The Impact of Climate Change and Tectonic Events on Ocean Circulation in the Miocene to Pliocene

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Title:
The Impact of Climate Change and Tectonic Events on Ocean Circulation in the Miocene to Pliocene
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english
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Newkirk, Derrick R
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University of Florida
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Degree:
Doctorate ( Ph.D.)
Degree Grantor:
University of Florida
Degree Disciplines:
Geology, Geological Sciences
Committee Chair:
Martin, Ellen E
Committee Members:
Jaeger, John M
Lambeck, Andrea Dutton
Krigbaum, John S
Kamenov, George

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Subjects / Keywords:
amazon -- andes -- carbonate -- cas -- ceara -- circulation -- crash -- lead -- miocene -- neodymium
Geological Sciences -- Dissertations, Academic -- UF
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Geology thesis, Ph.D.
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theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
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Abstract:
cecrLeLNOcTwo major events occurred in the Miocene following the mid-Miocene Climatic Optimum: one was a global cooling trend associated with renewed growth of East Antarctic Ice Sheet, and the other was tectonic closure of the Central American Seaway (CAS). The response of ocean circulation to Antarctic glaciations has been focused in the Southern Ocean and the southwest Pacific, yet little is known about how circulation was affected in the rest of the Pacific, particularly eastern Pacific in the region of the CAS. Shoaling of the CAS in the middle Miocene has been implicated in local and global changes in ocean circulation and climate, and in the development of low carbonate intervals referred to as“carbonate crash” events that are found in the eastern equatorial Pacific, Caribbean, and possibly the western Atlantic. The effects of an open CAS on global thermohaline circulation have also been debated. Several modeling studies have shown that exchange through the CAS would reduce the temperature, and salinity of the water in the north Atlantic, thereby weakening or shutting down North Atlantic Deep Water (NADW) production. Reconstructions of paleocirculation are required to evaluate the impact of closure of this equatorial gateway and high southern latitude climate change. We reconstructed deep water circulation from the early/middle Miocene to the late Pliocene using neodymium (Nd) isotopic records for fossil fish teeth/debris from a longitudinal transect of Ocean Drilling Program sites in the eastern Pacific, two sites in the Caribbean, and a depth transect in the western Atlantic to assess the impact of these events on circulation and carbonate deposition in the Pacific, Caribbean, and Atlantic regions.Nd isotopic records from eastern Pacific sites suggest expansion of Pacific Deep Water (PDW) through the mid to late Miocene, leading to deepening of the boundary between PDW and Circumpolar Deep Water in the eastern equatorial region. This rearrangement of Pacific circulation coincides with increased flow of the Deep Western Boundary Current into the Pacific in response to intensified Antarctic glaciation. Expansion of corrosive PDW into the equatorial Pacific and Caribbean appears to trigger middle Miocene carbonate crash events. Termination of the carbonate crash in the Pacific is attributed to an increase in equatorial surface productivity and carbonate rain rates in this region, while termination of the carbonate crash and a contemporaneous shift from Pacific- to Atlantic-sourced deep water in the Caribbean Basin was associated with shoaling of the CAS. Thus, changes in circulation in the Miocene Pacific appear to be driven by high latitude climate, while changes in the Caribbean are a response to the low latitude tectonic event.Results in the Caribbean highlight the flow of Pacific water through the CAS during times of suggested NADW production, which contradicts many general ocean circulation models that suggest NADW production did not occur with an open CAS. Production estimates of NADW throughout the Miocene are based on Atlantic-Pacific d13C gradients, which are very subtle for this time interval. To better constrain the relative production of NADW and AABW from the middle Miocene to Pliocene, a seawater Nd isotopic record  was developed using samples from Ceara Rise, which is located midway between north and south Atlantic deep water sources and covers a depth range from ~3000-4300 m. The present day position of the boundary between NADW and AABW lies within the depth transect of Ceara Rise. Miocene to Pliocene Nd isotopic records of seawater are far less radiogenic than any known water mass in the Atlantic Ocean, and the record shows a significant shift in values around 8 Ma and a smaller shift at ~4.5 Ma.Evaluation of the silicate fraction of the deep-sea sediments illustrated that the Nd and lead (Pb) isotopic values recovered from fossil fish teeth and ferromanganese oxide coatings on the sediment are very similar to the values of the detrital silicate fractions. The combined detrital silicate and seawater records suggest that extensive detrital inputs in this region overwhelmed the record of seawater isotopes through reversible scavenging, and therefore it was not possible to identify a shift in the boundary between NADW and AABW in the seawater record. On the other hand, the isotopic records were interpreted in terms of changes in source material derived from Amazon lowlands (South American shield material)to material from the Andean highlands (volcanic arc material), indicating a change in the Amazon drainage basin associated with known uplift events of the Andes Mountains. These results show that a transcontinental connection of the Amazon drainage basin occurred at ~8 Ma, and the small shift at ~4.5 was related to continued Andean uplift.
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In the series University of Florida Digital Collections.
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Includes vita.
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This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility:
by Derrick R Newkirk.
Thesis:
Thesis (Ph.D.)--University of Florida, 2012.
Local:
Adviser: Martin, Ellen E.
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RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2013-08-31

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1 THE IMPACT OF CLIMATE CHANGE AND TECTONIC EVENTS ON OCEAN CIRCULATION IN THE MIOCENE TO PLIOCENE By DERRICK RICHARD NEWKIRK A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLME NT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2012

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2 2012 Derrick Richard Newkirk

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3 To my parents Pat and Rick Newki rk, and my brother Nick Newkirk

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4 ACKNOWLEDGMENTS I would like to sincerely thank Dr. El len Martin for her continued guidance on this project. Not only is she a great mentor, but also a good friend and a pleasure to work with Thanks also go to my committee members Dr. Andrea Dutton, Dr. David Hodell, Dr. George Kamenov, Dr. John Jaeg e r, and my external committee member Dr. John Krigbaum. I am also very grateful for the financial support that was provided by the NSF SGR grant awarded to Dr. Ellen Martin, the Department of Geological Sciences, Graduate Student Council, and the College of Liber al Arts and Sciences. Special thanks go to Susanna Blair for her guidance and continuous help in the lab at the beginning of my graduate career and to Dr. Chandranath Basak for the constant entertainment in the lab and great team work Also, I would like to thank Dr. George Kamenov and Dr. Jason Curtis for their assistance in the lab, help with analysis, and suggestions for streamlining laboratory procedures. I would like to also thank the many undergraduates who have helped me in the lab. Finally, I would like to thank my family and friends. Thanks go to Pat and Rick Newkirk for their unfaltering love and support. Thanks go to Ryan Newkirk for being a great friend and a very supportive brother. Thanks go to my girlfriend Emily Pugh for her support and cont inued encouragement to finish the dissertation, and for being a great friend. Thanks go to Scottie Andre for playing a huge role in my upbringing and being a good role model. Thanks go to my many wonderful friends in the Department of Geological Sciences a t UF, especially J onathan Hoffman, Dr. Jason Gulley, Dr. Dorsey Wanless, Dr. Richard MacKenzie, John Ezell, and Dr. PJ Moore Thanks to Dr. Jennifer Latimer for her guidance, friendship, and invaluable lab guidance that she gave me as

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5 an undergraduate rese archer. And last but not least thanks go to all of my wonderful friends outside of the department and from my hometown, especially Jason Wright, Adam Faust, Nick Kaufman, Judd Sparks, Ron Wright, and Carlos Zambrano.

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6 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 8 LIST OF FIGURES ................................ ................................ ................................ .......... 9 ABSTRACT ................................ ................................ ................................ ................... 11 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 14 2 CIRCULATION THROUGH THE CENTRAL AMERICAN SEAWAY DURING THE MIOCENE CARBONATE CRASH ................................ ................................ .. 18 Overview ................................ ................................ ................................ ................. 18 Background ................................ ................................ ................................ ............. 19 Methods ................................ ................................ ................................ .................. 21 Results ................................ ................................ ................................ .................... 22 Discussion ................................ ................................ ................................ .............. 23 Summary ................................ ................................ ................................ ................ 26 3 MIOCENE DEEP WATER CIRCULATION IN THE PACIFIC AND CARIBBEAN: IMPACTS OF THE CENTRAL AMERICAN SEAWAY AND SOUTHERN HEMISPHERE GLACIATION ................................ ................................ ................. 36 Overview ................................ ................................ ................................ ................. 36 Background ................................ ................................ ................................ ............. 39 Modern Pacific Deep Water Circulation ................................ ............................ 39 Shoaling History of the Central American Seaway ................................ ........... 41 Material and Methods ................................ ................................ ............................. 42 Core Descriptions and Age Model ................................ ................................ .... 42 S ample Preparation and Nd Isotope Measurements ................................ ........ 43 13 C Sample Preparation and Measurements ................................ .................. 44 Results ................................ ................................ ................................ .................... 44 Discussion ................................ ................................ ................................ .............. 45 Circulation in the Eastern Pacific ................................ ................................ ...... 45 The m iddle to l ate Miocene t ransitio n (14 9 Ma) ................................ ..... 45 Late Mioce ne to Pliocene (8.5 to 2.5 Ma) c irculation ................................ 50 History of the Caribbean Basin ................................ ................................ ......... 52 Summary ................................ ................................ ................................ ................ 55

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7 4 TRANSCONTINENTAL CONNECTION OF THE AMAZON RIVER BASED ON CEARA RISE SEAWATER RECORDS ................................ ................................ .. 76 Overview ................................ ................................ ................................ ................. 76 Material and Methods ................................ ................................ ............................. 80 Results ................................ ................................ ................................ .................... 82 Dis cussion ................................ ................................ ................................ .............. 83 The Seawater Signature ................................ ................................ ................... 83 Interpretation of Detrital Isotopes ................................ ................................ ..... 87 Summary ................................ ................................ ................................ ................ 90 5 CONCLUSIONS ................................ ................................ ................................ ... 105 LIST OF REFERENCES ................................ ................................ ............................. 107 BI OGRAPHICAL SKETCH ................................ ................................ .......................... 122

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8 LIST OF TABLES Table page 2 1 Nd isotopic values for modern and Miocene water masses ................................ 31 2 2 Nd isotopic results for Sites 846B, 998A, 999A, and 1241A ............................... 32 3 1 Nd isotopic results for the Pacific (Sites 845, 846, 1237, and 1241) ................... 67 3 2 Nd isotopic results for the Caribbean Basin (Sites 998A and 999A) ................... 72 4 1 Nd isotopic results for Ceara Rise fossil fish teeth ................................ .............. 98 4 2 Nd isotopic values for detrital silicates ................................ .............................. 102 4 3 Pb isotopic values for detrital silicates ................................ .............................. 103 4 4 Pb isotopic values for leachates ................................ ................................ ....... 104

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9 LIST OF FIGURES Figure page 2 1 Plate reconstruction of the Caribbean region at 10 Ma. ................................ ...... 27 2 2 Carbonate MARs and Nd values from Site 846 Site 998 Site 999. ................... 28 2 3 Nd isotopic data for Sites 998 and 999 in the Caribbean Basin, Sites 846 and 1241 in the eastern equatorial Pacific. ................................ ................................ 29 2 4 Nd values for Site 998 plotted with %NCW. .................... 30 3 1 Bathymetric map of the Pacific Basin and Caribbean Basin illustrating the different basins of the eastern P acific and the associated sills controlling the flow of deep water. ................................ ................................ ............................. 57 3 2 Map of the Pacific Ocean illustr ating the flow paths ................................ .......... 58 3 3 North South Seawater profile for the central Pacific determined using the phosphate concentration profile for the mode rn Pacific ocean .......................... 59 3 4 Seawater Nd isotopic values for the deep w ater sites (845, 846, and 1237) of the eastern Pacific compared to published values for the central Pacific and the north Pacific. ................................ ................................ ................................ 60 3 5 Nd isotopic values for the eastern Pacific vesus the c arbon record. ................... 61 3 6 Seawater Nd isotopic data for Ocean Drilling Program Sites 998 and 999 in the Caribbean Basin Compared to the published values (shaded fields) for the Pacific. ................................ ................................ ................................ .......... 62 3 7 Changes in the Nd isotopic composition of water masses from the beginning of the record to 9 Ma from the central equatorial Pacific the north Pacific and the three eastern Pacific sites from th is study. ................................ ............ 63 3 8 North South Seawater profiles for the central Pacific showing the shifts in the boundaries between P acific water mass ................................ ........................... 64 3 9 North South Seawater profiles for the eastern Pacific Pacific showing the shifts in the boundaries between Pacific water mass. ................................ ........ 65 3 10 Seawater Nd isotopic data for the eastern Pacific, the Caribbean Basin, and th e Straits of Florida near Blake Nose. ................................ ............................... 66 4 1 Bathym etric map of the Atlantic Ocean and the bathymetric profile illustrating the position of Ocean Drill ing Program sites 925, 926, 929 ............................... 92

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10 4 2 Salinity profile along a north south transect in the Atlantic overlain by Nd profiles. ................................ ................................ .......................... 93 4 3 Nd from fossil fish teeth vs. age for sites 925, 926, and 929 on Ceara Rise in the western equatorial Atlantic. ................................ ............................... 94 4 4 Nd vs. age for detrital silicate fractions and foss il fish teeth for sites 925, 926, and 929 on Ceara Rise. ................................ ................................ ...................... 95 4 5 206 Pb/ 204 Pb vs. age for both detrital silicate fractions and Fe Mn oxide coatings for sites 925, 926, and 929 on Ceara Rise. ................................ .......... 96 4 6 Pb isotopic crossplots of the detrital silicate fractions from all three Ceara Rise sites (925, 926, and 929). ................................ ................................ ........... 97

