegrina -1.53 3.14 2
-) [ Uvigerinaperegrina -0.78 3.07 2
SUvigerina peregrina -0.78 3.28 1
Uvigerinaperegrina -1.05 3.23 1
Uvigerinaperegrina -0.86 3.23 1
Uvigerina peregrina -0.51 3.13 1
Bulimina mexicana -1.17 3.22 6
Buliminella tenuata -2.76 4.40 3


Uvigerina peregrina
Uvigerina peregrina
Uvigerina peregrina
Uvigerina peregrina
Globobulimina pac iic a
Globobulimina pi ific a
Globobulimina pi itic a
Globobulimina pc ific a
Epistominella put iitl a
Epistominella put iitc a
Bulimina mexicana


-0.85 2.83
-0.54 3.01
-0.32 3.19
-0.71 3.06
-0.92 3.28
-1.36 3.28
-0.74 3.30
-1.46 3.28
-0.79 3.09
-0.73 3.10
-0.82 3.26


Uvigerinaperegrina -0.43 3.01 1
Uvigerina peregrina -0.76 3.16 1
Uvigerinaperegrina -0.57 3.25 1
t- Globobulimina pad iic a -1.29 3.45 1
Globobulimina piaitkca -1.84 3.33 2
Globobulimina pai ifica -1.43 3.25 1
Globobulimina paiticia -0.91 3.49 1
Epistominella pitiitc a -0.78 3.30 3
Epistominella pa iti a -0.53 3.11 4
Bulimina mexicana -0.70 3.26 2
Uvigerinaperegrina -0.56 3.09 1
Uvigerinaperegrina -0.51 3.03 1
I Uvigerinaperegrina -0.49 3.07 1
Epistominella p ut it a -0.50 3.22 3
E'. Epistominella pui t i a -0.72 3.23 4
Globobulimina pat itica -2.14 3.39 2
Globobulimina pi ticia -2.17 3.35 2
Bulimina mexicana -0.72 3.29 2


Uvigerina peregrina
Uvigerina peregrina
Epistominella pti itc a
Epistominella put itl a
Epistominella pac itc a
Globobulimina pai iic a


-0.47 3.20
-0.50 3.01
-0.73 3.14
-0.63 3.17
-0.59 3.15
-1.98 3.33


00
cc












DIVE TUBE- DEPTH NO.OF LIVE/
SITE SPECIES 813C 5180 INDIVIDUALS
NUMBER CORE (cm-bsf) RUN FOSSIL


Globobulimina pac itic a
Globobulimina pai itic a
Globobulimina pi itic a
Bulimina mexicana
Planulina sp.
Uvigerina peregrina
Uvigerina peregrina
Uvigerina peregrina
Epistominella pi itic a
Epistominella piut itic a
Epistominella piul itic a
Globobulimina pac ific a
Globobulimina pac ific a
Globobulimina pac itic a
Bulimina mexicana
Planulina sp.
Globobulimina attini\


-1.15 3.38
-0.92 3.34
-0.41 3.38
-0.80 3.30
0.04 2.80
-0.57 3.23
-0.77 3.23
-0.27 3.11
-0.53 3.15
-0.63 3.29
-0.60 3.21
-1.20 3.33
-1.68 3.41
-2.23 3.27
-0.70 3.29
0.09 2.95
-0.90 3.29


Epistominella smith -0.59 3.15 2
Epistominella smith -0.76 3.19 4
Bulimina mexicana -0.85 3.28 4
Globobulimina cifticia -1.06 3.28 1
Globobulimina piaitica -0.91 3.29 2
S Globobulimina paKifia -1.72 3.25 3
Globobulimina pat ifi a -1.22 3.27 2
Uvigerinaperegrina -0.33 2.97 1
Uvigerinaperegrina -0.78 2.87 1
Uvigerinaperegrina -0.36 3.26 1
Uvigerinaperegrina -0.59 2.98 1
Epistominella smith -0.40 3.18 1
Epistominella smith -0.45 3.30 1
C Epistominella smith -0.35 3.18 1
" Uvigerinaperegrina -0.65 3.06 2 0
Uvigerinaperegrina -0.95 3.20 2
Bulimina mexicana -0.83 3.33 3


Epistominella smith
Epistominella smith
Epistominella smith
Epistominella smith
Epistominella smith
Epistominella smith
Bulimina mexicana
Bulimina mexicana
Bulimina mexicana
Globobulimina pai itica
Globobulimina pac ifi a
Globobulimina pac ifi a
Globobulimina pac ific a


-0.58 3.06
-0.43 3.16
-0.70 3.20
-0.48 3.16
-0.76 3.07
-0.77 3.06
-0.92 3.36
-0.81 3.20
-0.89 3.28
-0.93 3.30
-1.81 3.23
-1.34 3.26
-1.47 3.33