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11 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy THE IMPACT OF CLIMATE CHANGE AND TECTONIC EVENTS ON OCEAN CIRCULATION IN THE MIOCENE TO PLIOCENE By Derrick Richard Newkirk August 2012 Chair: Ellen E. Martin Major: Geology Two major events occurred in the Miocene following the m id Miocene Climatic Optimum: one was a global cooling trend associated with renewed growth of East Antarctic Ice Sheet, and the ot her was tectonic closure of the Central American Seaway (CAS). The response of ocean circulation to Antarctic glaciations has been focused in the Southern Ocean and the southwest Pacific, yet little is known about how circulation was affected in the rest o f the Pacific, particularly eastern Pacific in the region of the CAS. S hoaling of the CAS in the m iddle Miocene has been implicated in local and global changes in ocean circulation and climate, and in the development of low carbonate intervals referred to that are found in the eastern equatorial Pacific, Caribbean, and possibly the western Atlantic. The effects of an open CAS on global thermohaline circulation have also been debated. Several modeling studies have shown that excha nge through the CAS would reduce the temperature, and salinity of the water in the north Atlantic, thereby weakening or shutting down North Atlantic Deep Water (NADW) production Reconstructions of paleo circulation are required to evaluate the impact of cl osure of this equatorial gateway and high southern latitude climate change

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12 W e reconstructed deep water cir culation from the early/middle M iocene to the late Pliocene using neodymium (Nd) isotopic records for fossil fish teeth/debris from a longitudinal t ransect of Ocean Drilling Program sites in the eastern Pacific two sites in the Caribbean and a depth transect in the western Atlantic t o assess the impact of these events on circulation and carbonat e deposition in the Pacific, Caribbean and Atlantic re gions Nd isotopic records from eastern Pacific sites suggest expansion of Pacific Deep Water (PDW) through the mid to late Miocene, leading to deepening of the boundary between PDW and Circumpolar Deep Water in the eastern equatorial region. This rearrang ement of Pacific circulation coincides with increased flow of the Deep Western Boundary Current into the Pacific in response to intensified Antarctic glaciation. Expansion of corrosive PDW into the equatorial Pacific and Caribbean appears to trigger middle Miocene carbonate crash events. T ermination of the carbonate crash in the Pacific is attributed to a n increase in equatorial surface productivity and carbonate rain rates in this region, while termination of the carbonate crash and a contemporaneous shift from Pacific to Atlantic sourced deepwater in the Caribbean Basin was associated with shoaling of the CAS. Thus, changes in circulation in the Miocene Pacific appear to be driven by high latitude climate, while changes in the Caribbean are a response to the low latitude tectonic event. Results in the Caribbean highlight the flow of Pacific water through the CAS during times of suggested NADW production which contradicts many general ocean circulation models that suggest NADW production did not occu r with an open CAS P roduction estimates of NADW throughout the Miocene are based on Atlantic Pacific 13 C gradients, which are very subtle for this time interval To better constrain the

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13 relative production of NADW and AABW from the middle Miocene to Pliocene, a seawater Nd isotopic record was developed using samples from Ceara Rise, which is located midway between n orth and s outh Atlantic deep water sources and covers a depth range from ~3000 4300 m The present day position of the boundary between NADW and AABW lies within the depth transect of Ceara Rise. Miocene to Pliocene N d isotopic records of seawater are far less radiogenic than any known water mass in the Atlantic Ocean, and the record show s a significant shift in values around 8 Ma and a smaller shift at ~4.5 Ma Evaluation of th e silicate fraction of the deep sea sedim ents illustrated that the Nd and lead (Pb) isotopic values recovered from fossil fish teeth and ferromanganese oxide coatings on the sediment are very similar to the values of the detrital silicate fraction s. The combined detrital silicate and seawater rec ords suggest that extensive detrital inputs in this region overwhelm ed the record of seawater isotopes through reversible scavenging, and therefore it was no t possible to identify a shift in the boundary between NADW and AABW in the seawater record On the other hand, t he isotopic records were interpreted in terms of changes in source material derived from Amazon lowlands (South American shield material) to material from the Andean highlands (volcanic arc material), indicating a change in the Amazon drainag e basin as sociated with known uplift events of the Andes Mountains. These results show that a transcontinental connection of the Amazon drainage basin occurred at ~8 Ma and the small shift at ~4.5 was related to continued Andean uplift.

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14 CHAPTER 1 INTR ODUCTION R econstruction of deep water circulation allows for a more thorough evaluation of the relationship between changes in ocean circulation and climate. One of the big questions paleoceanographers and paleoclimatologists are trying to address is the r ole ocean circulation plays in driving climate, such as the onset of glaciations, as well as impact climate has on circulation. Tectonic gateway events have long been suggested to play a significant role in altering ocean circulation and producing conditio ns conducive to onset of glaciations in both hemispheres. The focus of this study revolves around understanding the relationship of the shoaling of the Central American Seaway to suggested changes in regional (eastern equatorial Pacific and Caribbean) and global ocean circulation and ultimately how those changes have affected climate change and deep sea sedimentation patterns, particularly with reference to low carbonate accumulation intervals referred Neodymium (Nd) isotopes recovered from fossil fish teeth were used to reconstruct circulation in the eastern Pacific, Caribbean, and western equatorial Atlantic to determine how gateway events and climate change altered circulation in these regions Nd isotopes were chosen becau se they are considered to be quasi conservative tracers of water mass, meaning that the cores of different water masses have distinct Nd isotopic signatures that can only be altered through water mass mixing or addition of local weathering inputs [ Frank 2 002; Goldstein and Hemming 2003]. Important for this proxy is the fact that the residence time of Nd in the oceans [~600 1000 yrs; Elderfield and Greaves 1982; Piepgras and Wasserburg 1985; Jeandel et al. 1995; Tachikawa et al. 1999; Arsouze et al. 2009] is shorter than the modern

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15 ocean mixing time of ~1500 years [ Broecker and Peng 1982]. Fossil fish teeth and debris have been demonstrated to be robust paleoceanographic archives of bottom water Nd isotopes [ Elderfield and Pagett 1986; Martin and H aley 2000; Thomas et al. 2003; Martin and Scher 2004; Thomas 2004; Scher and Martin 2006]. During the m iddle Miocene the eastern equatorial Pacific [ Vincent, 1981 ; Mayer et al., 1986 ; Farrell et al., 1995 ; Lyle et al., 1995], and Caribbean [ Roth et a l., 2000 ] recorded events [ Lyle et al., 1995]. Lyle et al. [1995] and Roth et al. [2000] suggested observed carbonate crash events in both the Pacific and Caribbean were related to changes in circulation coinciding with shoaling of the Central American Seaway (CAS) in the Middle Miocene but they could not determine how circulation changed Chapter 2 attempts to understand how circulation changed in the Caribbean and determine whe ther carbonate dissolution was the result of an influx of corrosive Antarctic Intermediate Water (AAI W) sourced from the Atlantic or corrosive water sourced from the north Pacific. Chapter 2 was published in the journal title d Geology in January of 2009 [ N ewkirk and Martin 2009]. The primary goal of Chapter 3 was to reconstruct deep water circulation in the eastern Pacific and Caribbean during the Miocene using Nd isotopic records for fossil fish teeth/debris from a longitudinal transec t of four Ocean Dril ling Program (ODP) sites in the eastern Pacific (Site 845, 846, 1231, and 1241) and expanded datasets for Caribbean records (ODP sites 998 and 999) to improve our understanding of processes driving circulation in the Pacif ic and Caribbean following the m id Miocene Climatic Optima and shoaling CAS on conditions in the Caribbean Basin

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16 Ge neral ocean circulation models suggest NADW production should not occur with an open CAS ; however, Nd isotopic r esults from Chapters 2 and 3 [ Newkirk and Martin, 2009] ind icate the strongest fluxes of Pacific water into the Caribbean during times of purported strong NADW production Chapter 4 attempts to evaluate shifts in the boundary between Northern Component Water (NCW) and Antarctic Bottom Water ( AABW ) which has been shown to shoal and deepen depending on relative production rates of these water masses. To investigate variations in NCW and AABW we analyzed Nd isotopes of fossil fish teeth from a depth transect spanning from ~3000 4300 m on Ceara Rise that included ODP sites 925, 926, and 929. The goals was to use v ariations in the Nd isotopic r ecords of these sites to establish the position of th e NCW/AABW interface through time and determine if a direct correlation exist ed between carbonate dissolution and the influx o f AABW over the Ceara Rise. Our e arly results of seawater Nd isotopes indicated the values were strongly influenced by a signal from Amazon sediments. Thus, the study was refocused to understand the impact of a major river outflow on the seawater Nd isoto pes preserved in fish teeth and to evaluate changes to the composition of terrigenous material weathered from South America which improved our understanding of the evolution of the Amazon River basin and the impact of the extensive sediment supply on the seawater Nd isotopic signal. Depending on the location of the study (inland, proximal fan, distal Amazon outflow) and the proxy applied, different studies have come to different conclusions about the outlet for the Amazon River (Caribbean versus Atlantic), and the timing and cause of shifts in the composition of material carried by the river.

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17 To further evaluate suggested changes in provenances of material reaching the Ceara Rise [ Harris and Mix 2002 ; Dobson et al. 2001] and constrain the timing of the shift in provenance, detrital silicate fractions were separated from bulk sediment samples from all three sites (925, 926, 929) and analyzed for Nd and lead ( Pb ) The Nd and Pb isotopic data help to better constrain the timing of a shift from a system domi nated by South American Shield material to one dominated by Andean material, and also to determine whether the shift at ~4.5 Ma in the clay mineralogy identified by Harris and Mix [2002] was the result of continued Andean uplift or changes in weathering re lated to changing climatic conditions.

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18 CHAPTER 2 CIRCULATION THROUGH THE CENTRAL AMERICAN SEAWAY DURING THE MIOCENE CARBONATE CR ASH Overview The Caribbean carbonate crash, an interval of low carbonate mass accumulation rates (MARs) in the middle to late M iocene, has been linked to the presence of corrosive waters in the Caribbean associated with changes in circulation patterns and shoaling of the Isthmus of Panama. For example, Roth et al. [ 2000 ] suggested that North Atlantic Intermediate Water (NAIW) flow ed over shallow to intermediate depth sills on the Atlantic side of the Caribbean Basin during times of enhanced carbonate preservation, while corrosive Antarctic Intermediate Water (AAIW) overflowed the sills during intervals of carbonate dissolution. Thi s configuration was based on the correlation between carbonate crash intervals and periods of more intense Northern Component Water (NCW) production defined by Wright and Miller [ 1996 ] as well as modern circulat ion of AAIW into the Caribbean [ Haddad and D roxler 1996 ] In contrast, several general circulation models (GCMs) with an open Central American Seaway predict west to east flow at depth through the gateway, such that some of the waters flowing into the Caribbean would have been derived from the Paci fic [ Mikolajewicz and Crowley 1997; Nisancioglu et al. 2003; Prange and Schulz 2004; Schneider and Schmittner 2006; Steph et al. 2006 ] Traditional paleoproxy data from this region cannot distinguish between South Atlantic and Pacific sources of cor rosive waters. In contrast, neodymium (Nd) isotopic compositions of these water masses are highly distinct. The Nd isotopic signature of seawater is considered to be a conse rvative tracer of water masses [ Goldstein and Hemming 2003 and references therein ] End member Nd isotopic compositions for

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19 Miocene water masses potentially flowing into the Caribbean are well constrained by published data from Fe Mn crusts and fish teeth, and data in this paper (Table 2 1 ). Fossil fish teeth and debris composed of hydr oxyfluorapatite have been demonstrated to be robust paleoceanographic archiv es of bottom water Nd isotopes [ Martin and Scher 2004 and references therein ] making them powerful archives during the Caribbean carbonate crash. In this paper we report Nd iso topic values for fossil fish teeth and debris from Ocean Drilling Program Sites 998 and 999 in the Caribbean and Sites 846 and 1241 in the eastern equatorial Pacific (Fig ure 2 1 and 2 2) in order to identify sources of bottom waters and basic circulation p atterns in the Caribbean during closure of the Central American Seaway and the Miocene Caribbean carbonate crash. The two Caribbean sites are ideally located to correlate regional changes in circulation to large scale changes in the thermohaline circulatio n defined by variations in NCW, or proto North Atlantic Deep Water, production. Background The water masses filling the Caribbean have changed as sills on the eastern and western margins of the basin evolved. On the Atlantic side, the Windward Passage (150 0 m) and the Anegada Jungfern Passage (1800 m) are pathways for intermediate waters to enter the basin (Fig ure 2 1). On the Pacific side, the Isthmus of Panama currently blocks all inflow into the Caribbean, but an open Central American Seaway would have a llowed exchange between these basins during the Miocene until final closure in the Pliocene. Specifically, the Isthmus of Panama is believed to have shoaled to ~1000 m between 12 10.2 Ma based on ben thic foraminiferal assemblages [ Duque

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20 Caro 1990] while final closure has bee n placed between ~4.2 2.4 Ma [ Keller et al. 1989; Haug et al. 2001] Due to its short oceanic residence time and predominant continental sources, different water masses have distinct Nd isotopic ratios that reflect the geology of source regions. Miocene North Atlantic, South Atlantic, and Pacific water masses have distinct Nd values (Table 2 1 ) enabling the reconstruction of changing circulation patterns in response to shoaling of the Isthmus of Panama. Site 998 is located in th e Yucatan Basin at a modern water depth of 3180 m and Site 999 is located in the Columbian Basin at a modern water depth of 2828 m (Figure 2 1). Although both sites are relatively deep, bottom waters in the Caribbean are derived from intermediate to shallo w waters overflowing sills separating the Caribbean from the Pacific and Atlantic. Thus, sill depths of these passageways rather than paleodepths for the specific sites control the composition of bottom waters in the basin. The end member composition of wa ter on the Pacific side of the Central American Seaway was determined using data from two sites in the eastern equatorial Pacific; Site 846 in the Peru Basin (3296 m modern water depth) and Site 1241 on the Cocos Ridge (2027 m modern water depth). Lyle et al. [1995] calculated that Site 846 subsided ~50 m between 10 Ma and today. Subsidence of several hundred meters proposed for Site 1241 [ Mix et al. 2003] would place it at an ideal depth to monitor intermediate waters flowing through the Central American Seaway during the Miocene. Age depth models for all four sites are based on the same biostratigraphic boundaries and age datums defined by Raffi and Flores [1995] at Site 846 and applied to Sites 998 and 999 by Kameo and Bralower [2000] and to Site 1241 b y Mix et al. [2003]