DIVE TUBE- DEPTH NO. OF LIVE/
E SITE SPECIES 813C 8180 INDIVIDUALS
NUMBER CORE (cm-bsf) RUN FOSSIL

Uvigerinaperegrina -0.59 2.59 1
Uvigerina peregrina -0.04 3.11 1
Uvigerinaperegrina -0.45 2.91 1
V,) 0 Uvigerinaperegrina -0.43 3.14 1
S" Uvigerina peregrina -0.36 3.40 1
Uvigerinaperegrina -0.37 3.15 1
H Uvigerina peregrina -0.36 3.10 1
Uvigerinaperegrina -0.49 2.66 1

00 pistominella smith -0.72 3.31 4 LIVE
SGlobobulimina pacitica -1.22 3.34 3
< pistominella smith -0.66 3.19 3 FOSSIL
i- ) Uvigerinaperegrina -0.61 3.13 3
S Uvigerinaperegrina -0.80 3.16 1
SGlobobuliminapacilica -1.12 3.19 2
SG__lobobulimina ac itica -1.50 3.25 2
C Epistominella piaitK a -0.59 3.21 4
S Uvigerina peregrina -1.04 3.14 1
__ 2.5-3 Epistominella apc iti a -0.62 3.19 2



Hydraulic No. of
Dive No. Site Push Core Depth- Species (all are fossil (?)) 8C 880 individuals
(cm-bsf)
No. run
Planulina sp. 0.13 2.55 1
7= Bulimina mexicana -0.72 3.26 3
,- Uvigerina peregrina -0.70 3.26 1
0.5 Uvigerina peregrina -0.95 3.17 4
Epistominella pacifica -0.50 3.22 1
SEpistominella pacifica -0.41 3.47 1
Epistominella pacifica -0.47 3.48 1
Uvigerina peregrina -0.30 3.06 0.5
0 Uvigerina peregrina 0.01 3.22 0.5
00
r I) 1.5 Uvigerina peregrina -0.12 3.27 0.5
Epistominella pacifica -0.64 3.34 2
Epistominella pacifica -0.52 3.24 2
2.5 Epistominella pacifica -0.42 3.35 1
>Epistominella pacifica -0.33 3.23 1
p Epistominella pacifica -0.52 3.20 1
4 Bulimina mexicana -1.04 3.28 2
Bulimina mexicana -1.00 3.05 2
Globobuliminapacfca -0.73 3.33 3
SGlobobulimina pacifica -0.73 3.33 3
__Globobulimina pacifica -0.78 3.38 3











Hydraulic
Dive No. Site Push Core
No.


0
I'D
-o

d)



0
E




*-



0
d)
(D


(D
0




0

0
d





(D
-

(D

.+,,

d)
0,


pth No. of
(cm-bsf) Species (all are fossil (?)) 8"C 180 individuals
(cm-bsf)
run
S Buliminella tenuata -1.59 2.98 1
Uvigerina eregrina -0.35 3.33 1
Uvigerina peregrina -0.35 3.33 1
Uvigerina peregrina -0.60 3.36 1
Buliminella tenuata -1.85 3.03 2
Bulimina mexicana -0.91 3.72 2
Epistominella pacifica -0.52 3.26 2
7.5 Epistominella pacifica -1.06 3.03 3
8.5 Epistominella pacifica -0.78 3.51 1
9.5 Epistominella pacifica -0.43 3.24 1
Epistominella pacifica -0.50 3.20 1
Epistominella pacifica -0.27 3.19 1
10.5 Uvigerina peregrina -0.22 3.12 0.5
Globobulimina pacifica -1.37 3.36 2
Uvigerina peregrina -0.25 3.25 1
Globobulimina pacifica -1.04 3.31 1
Globobulimina pacifica -1.03 3.40 1
Epistominella pacifica -0.41 3.28 1

11.5 Epistominella pacifica -0.27 3.27 1
Uvigerina peregrina -0.75 3.24 1
Uvigerina peregrina -0.83 3.34 2
Uvigerina peregrina -0.44 3.09 0.5
Uvigerina peregrina -0.66 3.22 0.5
Uvigerina peregrina -1.00 3.15 3
12.5 Epistominella pacifica -0.47 3.19 1
Epistominella pacifica -0.39 3.22 1
Globobulimina pacifica -1.17 3.61 2
Uvigerina peregrina -0.28 3.48 1
Uvigerina peregrina -0.51 3.24 1
13.5
Bulimina mexicana -0.84 3.68 3
Epistominella pacifica -0.40 3.19 1
Epistominella pacifica -0.43 3.34 1
Uvigerina peregrina -0.94 3.23 2
Uvigerina peregrina -0.50 3.36 1
Uvigerina peregrina -0.62 3.22 0.5
Uvigerina peregrina -0.51 3.12 0.5
Bulimina mexicana -0.73 3.51 2
14.5 Bulimina mexicana -0.71 3.49 2
Epistominella pacifica -0.36 3.21 1
Epistominella pacifica -0.13 3.54 1
Epistominella pacifica -0.47 3.16 2
Globobulimina pacifica -1.08 3.37 2
Globobulimina pacifica -1.11 3.40 2
15.5 Globobulimina pacifica -1.03 3.26 1
Uvigerina peregrina -0.25 3.20 1