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21 Methods Sediment samples were oven dried, disaggregated and wet sieved prior to pickin cleaned using an oxidative/reductive cleaning technique from Boyle [1981] and Boyle and Keigwin [1985] that removes organic matter and Fe Mn oxide coatings. Concentrations of Nd in teeth typic ally range from 100 to 400 ppm [ Martin and Haley 2000] thus ~100 g of cleaned teeth were processed in order to produce at least 10 ng Nd for analysis. Cleaned teeth were dissolved in aqua regia and then dried prior to a two step chemic al separation to isolate Nd. Bulk rare earth elements (REEs) were separated from the sample on a primary quartz column that uses Mitsubishi cation exchange resin with HCl as the eluent [Scher and Martin, 2004] Nd was further isolated using quartz columns packed with Teflon beads coated with bis ethylhexyl phosphoric acid and HCl as the eluent. The total blank for this technique is 14 pg Nd. Nd isotopic ratios were measured on a Nu Plasma Multi Collector Inductively Coupled Plasma Mass Spectrometer (MC IC P MS) at the University of Florida. Dried samples were re dissolved with 0.3 ml of 2% O ptima HNO 3 and then a portion of the sample was pipetted into a Teflon sampling beaker and diluted 100 times using 2% O ptima HNO 3 Additional acid or sample was then added as needed to achieve the ideal voltage of 2 6 volts for 143 Nd. Belshaw et al. [1998] describe the instrument and the optimal operating conditions for the Nu MC ICP MS. JNdi 1 standard was run between every 4 to 6 samples, depending on the number o f analyses acquired. All of the JNdi 1 values analyzed during one day were averaged and that value was normalized to the long term TIMS value of 0.512103

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22 sample runs were then normalized by the same amount to correct for the daily variations in running conditions. A drift correction was not applied because variations ror for the Nu MC ICP MS based on the variability of normalized JNdi 1 analyses is 0.000015, which is equivalent Nd units and agrees well with data from replicate analyses (Table 2 2), which Nd units with an average differenc Nd units. Concentrations of Sm and Nd were analyzed on an Element II for three samples from each site in order to determine 147 Sm/ 144 Nd ratios. The average 147 Sm/ 144 Nd ratios are 0.120 for Site 846, 0.134 for Site 998, 0.135 for Site 999, and 0,127 for Site 1241. These ratios were then used to correct for age dependent ingrowth of radiogenic 143 Nd Nd(T) ) Nd units) for these young samples. Results The records for Caribbean Sites 998 and 999 are divid ed into pre crash (~ 14 to 12 Ma), crash (12 10 Ma), and post crash intervals based on carbonate MAR records from Roth et al. [2000] (Figure 2 Nd values at both sites show distinct values and patterns associated with these three intervals (Table 2 2) The pre crash intervals Nd values of approximately 4 and 3 respectively. The beginning of the pre Nd values that increase from 5.5 to 3, while carbona te MARs decrease. The transition into the crash is marked by a divergence of Nd isotopic values with values increasing to ~0 at Site 998 and decreasing to ~ 6.5 at Site 999. However, during the remainder of Nd values exhibit greater va riability, ranging between 4.5 and 0, and the two sites illustrate more similar patterns with a general correlation between low Nd values. During the post Nd values

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23 ultimately decrease to values < 6 at both sites; although, Site 999 records a brief increase to ~ 2 before decreasing abruptly to ~ 6.5, while Site 998 records a gradual decreasing trend. At Site 846 low carbonate MARs representing a distinct eastern equatorial Pacific carbonate crash are younger than t hose of the Caribbean carbonate crash interval. The Pacific record has been divided into pre crash and crash intervals. During the pre crash from 14.1 to 11.2 Ma, carbonate MARs are ~0.5 to 1.0, while Nd value s trend from 3.8 to ~ 2.5 (Figure 2 2 ; Table 2 2 ). During the crash interval from 11.2 to 8 Ma, carbonate Nd values remain relatively stable, ranging between ~ 1.7 and 2.9. As with the Caribbean sites, the cras h interval at Site 846 is characterized Nd values. No carbonate MAR data are available Nd values at this site are even more radiogenic than Site 846, with values ranging between 3 and +2 from 11.3 to 5 Ma (Figure 2 3). Discussion Nd values within the Caribbean extend to values that are higher than any known intermediate or deep wa ter mass from the Atlantic (Figure 2 3). These radiogenic values could represent water sourced from another regio n or alteration of the seawater signal by material introduced into the water column or sediment. Abundant Nd values up to +9 [ Feigenson et al. 2003] represents an obvious potential source of radiogenic material in the Caribbean; however there is no Nd values and volcanic ash MARs at Sites 998 and 999. Instead, Nd values during the crash at Sites 998 and 999 are similar to the most radiogenic seawater values recorded in the Pacific today and during the Mioc ene (F igure 2 3).

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24 Pacific Nd Nd values and lower carbonate MARs in the Caribbean are consistent with the idea that corrosive, radiogenic upper deep/intermediate Pacific waters filled the basin during i ntervals of dissolution, with a greater influx of less corrosive, less radiogenic upper deep/intermediate Atlantic waters during intervals of enhanced preservation. In Nd values during the crash are similar to values recorded at Site 1241, whi ch represents intermediate waters at the proper depth to flow into the Caribbean. Minor differences between records at Sites 998 and 999 can be attributed to the prese nce of the Nicaraguan Rise (Figure 2 1), which separated the north and south Caribbean un til ~12 Ma when faulting initiated a north south oriented pass ageway for intermediate waters [ Droxler et al. 1998; Roth et al. 2000] Before and after the Caribbean carbonate crash, Nd values exceed value s recorded in the Atlantic (Figure 2 3), indicating that Pacific throughflow dominated the deep Caribbean throughout our record, although it was diluted by Atlantic throughflow during intervals of enhanced preservation. Thi s dominance of Pacific throughflow when the Central American Seaway was open to at least ~1000 m is also predicted by several GCMs [ e.g., Mikolajewicz and Crowley 1997; Nisancioglu et al. 2003; Prange and Schulz 2004; Schneider and Schmittner 2006; Ste ph et al. 2006; Lunt et al. 2007 ] As the Central American Seaway continued to shoal, post crash data within the Caribbean Nd values, indicating increased input of Atlantic water. This change in source input as a result of the shoaling of the Central American Seaway is consistent with the idea proposed by Frank et al. [ 1999] and Reynolds et al. [1999] Nd

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25 values they reported for an Fe Mn crust from the Florida Straits, which sampled water leaving the Caribbean (Fig ure 2 3). Their data only extend to 8.5 Ma, but data from Sites 998 and 999 pinpoint the initiation of decreased throughflow at ~10.7 Ma. Flow of Pacific water into the Caribbean is also supported by data on coccolith and planktonic foraminiferal assemblages at this time. Nannofossil assemblages at Site 999 are similar to assemblages re ported in the eastern equatorial Pacific from 15.9 10.7 Ma. They begin diverging from Pacific type assemblages between 13.6 10.7 Ma, and became completel y distinct between 10.7 9.4 Ma [ Kameo and Sato 2000] In addition, [2000] attribu ted temperate latitude foraminiferal assemblages ( Globoconellids ) observed at Site 999 until ~10.7 Ma to an influx of cool Pacific surface water from either the California or Peru Currents. Nd values do not correspond to Nd values at Site 998 increase dramatically, while values at Site 999 decrease to a value be low the Pacific end member (Figure 2 3). This less radiogenic value co uld represent a mixture of two relatively corrosive water masses, North Pacific Intermed iate Water (NPIW) and AAIW (Figure 2 3), while the more radiogenic values observed at Site 998 may indicate that only the shallowest, Pacific derived waters could cross the Nicaraguan Rise. The second deviation occurs at the beginning of the post crash interval at Site 999. The observed Nd values and enhanced carbonate preservation suggests this water could represent a mixture of radiogenic upper NPIW and non corrosive NAIW, or a system dominated by nutrient rich Pacific waters leading to enhanced carbonate rain rates and preservation.

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26 Nd at Site 998 compar ed to estimated NCW production [ Wright and Miller 1996; Poore et al. 2006] suggests a correlation between enhanced production of NCW and increased Pacific throughflow from ~12.4 to 9.5 Ma (Fig ure 2 4). This relationship suggests that flow patterns in the Caribbean region were linked to global circulation and that northward flow of low salinity waters due to strong equatorial exchange did not limit NCW production. Nisancioglu et a l. [2003] present the only GCM to predict significant NCW production with an open Central American Seaway and geostrophic flow from the Pacific to the Atlantic. Summary Nd isotopes from fossil fish teeth and debris at Sites 998 and 999 in the Caribbean and Sites 846 and 1241 in the eastern equatorial Pacific indicate that waters sourced from the Pacific dominated flow into the Caribbean during the Miocene Caribbean carbonate crash. Prior to the Caribbean crash a gradual decrease in carbonate MARs and an ass o Nd values at Site 999 provide evidence for the introduction of a more corrosive, Pacific intermediate water mass into the Caribbean as the Central American Seaway shoaled to critical depths for west to east flow. During the Caribbean ca rbonate crash (12 Nd values and carbonate MARs record pulses of almost pure, corrosive Pacific waters that filled the deep Caribbean. These pulses of Pacific throughflow correlate well with NCW production, suggesting that NCW produc tion can occur with an open Central American Seaway and that flow patterns in the Caribbean region are linked to global circulation patterns. After the Nd values gradually shift to less radiogenic values indicating a reduction in the amount of Pacific water flowing into the Caribbean coincident with the shoaling of the Isthmus of Panama.

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27 Figure 2 1. Plate reconstruction of the Caribbean region at 10 Ma [ after Pindell 1994] illustrating locations of geographic features, as well as ODP sites used in this study (Sites 846, 998, 999, and 1241) and one Fe Mn crust (BM1963.897) from Reynolds et al. [1999]

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28 Figure 2 2. Carbonate MARs (small filled circles for all sites) and Nd values from (A) Site 846 (diamonds) in the eastern equatorial Pacific, (B) Site 998 (large circles), and (C) Site 999 (squares) in the Caribbean Basin. Note the Nd scale is slightly different for Site 846. Carbonate MARs are from Farrell et al. [1995] for Site 846 and Roth et al. [2000] for Sites 998 and 999. The carbonate crash interval highlighted in gray is defined by variable, but low carbonate MARs.

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29 Figure 2 3 Nd isotopic data for Sites 998 and 999 in the Caribbean Basin, Sites 846 and 1241 i n the eastern equatorial Pacific, and data by Reynolds et al. [ 1999 ] for crust BM1963.897 from the Straits of Florida. Shaded fields represent the range of Nd values from the South Atlantic [ Thomas and Via 2007] North Atlantic [ Burton et al. 1997, 1999; 1998; Reynolds et al 1999], North Pacific [ van de Flierdt et al. 2004] and central equatorial Pacific [ Ling et al. 1997; Frank et al. 1999] No data older than 12 Ma are available for North Pacific intermediate /deep waters.

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30 Figure 2 4 Ca rbonate MARs (thin black line) [ Roth et al. Nd values (filled circles and thick black line) for Site 998 plotted with %NCW (thick gray line) from Wright and Miller [1996] The %NCW was calculated using interbasin gradients in 13 C. There are large age uncertainties within the compiled data. In addition, low 13 C gradients after 12 Ma translate to large uncertainties i n NCW production in the older portion of the record.

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31 Table 2 1. Nd isotopic values for modern and Miocene water masses Water Mass Nd Nd AAIW 7 to 9 (4) 8 (10, 11) AABW 8 to 9 (4) 8 (10) UNADW/NAIW 13 (2) 11 (5, 8) NADW 13.5 (2) 11.5 (7) PDW 4 (3) 4 (6, 9) EEPDW* 3.8 (3) 3.6 to 1.6 (10, 13) NPUDW # /NPIW 3 (3) 2.5 to 1.5 (12) Equatorial PIW 0 (1) +2 to 0.6 (13) 1 Piepgras and Wasserburg 1982; 2 Piepgras and Wasserburg 1987; 3 Piepgras and Jacobsen 1988; 4 Jeandel 1993; 5 Burton et al. 1997; 6 Ling et al. 1997; 7 1998; 8 Burton et al. 1999; 9 Martin and Haley 1999; 10 Frank et al. 1999; 11 Scher and Martin 2004; 12 van de Flierdt et al. 2004; 13 this study EEPDW = Ea stern Equatorial Pacific Deep Water # NPUDW = North Pacific Upper Deep Water.

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32 Table 2 2 Nd isotopic results for Sites 846B, 998A, 999A, and 1241A Site Depth (mbsf) Age (Ma) a 143 Nd/ 144 Nd b Nd(o) c Nd(t) d 846B 29X 6W 61 67 272.3 4 8.09 0.512488 2.9 2.9 846B 30X 3W 110 116 278.03 8.43 0.512549 1.7 1.7 846B 31X 1W 77 83 284.30 8.81 0.512547 1.8 1.7 846B 31X 2W 101 107 286.04 8.92 0.512523 2.2 2.2 846B 31X 4W 98 104 289.02 9.10 0.512535 2.0 1.9 846B 31X 6W 101 107 292. 04 9.29 0.512522 2.3 2.2 292.04 9.29 0.512536 2.0 1.9 846B 32X 4W 103 109 298.66 9.69 0.512523 2.2 2.1 298.66 9.69 0.512545 1.81 1.8 846B 32X 6W 27 33 300.90 9.82 0.512526 2.2 2.1 300.90 9.82 0.512534 2.0 1.9 846B 32X 6W 94 100 301.57 9.86 0.512532 2.1 2.0 846B 33X 1W 100 107 303.84 10.00 0.512554 1.6 1.5 846B 33X 2W 31 37 304.64 10.05 0.512526 2.2 2.1 846B 33X 4W 144 150 308.78 10.30 0.512527 2.2 2.1 846B 33X 6W 30 36 310.63 10.42 0.512510 2.5 2.4 846B 34X 1W 140 146 313 .83 10.61 0.512488 2.9 2.8 846B 34X 3W 121 127 316.64 10.78 0.512519 2.3 2.2 316.64 10.78 0.512534 2.0 1.9 846B 34X 4W 111 117 318.04 10.87 0.512531 2.1 2.0 318.04 10.87 0.512512 2.5 2.4 846B 34X 7W 21 27 321.64 11.09 0.512541 1.9 1.8 8 46B 36X 2W 128 134 334.51 11.87 0.512500 2.7 2.6 334.51 11.87 0.512482 3.0 2.9 846B 36X 3W 128 134 336.01 11.96 0.512481 3.1 3.0 846B 37X 2W 93 99 343.76 12.43 0.512519 2.3 2.2 343.76 12.43 0.512520 2.3 2.2 846B 38X 4W 144 150 356.98 13.23 0.512490 2.9 2.8 846B 40X 1W 121 127 371.54 14.14 0.512446 3.7 3.6 998A 10H 2W 45 50 86.78 4.50 0.512260 7.4 7.3 998A 11H 6W 129 134 103.12 5.50 0.512286 6.9 6.8 998A 12H 6W 58 63 111.91 6.50 0.512312 6.4 6.3 998A 13H 4W 66 71 118.4 9 7.25 0.512306 6.5 6.4 998A 14H 1W 6 11 122.88 7.75 0.512451 3.7 3.6 998A 14H 3W 145 150 127.28 8.25 0.512323 6.2 6.1 998A 14H 3W 64 69 129.47 8.50 0.512349 5.6 5.6 998A 15H 1W 21 26 132.51 8.95 0.512300 6.6 6.5 998A 15H 3W 107 113 136.37 9 .33 0.512323 6.2 6.1 998A 15H 5W 27 32 138.58 9.52 0.512333 6.0 5.9 138.58 9.52 0.512314 6.3 6.2 998A 16H 1W 54 59 141.85 9.79 0.512379 5.1 5.0 998A 16H 3W 126 129 146.05 10.14 0.512351 5.6 5.5

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33 Table 2 2. Continued Site Depth (mbsf) Age (Ma) a 143 Nd/ 144 Nd b Nd(o) c Nd(t) d 998A 16H 4W 32 37 146.62 10.18 0.512396 4.7 4.6 146.62 10.18 0.512416 4.5 4.45 998A 16H 4W 45 50 146.77 10.19 0.512457 3.5 3.5 998A 16H 5W 25.5 30 148.11 10.30 0.512378 5.1 5.0 998A 16H 6W 32 36 149.65 10.46 0.512400 4.7 4.6 998A 16H 6W 125 130 150.58 10.59 0.512491 2.9 2.8 998A 17H 1W 21 26 151.53 10.73 0.512496 2.8 2.7 998A 17H 1W 32 37 151.62 10.75 0.512545 1.8 1.7 998A 17H 1W 77 82 152.08 10.82 0.512498 2.7 2.7 998A 17H 1W 10 5 110 152.35 10.86 0.512466 3.4 3.3 998A 17H 2W 25 30 153.05 10.97 0.512440 3.9 3.8 998A 17H 2W 54 60 153.36 11.02 0.512476 3.2 3.1 998A 17H 2W 126 131 154.06 11.13 0.512438 3.9 3.8 154.06 11.13 0.512431 4.1 4.0 998A 17H 4W 55 60 156.38 11. 50 0.512574 1.3 1.2 998A 17H 5W 2 7 157.38 11.66 0.512440 3.9 3.8 998A 17H 5W 134 139 158.68 11.82 0.512491 2.9 2.8 998A 17H 6W 26 31 159.09 11.87 0.512637 0.0 0.06 998A 17H 6W 81 87 159.65 11.93 0.512594 0.9 0.8 998A 17H CCW 2 7 160.62 12.03 0.512626 0.2 0.2 998A18X 1W 105 111 161.85 12.17 0.512420 4.3 4.2 998A 18X 3W 32 36 164.12 12.41 0.512457 3.5 3.4 998A 19X 1W 53 58 166.75 12.70 0.512418 4.3 4.2 998A 19X 5W 24 28 172.44 13.50 0.512445 3.8 3.7 998A 20X 2W 32 36 177.72 14.05 0.512434 4.0 3.9 998A 22X 3W 21 26 198.34 16.00 0.512435 4.0 3.8 998A 24X 2W 145 150 217.38 17.00 0.512420 4.3 4.1 998A 25X 3W 76 81 227.79 17.50 0.512399 4.7 4.5 998A 26X 4W 7 12 238.20 18.00 0.512514 2.4 2.3 999A 17X 5W 42 47 156.5 5 5.0 0.512301 6.57 6.54 999A 18X 6W 90 95 168.03 5.5 0.512316 6.09 6.04 999A 19X 4W 14 19 173.77 5.75 0.512338 5.85 5.81 999A 20X 1W 88 93 179.51 6.00 0.512309 6.42 6.37 999A 23X 2W 34 39 202.47 7.00 0.512291 6.77 6.72 999A 23X 6W 8 13 208. 21 7.25 0.512361 5.41 5.35 999A 24X 3W 62 67 213.95 7.50 0.512334 5.93 5.88 999A 24X 7W 36 41 219.67 7.75 0.512381 5.02 4.96 999A 25X 4W 100 105 225.43 8.00 0.512322 6.17 6.11 999A 26X 2W 14 19 231.17 8.25 0.512363 5.37 5.30 999A 26X 5W 128 133 236/91 8.50 0.512344 5.74 5.67 999A 27X 3W 52 57 242.65 8.75 0.512377 5.09 5.02 999A 28X 1W 18 23 248.91 8.98 0.512395 4.75 4.68 999A 28X 3W 32 36 252.04 9.10 0.512337 5.88 5.81

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34 Table 2 2. Continued Site Depth (mbsf) Age (Ma) a 143 Nd / 144 Nd b Nd(o) c Nd(t) d 999A 28X 4W 84 88 254.06 9.18 0.512360 5.42 5.35 999A 28X 5W 55 59 255.27 9.22 0.512474 3.21 3.14 999A 29X 1W 72 76 259.14 9.38 0.512546 1.79 1.72 999A 29X 2W 51 57 260.44 9.52 0.512498 2.73 2.66 999A 29X 4W 25 29 26 3.17 9.83 0.512555 1.63 1.55 999A 29X 6W 5 10 265.98 10.15 0.512414 4.37 4.29 265.98 10.15 0.512420 4.25 4.17 999A 29X 6W 66 70 266.58 10.22 0.512489 2.92 2.84 999A 29X 6W 104 109 266.97 10.26 0.512428 4.09 4.01 999A 30X 2W 3 8 269.56 10.46 0.512473 3.22 3.13 999A 30X 3W 59 63.5 271.61 10.56 0.512421 4.24 4.16 999A 30X 4W 8 14 272.61 10.61 0.512506 2.58 2.50 999A 30X 5W 2 7 274.05 10.69 0.512495 2.79 2.70 999A 30X 6W 105 110 276.58 10.78 0.512634 0.07 0.01 999A 30X 7W 28 33 277 .31 10.80 0.512508 2.53 2.45 999A 31X 2W 34 38 279.46 10.87 0.512628 0.19 0.11 999A 31X 3W 7 12 280.70 10.91 0.512506 2.58 2.50 999A 31X 4W 53 59 282.66 10.98 0.512494 2.80 2.72 999A 32X 1W 28 33 287.51 11.14 0.512550 1.72 1.63 287.51 11.14 0.512545 1.81 1.73 999A 32X 2W 90 94 289.62 11.21 0.512598 0.78 0.69 999A 32X 6W 18 23 294.91 11.39 0.512580 1.14 1.05 999A 32X 6W 79 84 295.52 11.41 0.512472 3.25 3.16 999A 33X 2W 4 10 298.27 11.50 0.512539 1.94 1.85 999A 33X 3W 4 8 299.76 11.55 0.512568 1.37 1.27 999A 33X 4W 106 111 302.29 11.63 0.512470 3.29 3.20 999A 33X 6W 65 69 304.87 11.72 0.512455 3.56 3.47 999A 33X CCW 13 18 305.96 11.77 0.512514 2.43 2.33 305.96 11.77 0.512509 2.53 2.52 999A 34X 2W 145 150 309.28 12 .01 0.512302 6.55 6.46 309.28 12.01 0.512319 6.22 6.13 309.28 12.01 0.512302 6.55 6.45 999A 34X 3W 63 67 309.95 12.06 0.512486 2.96 2.87 999A 34X 6W 100 105 314.83 12.41 0.512448 3.70 3.61 999A 34X 6W 118 122 315.00 12.43 0.512447 3.72 3 .63 999A 35X 3W 109 113 320.11 12.80 0.512486 2.96 2.86 999A 35X 5W 54 59 322.57 12.98 0.512514 2.42 2.32 322.57 12.98 0.512492 2.85 2.74 999A 35X 7W 17 21 325.19 13.17 0.512484 3.00 2.90 999A 37X 1W 15 19 335.37 13.39 0.512513 2.44 2.33 9 99A 37X 2W 6 11 336.79 13.42 0.512497 2.76 2.66 999A 38X 1W 55 60 345.38 13.69 0.512470 3.29 3.18 999A 38X 1W 69 73 345.51 13.70 0.512478 3.12 3.01 999A 38X 5W 55 60 351.38 14.01 0.512359 5.45 5.34

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35 Table 2 2. Continued Site Depth (mbsf) Age (Ma) a 143 Nd/ 144 Nd b Nd(o) c Nd(t) d 999A 39X 4W 94 99 359.87 14.50 0.512338 5.86 5.74 999A 42X 3W 133 138 387.75 16.00 0.512387 4.90 4.78 1241A 14H 3W 123 128 122.17 5.00 0.512480 3.09 3.04 1241A 16H 3W 47 52 140.40 5.50 0.512679 0. 80 0.85 1241A 19H 4W 77 82 170.73 6.00 0.512630 0.16 0.11 1241A 23H 3W 29 34 206.71 6.50 0.512685 0.91 0.97 1241A 25H 2W 0 5 223.95 7.00 0.512727 1.74 1.80 1241A 26H 1W 58 63 232.48 7.25 0.512685 0.91 0.98 1241A 27H 6W 79 84 249.76 7.75 0.512675 0.7 2 0.79 1241A 28H 3W 139 144 255.30 8.00 0.512628 0.20 0.13 1241A 29H 5W 49 54 266.91 8.25 0.512649 0.21 0.28 1241A 30H 4W 109 114 275.51 8.50 0.512651 0.25 0.33 1241A 31H 4W 19 24 284.12 8.75 0.512671 0.64 0.72 1241A 33H 2W 139 144 301.33 9.25 0.512 671 0.64 0.72 1241A 35X 3W 130 135 318.50 9.75 0.512701 1.23 1.31 1241A 40X 7W 40 45 371.10 11.25 0.512608 0.59 0.49 a Age models for all four sites are based on biostratigraphic boundaries and age datums defined Raffi and Flores [1995] at Site 846 and applied to Sites 998 and 999 by Kameo and Bralower [2000] and to Site 1241 by Mix et al. [2003]. b 143 Nd/ 144 Nd values analyzed on a given day were corrected by the difference between the average JNdi 1 value for that day and JNdi 1 = 0.512103 (TIMS av erage at University of Florida). b Nd(o) = [ 143 Nd/ 144 Nd (sample) / 143 Nd/ 144 Nd (CHUR) 1] 10 4 where 143 Nd/ 144 Nd (CHUR) = 0.512638. c Nd(t) = [ 143 Nd/ 144 Nd (sample (t)) / 143 Nd/ 144 Nd (CHUR(t)) 1] 10 4 d eat analyses of JNdi 1 is Nd units. Within run uncertaintie s w ere consistently less than this value.

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36 CHAPTER 3 MIOCENE DEEP WATER C IRCULATION IN THE PA CIFIC AND CARIBBEAN: IMPACTS OF THE CENTR AL AMERICAN S EAWAY AND SOUTHERN H EMISPHERE GLACIATION Overview During the Middle Miocene the eastern equatorial Pacific [ Vincent, 1981 ; Mayer et al., 1986 ; Farrell et al., 1995 ; Lyle et al., 1995], Caribbean [ Roth et al., 2000], and possibly the western Atlantic [ King et al., 1997] record ed intervals of extensive Lyle et al., 1995]. These intervals of low carbonate mass accumulation can be attributed to either increased productivity resulting in enhanced dec ay (oxidation) of organic matter on the seafloor or a change in global thermohaline circulation that resulted in more corrosive bottom water in the equatorial region of the Pacific and the Caribbean. Lyle et al. [1995] argued against increased surface prod uctivity and associated deep water acidity as a cause of the eastern equatorial Pacific carbonate crash based on an absence of increased organic carbon (C org ) or opal Mass Accumulation Rates (MARs), as well as a lack of a negative covariance between carbon ate and opal MARs. Instead, Lyle et al. [1995] and Roth et al. [2000] suggested carbonate crash events in both the Pacific and Caribbean were related to changes in circulation coinciding with shoaling of the Central American Seaway (CAS) in the Middle Mioc ene. Neodymium (Nd) isotopes recovered from fossil fish teeth provide a technique to investigate paleo circulation patterns and test this theory. Nd isotopes are quasi conservative tracers of water mass, meaning that the cores of different water masses hav e distinct Nd isotopic signatures that can only be altered through water mass mixing or addition of local weathering inputs [ Frank 2002; Goldstein and Hemming 2003].