Hydraulic D h No. of
Dive No. Site Push Core D(cm- Species (all are fossil (?)) 81C 860 individuals
No. run


Uvigerina peregrina

15.5 Epistominella pacifica
Epistominella pacifica
Buliminella tenuata


Buliminella tenuata
Uvigerina peregrina
Epistominella pacifica
Epistominella pacifica
Epistominella pacifica
16.5 Epistominella pacifica
Epistominella pacifica
Epistominella pacifica
Epistominella pacifica
Epistominella pacifica
Epistominella pacifica
Epistominella pacifica


-0.08 3.10
-0.33 3.35
-0.51 3.46
-1.36 3.54


-1.09 3.50
-0.91 3.22
-0.39 3.29
-0.31 3.40
-0.46 3.43
-0.47 3.29
-0.45 3.32
-0.54 3.07
-0.44 3.46
-0.39 3.36
-0.57 3.13
-0.34 3.37


17.5 Epistominella pacifica -0.50 2.31 1
Epistominella pacifica -0.31 3.60 1
Epistominella pacifica -0.50 3.23 1
18.5 Epistominella pacifica -0.39 3.40 1
Epistominella pacifica -0.39 3.34 1
Epistominella pacifica -0.39 3.25 1
19.5 Epistominella pacifica -0.42 3.34 1
Bulimina mexicana -0.56 3.52 1
Uvigerina peregrina -0.72 3.40 1
Uvigerina peregrina -0.87 3.32 3
20.5 Epistominella pacifica -0.26 3.27 1
Epistominella pacifica -0.40 3.53 1
Buliminella tenuata -1.05 3.29 2


Buliminella tenuata
Buliminella tenuata
Buliminella tenuata
Buliminella tenuata
Planulina sp.
Planulina sp.
Epistominella pacifica
21.5 Epistominella pacifica
Uvigerina peregrina
Uvigerina peregrina
Bulimina mexicana
Bulimina mexicana
Globobulimina pacifica
Globobulimina pacifica
Globobulimina pacifica


-1.45 3.39
-0.81 3.41
-0.93 3.43
-1.54 3.25
0.22 2.70
0.26 2.50
-0.41 3.29
-0.23 3.36
-0.82 3.36
-0.77 3.08
-0.97 3.28
-0.69 3.14
-1.35 3.37
-1.07 3.30
-0.90 3.40











Hydraulic
Dive No. Site Push Core
No.


pth No. of
(cm-bsf) Species (all are fossil (?)) 8"C 180 individuals
(cm-bsf)
run
Globobulimina pacifica -0.81 3.49 3
21.5 Globobulimina pacifica -1.08 3.37 1
Globobulimina pacifica -0.97 3.40 1
Uvigerina peregrina -0.55 3.15 1
Uvigerina peregrina -0.71 3.25 1
Bulimina mexicana -0.87 3.49 2
22.5 Bulimina mexicana -0.56 3.42 2
Globobulimina pacifica -0.61 3.38 1
Globobulimina pacifica -1.07 3.33 1
Buliminella tenuata -1.82 3.64 1
Epistominella pacifica -0.34 3.31 1
Bulimina mexicana -0.57 3.64 1
Bulimina mexicana -0.69 3.39 3
Epistominella pacifica -0.44 3.22 1
Epistominella pacifica -0.21 3.16 1
23.5 Buliminella tenuata -1.35 3.18 3
Buliminella tenuata -1.43 3.17 2
Globobulimina pacifica -1.69 3.42 1
Globobulimina pacifica -1.04 3.29 2
Uvigerina peregrina -0.97 3.25 5
Epistominella pacifica -0.49 3.24 1
24.5 Epistominella pacifica -0.51 3.25 2
Bulimina mexicana -0.71 3.37 2
Bulimina mexicana -0.52 3.89 2
Uvigerina peregrina -0.60 3.73 1
25.5 Uvigerina peregrina -1.05 3.12 1
Epistominella pacifica -0.50 3.28 2
Epistominella pacifica -0.50 3.34 2
Buliminella tenuata -1.27 3.29 2
Uvigerina peregrina -0.72 3.28 2
26.5 Epistominella pacifica -0.32 3.15 1
Epistominella pacifica -0.29 3.15 1
Globobulimina pacifica -1.09 3.35 1
Globobulimina pacifica -1.19 3.42 1

27.5 Epistominella pacifica -0.32 3.30 1
Epistominella pacifica -0.60 3.22 4
28.5 Epistominella pacifica -0.38 3.47 1
Epistominella pacifica -0.34 3.30 1
Epistominella pacifica -0.29 3.18 1
Epistominella pacifica -0.31 3.27 1
29.5 Epistominella pacifica -0.56 3.23 1
Epistominella pacifica -0.38 3.26 1
Epistominella pacifica -0.22 3.28 1
Epistominella pacifica -0.40 3.02 1