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37 Important for this proxy is the fact that the residence time of Nd in the oceans [~600 1000 yrs; Elderfield and Greaves 1982; Piepgras and Wasserburg 1985; Jeandel et al. 1995; Tachikawa et al. 1999 ; Arsouze et al. 2009 ] is shorter than the modern ocean mixing time of ~1500 years [ Broecker and Peng 1982]. Fossil fish teeth and debris have been demonstrated to be a robust paleoceanographic archives of bottom water Nd isotopes [ Elderfield and Pagett 1986; Martin and Haley 2000; Thomas et al. 2003; Martin and Scher 2004; Thomas 2004; Scher and Martin 2006]. A previous study of Nd is otopes from the eastern equatorial Pacific and Caribbean during Miocene carbonate crash intervals demonstrated that the most corrosive waters had radiogenic isotopic values consistent with a North Pacific source and suggested Pacific water overflowed inter mediate to deep sills in the CAS to fill the deep Caribbean basin during the Caribbean carbonate crash [ Newkirk and Martin 2009]. Although Nd isotopes support the idea that carbonate crash intervals were genetically related to changes in ocean circulatio n during the Middle Miocene, the ultimate cause of these changes has yet to be identified. Based on the relative timing of the carbonate crash intervals and the history of the CAS, a number of studies suggest shoaling of the CAS played a major role in the evolution of Caribbean and Pacific circulation [e.g., Keigwin 1978; Farrell et al. 1995; Lyle et al. 1995; Collins et al. 1996; Ling et al. 1997; Haug and Tiedemann 1998; Frank et al. 1999; Reynolds et al. 2009; Roth et al. 2000; Haug et al. 2001 ; Steph et al. 2006; Jain et al. 2007; Groeneveld et al. 200 8 ; Newkirk and Martin 2009]. These studies tend to focus on changes in salinity related to development of the Isthmus of Panama and the resulting impact on the Gulf Stream and North Atlantic D eep Water (NADW) production, which ultimately impacts

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38 Pacific circulation via the global conveyor. However, there are also documented changes in Southern Ocean conditions during the Middle Miocene that could influence Pacific circulation. Specifically, the re is evidence for strengthening of the Antarctic Circumpolar Current (ACC) [ Shevenell et al. 2004], a marked increase in the production and export of Antarctic Bottom Water (AABW) [ Wright and Miller 1993], and increased flow speeds for the Deep Western Boundary Current (DWBC) exiting the ACC near Chatham Rise [ Hall et al. 2003] during the Middle Miocene climate transition (MMCT; 14.2 to 13.8 Ma [ Shevenell et al., 2004]) in conjunction with renewed growth of the East Antarctic Ice Sheet (EAIS) [ Kennett a nd Barker 1990] The primary goal of this study was to reconstruct deep water circulation in the eastern Pacific and Caribbean during the Miocene based on Nd isotopic records for fossil fish teeth/debris from a longitudinal transect of four Ocean Drillin g Project (ODP) sites in the eastern Pacific and expanded datasets for Caribbean records (Figure 3 1) in order to assess the relative roles of tropical CAS shoaling versus high latitude Southern Ocean climate change on Pacific and Caribbean circulation and development of carbonate crash intervals. A longitudinal transect of deep water Pacific sites runs from Site 845 (3704 m water depth) at 9 N through Site 846 (3296 m water depth) at 3S to Site 1237 (3212 m water depth) at 16S. These sites are ideally l ocated to study changes in the boundary between northern and southern sourced deep Pacific waters along the eastern margin of the basin as well as the impact of CAS gateway closure on the Pacific circulation. W e also extended the records from Newkirk and Martin [2009] for S ites 999 (12N in the Colombian Basin; 2839 m water depth) and Site 998 (19N in the Yucatan Basin;

PAGE 39

39 3101 m water depth) in the Caribbean Basin to further evaluate the impact of the CAS on conditions in the Caribbean.Data from Site 1241 (5N on the Cocos Ridge; 2027 m water depth) located just across the Isthmus of Panama from Site 999 represent the endmember for more intermediate depth waters that might have flowed into the Caribbean as the isthmus shoaled (Figure 3 1). All of t hese dat a are used to improve our understanding of processes driving circulation in the Pacific and Caribbean following the Mid Miocene Climatic Optima. Background Modern Pacific Deep Water Circulation Bottom water enters the Pacific Basin from the south as a de ep western boundary current (DWBC) that flows northward below 3000 m depth through deep passageways in the Southwest Pacific to fill the deep Pacific Ocean basin (Figure 3 2) [ Warren 1973, 1981; Lonsdale 1976; Carter et al. 1996, 1999; Carter and McCave 1997; Tsuchiya and Talley 1998; Carter and Wilkin 1999; Orsi et al. 1999 ]. There is also a branch off of the ACC that flows north up the eastern side of the Pacific [ Lonsdale 1976; Tsuchiya and Talley 1998 ] Both of these northward flowing water mass es are composed of Circumpolar Deep Water (CDW) a combination of AABW, Antarctic Intermediate Water (AAIW), NADW, and Pacific Deep Water (PDW) that mixes in the ACC [ Orsi et al. 1995, 1999; Rintoul et al. 2001]. The Nd isotopic composition of the Pacif ic has been shown to become progressively more radiogenic from south to north and from deep to intermediate water depths [ van de Flierdt et al. 2004 a ]. While transiting northward, CDW which starts with an Nd value of 8 [ Piepgras and Wasserburg 1982], accumulates nutrients and loses oxygen as a result of organic matter decay, and becomes more radiogenic due to

PAGE 40

40 mixing with southward flowing PDW [ van de Flierdt et al. 2004 a ]. Near the equator its Nd isotop ic composition is further modified to a value of ~ 5.2 [ Horikawa et al 2010] by boundary exchange with sediment from Papua New Guinea and adjacent volcanic islands in the Western Equatorial Pacific [ Lacan and Jeandel 2001] ; it is also influenced by reve rsible scavenging in the water column [ Horikawa et al. 2011] leading to the formation of modified CDW (mCDW) Once in the North Pacific, most mCDW upwells and flows southward along the eastern side of the basin at mid depths (1000 and 3000 m) as PDW (Fig ure 3 2) [ Schmitz 199 5; Reid 1997 ; K a wabe and Fujio 2010]. During this transit, it continues to accumulate nutrients and lose oxygen [ Matsumoto et al. 2002]. Today re circulated PDW obtains a radiogenic Nd isotopic value of ~ 2 as a result of reversibl e scavenging [ Horikawa et al. 2011] and interactions with young circum Pacific island arcs in the subarctic North Pacific. This water mass 13 C values in the Pacific [ Kroopnick 1985] and becomes progressively more corrosive with age and southward flow as a result of organic matter decay (remineralization) and associated increasing CO 2 concentrations. Overlying PDW is the nort hward flowing Antarctic Intermediate Water (AAIW) in the southern portion of the basin and southward flowing North Pacific Intermediate Water (NPIW) in the northern portion of the basin with the dividing line located in the equatorial region today [ Tsuchiy a and Talley 1998] These water masses flow at intermediate depths between ~500 to 1000 m (Figure 3 3) and can be distinguished by the fact that AAIW has lower nutrient s and higher oxygen as a result of substantial atmospheric interaction and incomplete nutrient depletion in the Southern Ocean

PAGE 41

41 [ Kroopnick 1985]. In contrast, NPIW forms from upwelling in the northwest Pacific and experiences relatively little to no atmospheric interaction [ Talley 1993]. The Peru and Guatemala Basins of the eastern Pacific (Figure 3 1) are isolated from northward flowing mCDW by the East Pacific Rise (EPR), which extends up to ~3000 m water depth. These two basins are separated by the Cocos Ridge, and the Galapagos Spreading Center In these basins t he deepest waters are c omposed of a northward flowing branch of CDW that originates from the circumpolar current in the s outheast Pacific Basin and mixes with PDW on its northward transit, creating a water Nd value s of ~ 3 [ Horikawa et al., 2010 ] Some of this water continues northward into the southern portion of the Peru Basin, flowing through the Peru Chile Trench (4900 m) near the Nazca Ridge and across a 3900 m sill [ Lonsdale 1976; Tsuchiya and Talley 1998]. Today there is a hydrologic divide in the Peru Basin; the deep water in the northern portion of the basin is PDW, while the deep water in the southern portion is CDW. The se northern and southern sourced deep water masses in the Peru Basin have similar te mperatures and salinities, but PDW is slightly less dense and tends to override CDW, which has higher oxygen concentrations and lower phosphate and nitrate concentrations [ Tsuchiya and Talley 1998]. Like the northern portion of the Peru Basin, the Guatema la Basin (Figure 3 1) to the north is filled with PDW Shoaling History of the Central American Seaway Although the closure history of the CAS is controversial [ Keigwin 1978; Marshall 1985; Webb 1985; Keller et al. 1989; Coates et al. 1992; Haug and Tiedemann 1998; Haug et al. 2001; Steph et al. 2006; Groeneveld et al. 2008, Montes et al. 2012], the general consensus is that closure started with uplift and arc formation approximately

PAGE 42

42 ~17 to 15 Ma [ Coates et al. 1992, 2003, 2004], with shoaling to a depth of ~2000 m by ~15.9 15.1 Ma [ Duque Caro 1990; ages adjusted to Shackleton et al. 1995], and continued shoaling to an upper bathyal depth of ~1000 m between 12 10.2 Ma [ Duque Caro 1990]. At this point, it is suggested that the minimum width of the gateway was ~200 km [ Montes et al. 2012]. Unlike Duque Caro [1990], Coates et al. [2003] suggested the seaway was shallower, and that an archipelago had developed by ~12 Ma. Oceanographic evidence suggests the seaway restricted deep and intermediate water flow from the Pacific into the Caribbean beginning at ~7.9 7.6 Ma based on shifts in benthic foraminiferal diversity and paleoproductivity differences between the Caribbean and eastern equatorial Pacific [ Jain et al. 2007]. Coates et al. [2004] also suggested continued shoaling related to collision of the volcanic arc and northern Colombia created a barrier to deep and intermediate waters by 7 Ma, consistent with the observed divergence of benthic organisms on either side of the CAS [ Keller et al. 1 989; Collins et al. 1996]. Continued shoaling to a depth of <100 m has been dated at 4.6 Ma [ Haug and Tiedemann 1998], with final closure occurring between ~4.2 2.4 Ma [ Keigwin 1978; Marshall 1985; Webb 1985; Keller et al. 1989; Coates et al. 1992 ; Haug and Tiedemann 1998; Haug et al. 2001; Steph et al. 2006; Groeneveld et al. 2008]. Material and Methods Core Descriptions and Age Model The age models applied to all six ODP sites in the study are based on the biostratigraphy of Sites 845 and 846 by Raffi and Flores [1995], which used zonal boundaries defined by Martini [1971] and Bukry [1973]. The ages of these zonal boundaries and magnetic reversals [ Mayer et al. 1992] were recalibrated to ages

PAGE 43

43 determined by Shackleton et al. [1995] using orbit al tuning. The age/depth models based on this biostratigraphy for Sites 1237 and 1241 come from Mix et al. [2003], while age models for Caribbean Sites 998 and 999 come from Kameo and Bralower [2000]. Pacific sites were sampled at a 0.25 Ma interval from 2 .5 to 14.6 Ma for Sites 845 and 846, 2.5 to 14 Ma at Site 1237, and 2.5 to 11.5 Ma (maximum depth) at Site 1241. The Caribbean sites were sampled at an interval of 0.25 Ma from 2.5 to ~18 Ma, with a higher resolution (~0.1 Ma) from 10 to 12 Ma. Ten samples were analyzed for Site 999 from 0.015 to 0.13 Ma. Sample Preparation and Nd Isotope Measurements Sediment samples were oven dried, disaggregated and wet sieved prior to hand dissolved in aqua regia, without prior cleaning [ Martin et al. 2010] and then dried prior to a two step chemical separation to isolate Nd. Bulk rare earth elements (REEs) were separated on primary quartz columns using Mitsubishi cation exchange resin [ Sc her and Martin 2004] or Teflon columns using Eichrom TRUspec TM Resin both used HCl as the eluent. Nd was then isolated from bulk REEs using Eichrom LNspec TM resin with HCl as the eluent on volumetrically calibrated Teflon columns [ Pin and Zalduegui 1997 ]. The total blank for th ese technique s is 14 pg Nd. Nd isotopic ratios were measured on a Nu Plasma Multi Collector Inductively Coupled Plasma Mass Spectrometer (MC ICP MS) at the University of Florida. The standard JNdi 1 was run between every 4 to 6 unk nown samples. All of the JNdi 1 values analyzed during a given day were averaged and compared to the published value of JNdi 1 (0.512115 0.000007) [ Tanaka et al. 2000] to determine the amount of correction to apply to the unknown samples analyzed that d ay. A drift correction was not

PAGE 44

44 applied to the data because variations throughout a day of analysis did not indicate a ICP MS based on the variability of normalized JNdi 1 analyzed over the past several years is 0.000014, which is Nd Nd represents the deviation in parts per 10 4 of the 143 Nd/ 144 Nd ratio of the sample relative to the chondritic uniform reservoir with 143 Nd/ 144 Nd=0.512638 [ Jacobsen and Wasserburg 1980]). 13 C Sample Pr eparation and Measurements Carbon isotopic ratios were measured on benthic foraminifera ( Cibicidoides ) foraminifera were cleaned in 15% H 2 O 2 sonicated, and dried with methanol. Samples were then reacted in 100% orthophosphoric acid at 70C using a Finnigan MAT Kiel III carbonate preparation device. The evolved CO 2 gas was measured online with a Finnigan MAT 252 mass spectrometer at the University of Florida. Isotopic results are reported in standard delta notation relative to Vienna Pee Dee Belemnite (VPDB). Analytical precision is estimated to be 0.018 13 C (1 standard deviation of standards run with samples). Results From 14 9 Ma the Nd isotopic ratios at all three e astern Pacific deepwater sites i ncrease d from values of ~ 3.5 at 14 Ma to 1.7 at 9 Ma (Figure 3 4 ; Table 3 1 ) This shift in Nd isotopes 13 C values from 14 to 9 Ma (Figure 3 5 ) Nd values of the two more northerly sites (Sites 845 and 846) diverge from values of the more southerly site (Site 1237) From 9 to 2.5 Ma value s for the northern sites fluctuate between 0.4 and 1.5 with an average

PAGE 45

45 value of ~1.3. For Nd values decreas e to ~ 3 (Fig ure 3 4 ) and fluctuate between 2 and 3.3 (Fig ure 3 4 ). Records from Sites 998 and 999 in the Caribbean start at values of ~ 2 to 3 at 18 Ma, decrease to ~ 5.5 by ~15 Ma, and then increase to values of 2 to 3.5 at ~13.5 Ma (Fig ure 3 6 ; Table 3 2 Nd values in the Caribbean from ~14 to ~9 Ma range from 5 to 0.4 with the most radiogenic values occurring from 12 to 1 0.7 Ma and overlapping with values recorded at intermediate depth Site 1241 from the Pacific. From ~10.7 to 2.5 Ma, Nd isotopic values gradually decrease from values of 2 to values of 8 to 9. The values in the youngest section of the record (0.13 to 0.0 1 Ma) fluctuate between 10.5 and 5.7. Discussion Circulation in the Eastern Pacific Based on records of Nd isotopes from fossil fish teeth/debris there are two distinct patterns of circulation in the eastern Pacific: 1) the period of increasing Nd values at all sites in the middle to late Miocene (14 to 9 Ma), and 2) the late Miocene to Pliocene interval (9 to 2.5 Ma), which is cha racterized by distinct values at the northern versus the southern sites (Figure 3 4 ). The Middle to Late Miocene Tr ansition (14 9 Ma) Nd values at all three sites in the e astern Pacific coincides with increases in the value of mCDW observed in Fe Mn crust VA13/2 in the equatorial Central Pacific [ Ling et al. 1997] and PDW from crust D4 13 A Alaska in the North Pacific [ van de Flierdt et al. 2004 a ] ( Figure 3 7 ) However, the magnitude of the Nd units in deep waters of the North Pacific (D4 13A Alaska [ van de Flierdt et al. 2004b]) and Nd units in the deep Centra l Pacific (VA 13/2 [ Ling et

PAGE 46

46 al. 1997]) Nd units in the deep eastern Pacific, indicating the shift in the eastern Pacific may in part reflect changes in the composition of the water sourcing PDW, but additional processes are also required Initially, Ling et al. [1997] attributed the isotopic increase in the Central Pacific to a decrease in the supply of a less radiogenic, presumably Atlantic sourced, water mass flowing into the Pacific through the CAS. Although some General Circulation Mo ) support this interpretation [ Maier Reimer et al. 1990; Mikolajewicz et al. 1993; Mikolajewicz and Crowley 1997; Nof and van Gorder 2003], Nd isotopic results of Newkirk and Martin [2009] demonstrate continued flow from the Pacific into th e Caribbean Basin during this time, in agreement with other GCM result s [ Nisancioglu et al. 2003; Klocker et al. 2005; Schneider and Schmittner 2006; Lunt et al. 2007]. Assuming the input value of the CDW end member from the Southern Ocean did not cha nge throughout this interval, as illustrated by Frank et al. [2002] and al. Nd values in the Central and North Pacific include either (1) the value of m CDW flowing into the North Pacific changed as a result of increased weathering inputs with radiogenic values and/or (2) the mixing boundary between northward flowing CDW and southward flowing PDW shifted to a position farther south and deeper in the water column. The first option is consistent with Ling et al. [2005], who revised their earlier ideas on the source of the seawate r Nd isotopic increase [ Ling et al ., 1997] and instead attributed it to increased volcanic activity and weathering of volcanic arcs around the Pacific. I ncrease d Pacific Island Arc production is observed from 18 1 1 Ma and 6 0 Ma [ Lee et al. 1995] but thi s timing is not consistent with the pattern of change observed throughout the Pacific.

PAGE 47

47 Also, Nd driven by volcanic inputs within the North Pacific sh ould produce the largest change in the north, but that region records the smallest change, with a slightly larger change in the Central Pacific and an even larger change in the eastern Pacific (Figure 3 7 ) Therefore, it is plausible that Nd units of the shift observed in the Central and eastern Pacific could be accounted for by increased volcanic input in the n orth Pacific, but the remainder of the documented increases must be the result of another process. Given that only part of the Nd isotopic increas e observed in all three eastern Pacific deepwater sites can be attributed to a change in the isotopic value of the source waters the remainder of the increase must be due to a change in the relative contribution s of more and less radiogenic components that comprise the deep water in this area. One potential scenario is southward progressio n and deepening of the mixing boundary between northward flowing CDW and southward flowing PDW (Figures 3 8 and 3 9 ), which could be related to a documented increase in the flux of DWBC entering the southern Pacific o ver the 5 my interval of increasing Nd isotopes [ Wright et al. 199 1 ; Hall et al. 2003]. E vidence supporting this increased flux includes strengthening of the ACC at the middle Miocene climate transition (MMCT; 14.2 to 13.8 Ma) [ Shevenell et al. 2004], increase d production and export of AABW based on Southern Ocean hiatuses [ Wright and Miller 1993] and increased flow speeds for the DWBC exiting the ACC near Chatham Rise based on sortable silt [ Hall et al. 2003]. All of these changes in the Southern Ocean coincided approximately with renewed growth of the EAIS [ Kennett and Barker 1990; Flower and Kennett 1995; Shevenell et al. 2004] as well as increased NADW production [ Wright and Miller 1996; Poore et al. 2006] All of

PAGE 48

48 these changes would have further strengthened the ACC, leading to a n increased flux of southern sourced waters into Pacific Ocean. This explanation is a bit counterintuitive because an increased flux of CDW with Nd values of ~ 7.5 to 8 [ 1998; Frank et al. 2002] into the Pacific would presumably decreas e the Nd isotopic value of deep water in the equatorial region [ Horikawa et al. 2011; van de Flierdt et al. 2004 a ], yet Nd isotopic data from the central equatorial region became more radiogenic at this time [ Ling et al. 1997]. T his paradox can be recon ciled if the increased flux of southern sourced deep waters into the Pacific led to a greater return flow of radiogenic ( Nd ~ 2) s out hward flowing water out of the n orth Pacific thereby shift ing the boundary with CDW deeper in the water column and further south ward (Figure s 3 8 and 3 9 ). Flower and Kennett [1995] document the encroachment of a low 13 C water mass (PDW) fr om the north to ~41S at 2000 to 3000 m depth in the southwest Pacific beginning ~ 14 to 13.6 Ma. A similar idea was proposed by van de Flierdt et al. [2004b], who attributed a shift in the Nd isotopic composition of seawater in the southwestern Pacific to the introduction of southward flowing waters from the equatorial region as a result of increased intensity of Southern Ocean circulation along with the shoaling of the Indonesian Seaway. Greater southward penetration of PDW would result in a more southerl y onset of mixing between CDW and PDW, thereby altering the initial Nd isotopic composition of northward flowing CDW prior to modification in the equatorial region, producing even more radiogenic mCDW that ultimately upwells in the n orth Pacific. The cohe rent shift to more radiogenic values at all three deep water sites (Sites 845, 846, and 1237) suggests that the sites were bathed by a water mass with a greater

PAGE 49

49 proportion of PDW by the end of the transition (Figure 3 9) This scenario suggests the core of PDW shifted to a depth of ~ 3000 m which is the approximate depth of the sills controlling the flow of deep water into the eastern equatorial Pacific basins This shift would have diminished the proportion of CDW that could enter these basins. These chan ges on the eastern side of the Pacific are consistent with expansion of the core of PDW in the southwestern Pacific documented by Flower and Kennett [ 19 95] in the late Miocene Southward encroachment of corrosive PDW from the n orth Pacific also agrees well with the observed progression of the carbonate crash in the eastern equatorial Pacific. Specifically, sites 845 and 1241 located just north of the equator recorde d a decrease in carbonate MARs beginning ~12 Ma, while extensive dissolution did not start un til ~11.2 Ma at Site 846 just south of the equator [ Farrell et al. 1995; Lyle et al. 1995], and Site 1237 recorded extensive carbonate dissolution [ Mix et al. 2003] (Figure 3 1). Similar to sites just north of the equator, carbonate dissolution began at ~12 Ma in the Caribbean Basin, but the Pacific event last ed ~1 my longer. In both basin s, onset of carbonate crash events is marked by a shift to more radiogenic Nd isotopic values indicating the wedge of corrosive PDW arrived in the eastern equatorial Pacific, bathed Sites 845 and 1241 and flowed through the CAS before the deeper portion of the wedge reached Site 846 (Figure 3 9 ). Therefore, the distribution of the Nd 13 C values and the southward progression of the onset of the carbonate crash suggest that the eastern Pacific basins were dominated by a mixture of CDW and PDW that was dominat ed by CDW prior to 14 Ma, and the

PAGE 50

50 proportion of PDW increased progressively as the boundary between the two water masses became deeper and extended southward (Figure 3 9 ). Late Miocene to Pliocene (8.5 to 2.5 Ma) Circulation T he Late Miocene to Pliocene c i rculation pattern was established around 9 to 8.5 Ma with the divergence of the more southerly site (Site 1237 ) to less radiogenic values (Figure 3 4 ). Plausible causes for the ~1 Nd unit decrease at Site 1237 include changes in volcanic ash input, increase d dust from the Atacama Desert, and/or a change in ocean circulation. Site 1237 recorde d an increase in ash layer frequencies in samples younger than ~9 Ma, with intervals of amp lified frequency from ~7.5 to 6, and from 5 to 1 Ma, possibly due to a major uplift of the northern Andes [ Mix et al. 2003]. The range Nd values reported for Andean volcanic material is highly variable and surprisingly some samples could drive down th Nd value [ Futa and Stern 1988; Rogers and Hawkesworth 198 9 ]; however, changes in the isotopic record do not coincide with changes in volcanic ash layer frequency and/or ash layer thickness reported by Mix et al. [2003]. This is especially tru e after ~5 Ma when all of the sites in the eastern Pacific record Nd signals are relatively constant (Figure 3 4 ) In terms of dust impacts, Jones et al. [ 199 4] and Ling et al. [2005] demonstrated that F e Mn nodules and crusts preserve the overlying water mass Nd isotopic composition even when it is distinct from the signal of eolian material in the sediment Data from the Peru Basin can also be used to argue the observed variations in seawater Nd isotope s were not driven by eolian inputs. The Atacama Desert is the prevailing source of dust to the Peru Basin today [ Molina Cruz 1977]. Increases in dust accumulation are observed at ~14 Ma at Site 1237, with a more prominent increase

PAGE 51

51 after ~8 Ma. These incre ases are related to aridification of the Atacama Desert [ Alpers and Brimhall, 1 988 ], possibly in response to Andean uplift. Observations of modern dispersal of dust throughout the Peru Basin [ Molina Cruz 1977] suggest that Sites 846 and 1237 receive simil ar dust inputs yet the offset in Nd isotopes observed in the late Miocene is also observed today [ Horikawa et al. 2011] Therefore volcanic and dust inputs cannot explain the divergence in Nd isotopes; instead we evaluate th is divergence in terms of wa ter mass distribution and circulation. The resulting Nd produces a pattern similar to the modern eastern Pacific in which the northern portion of the Peru Basin is dominated by more radiogenic PDW, while the southern portion of the basin i s dominated by a mixture of PDW and the less radiogenic CDW sourced from the southeast Pacific [ Horikawa et al. 2011] suggesting development of modern hydrographic conditions in the late Miocene The deeper boundary between PDW and CDW in the northern Pe ru Basin established by 8.5 Ma appears to become a permanent hydrographic feature of the eastern Pacific. In this configuration, the CDW PDW boundary was shallower than Site 1237 so the mixture of water was dominated by CDW in the southern portion of the P eru basin in the Miocene and probably had lower nutrients and higher dissolved oxygen to accompany the less radiogenic Nd isotopic composition compared to the mixture dominated by PDW in the northern portion of the basin as it does today [ Tsuchiya and Tal ley 1998; Horikawa et al. 2011] (Figure 3 9 ). The increased flow of CDW into the southern portion of the eastern Pacific occurred as a result of NADW production and the establishment of the Western Antarctic Ice Sheet (WAIS) [ Kennett and Barker 1990] wh ich led to further

PAGE 52

52 strengthening of the ACC and resulted in a shift of the boundary between PDW and CDW to a shallower depth in the southern portion of the Peru Basi n While onset of the carbonate crash in the Pacific and Caribbean was driven by the introd uction of corrosive n orth Pacific waters due to deepening of the PDW/CDW boundary, termination of the crash intervals appears to have different causes in the two regions. In the Pacific carbonate deposition recovered in some of the sites as they moved un der the equatorial productivity belt, despite the fact they were still bathed by corrosive PDW. I ncreased carbonate MARs and C org MARs at ~8 Ma at Pacific Site 846 mark the end of the carbonate crash and record enhanced surface productivity and an associat ed increase in carbonate rain rate which was large enough to allow for carbonate deposition within a corrosive environment [ Lyle et al. 1995]. In contrast, Site 845 in the Guatemala basin was never located in the productivity belt and n ever recovered fro m the carbonate crash. History of the Caribbean Basin The Nd isotopic values of ~ 2 to 5.5 at sites 998 and 999 prior to 14 Ma (Figure 3 10 ) plot between known values for Pacific and Atlantic waters, suggesting the Caribbean Basin was open to exchange with both ocean basins with waters entering over sills at intermediate to upper deepwater depths As noted in Newkirk and Martin [2009], the shift to more radiogenic values after ~14 Ma suggests a decrease in the contribution from the Atlantic and an incr ease in the flux from the Pacific with the basin fill ing almost completely from the Pacific, or possibly with a small fraction of Atlantic waters plus a very radiogenic shallow Pacific source General ocean circulation models of the Caribbean show a west t o east flow pattern with the bulk of waters shallower than 2000 m water depth flowing from the

PAGE 53

53 Pacific into the Caribbean with an open CAS due to steric height differences between the Pacific and Atlantic [ Lunt et al. 2007; Mikolajewicz and Crowley 1997; Nisancioglu et al. 2003; Prange and Schultz 2004; Schneider and Schmittner 2006; Steph et al. 2006]. Shoaling of the CAS to a depth of ~2000 m occurred between ~15.9 15.1 Ma (ages adjusted to Shackleton et al. [1995]) based on benthic foraminiferal assemblages from Atrato Basin located in northwest South America which roughly coincides with the timing of the shift to more radiogenic Nd isotopic values. Nd values in the Caribbean from ~14 to ~9 Ma are similar to those recorded in the Miocene Pacific (Figure 3 4 ) [ Abouchami et al. 1997; Ling et al. 1997, 2005; 1998; Frank et al. 1999; Reynolds et al. 1999; van de Flierdt et al. 20 04 a ; Newkirk and Martin 2009, and this study]. In particular, the Caribbean sites record a general increase in Nd isotopes that is similar to the increase observed at Sites 845 and 846 in the Pacific and has been attributed to encroachment of northern sou rced PDW that ultimately flowed into the Caribbean Basin. Nd values are highly variable with several spikes to values of ~0. Similar radiogenic values are recorded at intermediate depth Site 1241, located directly across the CAS in the Pacific (Figure 3 Nd values in t he Caribbean Basin have been suggested to reflect an influx of upper PDW to intermediate water through the CAS [ Newkirk and Martin 2009] and therefore a change in depth of the source water s from within the Pacific, rather than an increase in the relativ e proportion of Pacific water entering the basin. Duque Caro [ 1990] suggested the CAS had shoaled to upper bathyal depths (~1000 m) by this time, and Montes et al. [2012]

PAGE 54

54 suggested the opening between Panama and Columbia was restricted to less than ~200 km Given that Pacific values remain high and largely unchanged throughout this interval (Figure 3 10 ), decreasing Nd isotopic values from ~10.7 to 2.5 Ma in the Caribbean argue for a decreased flux of Pacific water into the Caribbean, consistent with the e nding of the carbonate crash in the Caribbean Basin at ~10 Ma as a result of s hoaling of the CAS Shoaling ultimately created the barrier to flow of corrosive Pacific deep and intermediate waters into the Caribbean Basin and allowed for the recovery from the carbonate crash Therefore, the changes in circulation and the carbonate crash were the results of changes in southern hemisphere climate, while the recovery of the carbonate crash in the Caribbean was the result of shoaling of the CAS. It is interesti ng to note that even after estimated dates for final closure of the CAS, (~4.2 2.4 Ma) [ Keigwin 1978; Keller et al. 1989; Coates et al. 1992; Haug et al. 2001; Steph et al. 2006 ; Groeneveld et al. 200 8 Nd values at Sites 998 and 999 do not appear to represent a pure n orth Atlantic source. Even Pleistocene samples that are less than 0.13 Ma continue to record values up to 6. The depth of flow into the Caribbean Basin on the Atlantic side is controlled by the Lesser Antilles and Aves Swell, which subsided from ~600 m to a modern depth of ~1200 m in the middle Miocene [ Pinet et al. 1985], producing two deep passageways the Windward and Anegada Jungfern Passages with modern sill depths of 1540 m and 180 0 m respectively [ Pinet et al. 1985]. These passages limit Atlantic inflow to intermediate depth and shallower water masses. Possible sources therefore include North Atlantic Intermediate Water Nd values of 13 to 12.5 at 2000 m on the Atlantic side of the Lesser

PAGE 55

55 Antilles [ Foster et al. 2007]; Glacial North Atlantic Intermediate Water (GNAIW) with values of 9.7 at 1790 m at Blake Nose [ Gutjahr et al. 2008]; and Antarctic Intermediate Water (AAIW) with values of 6 to 9 [ Jeandel 1993; Pahnke et al. 2008]. Using a composite dissolution index, Haddad and Droxler [1996] noted a shift between carbonate preservation and dissolution during the Pleistocene in the Caribbean Basin as a result of shifts in circulation on glacial/interglacial time scales. In this scenario, times of inc reased NADW production during interglacials result in encroachment of corrosive AAIW into the Caribbean Basin leading to in carbonate dissolution, while decreased/diminished NADW production during glacials resulted in introduction of less corrosive glacial North Atlantic Intermediate Water (GNAIW) into the Caribbean and enhanced carbonate preservation. Unfortunately at this time we do not have the resolution to fully evaluate this theory, but the range of Pleistocene Nd isotopes in the Caribbean do suggest variations between northe rn and southern sourced waters. By 7 Ma the decreasing Nd isotopic trend in the Caribbean had reached the Nd unit value obtained during times of known closure; thus, our data suggest continued flow of Pacific water through the CAS until at least 7 Ma, but beyond that the data do not allow us to more precisely define the age of final closure. Summary Nd isotopic analyses of Miocene to Pliocene fossil fish teeth/debris from a depth transect in the eastern equatorial Pacific and Caribbean Basin reveal that the dominant deep water mass in the eastern equatorial Pacific at ~14 Ma was southern sourced CDW that was over ridden by northern sourced, PDW. At that time the Caribbean Basin was filled with an undefined mixture of Pacific a nd Atlantic waters. Decreasing 13 C values from 14 Ma to 9 Ma at all three eastern Pacific deepwater sites are

PAGE 56

56 accompanied by increasing Nd isotopic values, consistent with increased contributions from an older water mass sourced from the north, indicating enhanced southward flow of PDW. Timing of this reorganization of circulation coincides with intensification of circulation in the Southern Ocean as a result of southern hemisphere glaciation. The Nd isotopic values and the pattern of o nset of the carbonat e crash in the northern equatorial Pacific sites and the Caribbean indicate that the introduction of the PDW into the equatorial region was responsible for the observed changes in carbonate MARs in th ese region These findings suggest the increased depth a nd southward progression of corrosive, radiogenic PDW into the equatorial region of the Pacific appears to be a response to strengthening of fluxes of circumpolar water into the Southern Pacific following climate change in the southern hemisphere Therefor e, this interpretation attributes changes in circulation in the eastern equatorial Pacific, as well as some of the changes i n the Caribbean and the onset of the carbonate crash in both regions to climate driven changes in the Southern Ocean rather than sho aling of the CAS.

PAGE 57

57 Figure 3 1. Bathymetric map of the Pacific Basin and Caribbean Basin [ Schlitzer, R., Ocean Data View, http://odv.awi.de 2012] illustrating the different basins of the eastern Pacific and the associated sills controlling the flow of deep water.

PAGE 58

58 Figure 3 2 Map of the Pacific Ocean [ Schlitzer, R., Ocean Data View, http://odv.awi.de 2012] illustrating the flow paths of Kawabe and Fujio [2010]. Dark blue represents the northward flowing Circumpolar Deep Water (CDW), while the green represents the southward flowing Pacific Deep Wa ter (PDW). O pen circles represent areas of upwelling of CDW to form PDW. The Ocean Drilling Program sites (Sites 845, 846, 1237 and 1241) are represented with red circles. Sites VA13/2, CD29 2, D4 13A Alaska, and 13D 27A Kamchatka are represented with the purple circles.

PAGE 59

59 Figure 3 3 North South Seawater profile for the central Pacific determined using the phosphate concentration profile for the modern Pacific ocean (modified from Horikawa et al. [2010])

PAGE 60

60 Figure 3 4 Seawater Nd isotopic values for the deep water sites (845, 846, and 1237) of the eastern Pacific compared to published values (shade fields) for the central Pacific [ Ling et al., 1997; ] and the north Pacific [ van de Flierdt et al. 2004a]. The middle Miocene Climatic Optimum (MMCO) [ Woodruff and Savin, 1989 ], middle Miocene Climate Transition (MMCT) [ Shevenell et al ., 2004], East Antarctic Ice Sheet development (EAIS) [ Kennett and Barker 1990], Caribbean Carbonate Crash (Caribbean C.C.) [ Roth et al ., 2000], Pacific Carbonate Crash (Pacific C.C.) [ Lyle et al. 1995], and West Antarctic Ice Sheet development [ Kennett and Barker 1990] are illustrated at the top of the figure.

PAGE 61

61 Figure 3 5 Nd isotopic values for the eastern Pacific ve r sus the carbon r ecord. Shaded box represents the carbonate crash interval(s) for the Pacific. Site 845 record ed the onset of carbonate dissolution at ~12 Ma. Dissolution at Site 846 began at ~11.2 Ma, while extensive carbonate dissolution was not recorded at Site 123 7.

PAGE 62

62 Figure 3 6 Seawater Nd isotopic data for Ocean Drilling Program Sites 998 and 999 in the Caribbean Basin Compared to the published values ( shaded fields ) for the Pacific [ Ling et al., 1997 Frank et al. 1999; van de Fl ierdt et al. 2004a,b] and the Atlantic [ Burton et al. 1997, 1999; 1998; Reynolds et al. 1999; Thomas and Via 2007].

PAGE 63

63 Figure 3 7 Changes in the Nd isotopic composition of water masses from the beginning of the record to 9 Ma from the central equatorial Pacific (Va 13/2) [ Ling et al 1997 ], the north Pacific (D4 13A Alaska) [ van de Flierdt et al. 2004 b], and the three eastern Pacific sites from this study (Sites 845, 846, and 1237).

PAGE 64

64 Figure 3 8 Nor th South Seawater profiles for the central Pacific showing the shifts in the boundaries between Pacific water mass. Boundaries were determined using the phosphate concentration profiles of the modern oceans and then adjusted based on the Nd isotopic compos ition observed in the Pacific from 14 to 2.5 Ma with Nd isotopic values for Va 13/2 [ Ling et al. 1997], CD29 2 [ Ling et al. 1997],and D4 13A Alaska and 13D 27A Kamchatka [ van de Flierdt et al. 2004 ]. The Nd isotopic value recorded at each site is listed next to the site name for each interval (a) Seawater profile illustrating the position of PD W for the Late Miocene to Pleistocene (8.5 to 2.5 Ma) which is the most similar to the modern distribution of water masses (b) profile for the beginning of the Middle to Late Miocene (14 Ma) and (c) profile for the end of the Middle to Late Miocene Mode (9 Ma)

PAGE 65

65 Figure 3 9 North South Seawater profiles for the eastern Pacific showing the shifts in the boundaries between Pacific water mass. Boundaries were determined using the phosphate concentration profiles of the modern oceans and then adjusted ba sed on the Nd isotopic composition observed in the Pacific from 14 to 2.5 Ma, with Nd isotopic values for Va 13/2 [ Ling et al. 1997], CD29 2 [ Ling et al. 1997], D4 13A Alaska and 13D 27A Kamchatka [ van de Flierdt et al. 2004 ], and sites 845, 846, 1237, 1241 from this study. The Nd isotopic value recorded at each site is listed next to the site name for each interval (a) Seawater profile illustrating the position of PDW during t he Late Miocene to Pleistocene (8.5 to 2.5 Ma) which is the most similar to the modern distribution of water masses (b) profile for the end of the Middle to Late Miocene M ode (9 Ma) and (c) profile for the beginning of the Middle to Late Miocene (14 Ma)

PAGE 66

66 Figure 3 10 Seawater Nd isotopic data for Ocean Drilling Program Sites 845, 846, 1237, and 1241 in the eastern Pacific, Sites 998 and 999 in the Car ibbean Basin, and BM1969.897 [ Reynolds et al., 1999] located in the Straits of Florida near Blake Nose. The shaded fields represent published values for the Pacific [ Ling et al., 1997 Frank et al. 1999; van de Flierdt et al. 2004a,b] and the Atlantic [ Burton et al. 1997, 1999; 1998; Reynolds et al. 1999; Thomas and Via 2007].

PAGE 67

67 Table 3 1 Nd isotopic results for the Pacific (Sites 845, 846, 1237, and 1241) Site Depth (mcd) Age (Ma) a 143 Nd/ 144 Nd b Nd(0) c Nd(T) d 845A 5H 6W 126 128 48.38 2.50 0.512569 1.3 1.3 0.3 845A 6H 1W 138 140 51.07 2.75 0.512583 1.1 1.0 0.3 845A 6H 3W 91 93 53.60 3.00 0.512574 1.2 1.2 0.3 845A 6H 5W 39 41 56.08 3.25 0.512563 1.5 1.4 0.3 845A 6H 6W 140 142 58.59 3.50 0.512580 1.1 1.1 0.3 845A 7H 1W 116 118 61.13 3.75 0.512564 1.4 1.4 0.3 845A 7H 3W 64 66 63.61 4.00 0.512541 1.9 1.9 0.3 845A 7H 5W 15 17 66.12 4.25 0.512570 1.3 1.3 0.3 845A 7H 6W 115 117 68.62 4.50 0.512557 1.6 1.5 0.3 845A 8H 2W 123 125 73.64 5.00 0.512572 1.3 1.2 0.3 845A 8H 4W 91 93 76.32 5.25 0.512571 1.3 1.3 0.3 845A 9H 1W 35 37 82.47 5.60 0.512558 1.6 1.5 0.3 845A 9H 3W 12 14 85.24 5.75 0.512558 1.6 1.5 0.3 845A 9H 5W 92 94 89.04 6.00 0.512569 1.3 1.3 0.3 845A 10H 1W 33 35 92.42 6.25 0.512535 2.0 1.9 0.3 845A 10H 3W 64 66 95.73 6.50 0.512535 2.0 1.9 0.3 845B 10H 3W 48 50 102.42 7.00 0.512580 1.1 1.1 0.3 845A 11H 2W 140 142 105.77 7.25 0.512577 1.2 1.1 0.3 845A 11H 5W 80 82 109.67 7.50 0.512537 2.0 1.9 0.3 845A 12H 1W 20 22 114.14 7.76 0.512586 1.0 0.9 0.3 845A 12H 3W 120 122 118.14 8.00 0.512538 2.0 1.9 0.3 845A 12H 6W 90 92 122.34 8.25 0.512546 1.8 1.7 0.3 845A 13H 2W 80 82 127.02 8.50 0.512571 1.3 1.2 0.3 845A 13H 5W 145 147 132.17 8.75 0.512540 1.9 1.8 0.3 845A 14H 2W 23 25 137.32 9.00 0.512544 1.8 1.7 0.3 845A 14H 5W 57 59 142.16 9.24 0.512550 1.7 1.6 0.3 845B 14H 2W 137 139 145.88 9.50 0.512522 2.3 2.2 0.3 845A 15H 2W 97 99 149.44 9.75 0.512524 2.2 2.1 0.3 845A 15H 5W 5 7 153.02 10.00 0.512513 2.4 2.4 0.3 845A 15H 7W 67 69 156.64 10.25 0.512510 2.5 2.4 0.3 845A 16H 2W 45 47 160.29 10.51 0.512500 2.7 2.6 0.3 845A 16H 4W 96 98 163.80 10.75 0.512492 2.8 2.7 0.3 845A 16H 6W 128 130 167.12 10.98 0.512495 2.8 2.7 0.3 845A 17H 2W 142 144 171.84 11.25 0.512500 2.7 2.6 0.3 845A 18H 3W 13 15 182.02 11.75 0.512473 3.2 3.1 0.3 845A 18H 6W 98 100 187.37 12.00 0.512493 2.8 2.7 0.3 845A 19H 4W 61 63 194.88 12.25 0.512508 2.5 2.4 0.3 845A 20H 2W 1 3 202.45 12.50 0.512481 3.1 2.9 0.3 845A 20H 7 7 9 210.01 12.75 0.512465 3.4 3.2 0.3 845A 21H 5W 14 16 217.48 13.00 0.512469 3.3 3.2 0.3

PAGE 68

68 Table 3 1 Continued Site Depth (mcd) Age (Ma) a 143 Nd/ 144 Nd b Nd(0) c Nd(T) d 845A 22H 2W 69 71 225.03 13.25 0.512470 3.3 3.2 0.3 845A 22H 6W 41 43 230.75 13.50 0.512466 3.4 3.2 0.3 845A 23X 3W 20 22 235.54 13.75 0.512479 3.1 3.0 0.3 845A 23X 6W 48 50 240.32 14.00 0.512438 3.9 3.8 0.3 845A 25X 1W 5 7 251.79 14.60 0.512478 3.1 3.0 0.3 846B 10H 1W 41 43 95.97 2.50 0.512584 1.1 1.0 0.3 846B 11H 2W 35 37 107.86 2.75 0.512572 1.3 1.3 0.3 846B 13H 1W 110 112 129.06 3.25 0.512568 1.4 1.3 0.3 846B 14H 1W 22 24 138.38 3.48 0.512612 0.5 0.5 0.3 846B 14H 1W 89 91 139.05 3.50 0.512611 0.5 0.5 0.3 846B 15H 4W 137 139 156.08 4.00 0.512569 1.4 1.3 0.3 846B 16H 3W 77 79 163.98 4.25 0.512618 0.4 0.3 0.3 846B 17H 2W 52 54 172.78 4.50 0.512578 1.2 1.1 0.3 846B 18H 3W 90 92 184.76 4.75 0. 512614 0.5 0.4 0.3 846B 19H 2W 115 119 194.97 5.00 0.512622 0.3 0.3 0.3 846B 19H 2W 117 119 194.98 5.00 0.512624 0.3 0.2 0.3 846B 20H 1W 48 50 204.09 5.25 0.512575 1.2 1.2 0.3 846B 21H 1W 100 102 215.46 5.50 0.512572 1.3 1.2 0.3 846B 22H 2W 58 60 229.54 5.75 0.512560 1.5 1.5 0.3 846B 23X 3W 8 10 243.59 6.00 0.512511 2.5 2.4 0.3 846B 24X 2W 143 145 254.54 6.25 0.512592 0.9 0.8 0.3 846B 25X 3W 143 145 265.44 6.50 0.512567 1.4 1.3 0.3 846D 25X 6W 62 64 272.03 6.75 0.512587 1.0 0.9 0.3 846B 27X 6W 47 49 288.28 7.25 0.512564 1.4 1.4 0.3 846B 28X 4W 102 104 295.53 7.43 0.512603 0.7 0.6 0.3 846B 29X 2W 132 134 302.13 7.75 0.512607 0.6 0.5 0.3 846B 29X 6W 61 67 307.44 8.09 0.512575 1.2 1.2 0.3 846B 30X 3W 110 116 313.13 8.43 0.512561 1.5 1.4 0.3 846B 31X 1W 77 83 319.40 8.81 0.512559 1.5 1.5 0.3 846B 31X 2W 101 107 321.14 8.92 0.512535 2.0 1.9 0.3 846B 31X 4W 98 104 324.11 9.10 0.512547 1.8 1.7 0.3 846B 31X 6W 101 107 327.14 9.29 0.512541 1.9 1.8 0.3 846B 32X 4 W 103 109 333.76 9.69 0.512546 1.8 1.7 0.3 846B 32X 6W 27 33 336.00 9.82 0.512542 1.9 1.8 0.3 846B 32X 6W 94 100 336.67 9.87 0.512544 1.8 1.7 0.3 846B 33X 1W 101 107 338.94 10.06 0.512566 1.4 1.3 0.3 846B 33X 2W 31 37 339.74 10.12 0.512538 2.0 1.9 0.3 846B 33X 4W 144 150 343.87 10.45 0.512539 1.9 1.8 0.3 846B 33X 6W 30 36 345.73 10.60 0.512522 2.3 2.2 0.3

PAGE 69

69 Table 3 1 Continued Site Depth (mcd) Age (Ma) a 143 Nd/ 144 Nd b Nd(0) c Nd(T) d 846B 34X 1W 140 146 348.93 10.78 0.512500 2.7 2.6 0.3 846B 34X 3W 121 127 351.74 10.93 0.512538 2.0 1.8 0.3 846B 34X 4W 111 117 353.14 11.01 0.512533 2.0 1.9 0.3 846B 34X 7W 21 27 356.74 11.21 0.512553 1.7 1.6 0.3 846B 35X 1 W 37 39 357.48 11.25 0.512510 2.5 2.4 0.3 846B 35X 4W 40 42 362.01 11.50 0.512509 2.5 2.4 0.3 846B 36X 2W 128 134 369.61 11.92 0.512503 2.6 2.5 0.3 846B 36X 3W 128 134 371.11 12.00 0.512493 2.8 2.7 0.3 846B 36X 6W 132 134 375.63 12.25 0.512529 2.1 2.0 0.3 846B 37X 2W 93 99 378.86 12.43 0.512532 2.1 2.0 0.3 846B 38X 1W 14 16 386.25 12.83 0.512505 2.6 2.5 0.3 846B 38X 4W 144 150 392.07 13.16 0.512502 2.7 2.5 0.3 846B 40X 1W 123 125 406.64 14.14 0.512458 3.5 3.4 0.3 846B 40X 4W 42 44 410.33 14.56 0.512453 3.6 3.5 0.3 1237C 5H 5W 116 120 47.88 2.50 0.512499 2.7 2.7 0.3 1237B 6H 2W 118 120 51.92 2.75 0.512485 3.0 3.0 0.3 1237C 6H 3W 115 117 55.95 3.00 0.512504 2.6 2.6 0.3 1237C 6H 6W 75 77 60.08 3.25 0.512494 2.8 2 .8 0.3 1237C 7H 5W 35 37 68.15 3.75 0.512510 2.5 2.5 0.3 1237B 8H 3W 97 99 72.23 4.00 0.512505 2.6 2.6 0.3 1237D 5H 1W 58 60 76.06 4.24 0.512479 3.1 3.1 0.3 1237D 5H 4W 78 80 80.79 4.50 0.512490 2.9 2.9 0.3 1237C 9H 3W 143 145 86.43 4.75 0.512 472 3.2 3.2 0.3 1237D 6H 4W 37 39 92.28 5.01 0.512518 2.3 2.3 0.3 1237C 10H 4W 73 75 97.78 5.25 0.512467 3.3 3.3 0.3 1237D 7H 4W 112 114 103.47 5.50 0.512520 2.3 2.2 0.3 1237D 8H 3W 28 30 110.68 5.75 0.512496 2.8 2.7 0.3 1237C 12H 4W 117 119 118.62 6.00 0.512494 2.8 2.8 0.3 1237B 13H 4W 87 89 126.47 6.25 0.512500 2.7 2.6 0.3 1237C 13H 6W 48 50 133.04 6.50 0.512522 2.3 2.2 0.3 1237B 14H 5W 77 79 138.05 6.75 0.512509 2.5 2.5 0.3 1237C 14H 3W 133 135 140.71 7.00 0.512536 2.0 1.9 0. 3 1237C 14H 5W 48 50 142.87 7.25 0.512515 2.4 2.3 0.3 1237B 15H 3W 43 45 145.01 7.50 0.512512 2.5 2.4 0.3 1237C 15H 3W 62 64 149.50 7.75 0.512496 2.8 2.7 0.3 1237C 15H 6W 52 54 153.93 8.00 0.512511 2.5 2.4 0.3 1237C 16H 4W 37 39 162.10 8.50 0. 512499 2.7 2.6 0.3 1237B 17H 4W 97 99 168.30 9.09 0.512550 1.7 1.6 0.3 1237B 17H 6W 63 65 170.97 9.34 0.512558 1.6 1.5 0.3

PAGE 70

70 Table 3 1 Continued Site Depth (mcd) Age (Ma) a 143 Nd/ 144 Nd b Nd(0) c Nd(T) d 1237C 17H 5W 143 145 175.13 10.01 0.512541 1.9 1.8 0.3 1237B 18H 3W 63 65 176.54 10.20 0.512533 2.1 2.0 0.3 1237B 18H 4W 97 99 178.39 10.45 0.512538 2.0 1.9 0.3 1237B 18H 5W 133 135 180.26 10.71 0.512512 2.5 2.4 0.3 1237C 18 H 3W 62 64 182.45 11.01 0.512529 2.1 2.0 0.3 1237C 18H 4W 88 90 184.22 11.25 0.512521 2.3 2.2 0.3 1237C 18H 5W 122 124 186.07 11.50 0.512492 2.9 2.7 0.3 1237B 19H 4W 2 4 188.92 11.75 0.512506 2.6 2.5 0.3 1237C 19H 2W 142 144 193.03 12.24 0.5125 18 2.4 2.2 0.3 1237B 20H 1W 17 19 194.83 12.46 0.512511 2.5 2.4 0.3 1237C 19H 5W 66 68 196.77 12.69 0.512501 2.7 2.6 0.3 1237B 20H 2W 77 79 196.94 12.71 0.512485 3.0 2.9 0.3 1237B 20H 3W 136 138 199.04 12.96 0.512496 2.8 2.6 0.3 1237B 20H 5W 51 53 201.20 13.21 0.512490 2.9 2.8 0.3 1237B 20H 6W 111 113 203.31 13.46 0.512473 3.2 3.1 0.3 1237C 20H 4W 62 64 205.76 13.75 0.512493 2.8 2.7 0.3 1237C 20H 5W 121 123 207.86 14.00 0.512497 2.8 2.6 0.3 1241A 7H 4W 115 116 64.10 2.55 0 .512676 0.7 0.8 0.3 1241A 8H 2W 94 96 72.05 2.85 0.512705 1.3 1.3 0.3 1241A 8H 6W 62 64 77.76 3.06 0.512671 0.6 0.7 0.3 1241A 9H 4W 12 14 84.68 3.29 0.512645 0.1 0.2 0.3 1241A 10H 1W 107 108 91.70 3.52 0.512696 1.1 1.2 0.3 1241A 10H 4W 126 128 96.39 3 .68 0.512621 0.3 0.3 0.3 1241A 11H 3W 54 56 104.77 3.96 0.512658 0.4 0.4 0.3 1241A 12H 1W 2 4 112.13 4.16 0.512698 1.2 1.2 0.3 1241A 12H 5W 4 6 118.19 4.32 0.512670 0.6 0.7 0.3 1241A 13H 4W 15 16 126.68 4.55 0.512647 0.2 0.2 0.3 1241A 14H 3W 124 126 136.34 4.81 0.512694 1.1 1.1 0.3 1241A 14H 3W 125 126 136.35 4.81 0.512492 2.9 2.8 0.3 1241A 15H 3W 86 88 146.01 5.06 0.512731 1.8 1.9 0.3 1241A 16H 3W 47 48 156.66 5.31 0.512691 1.0 1.1 0.3 1241A 17H 3W 9 10 166.35 5.54 0.512740 2.0 2.0 0.3 1241A 19H 4W 80 81 190.02 6.06 0.512642 0.1 0.1 0.3 1241A 22H 3W 119 121 221.39 6.52 0.512665 0.5 0.6 0.3 1241A 23H 3W 29 30 232.12 6.68 0.512697 1.1 1.2 0.3 1241A 25H 2W 4 5 252.80 6.98 0.512739 2.0 2.0 0.3 1241A 26H 1W 58 59 262.52 7.24 0.512697 1.1 1.2 0. 3 1241A 26H 1W 59 61 262.53 7.24 0.512716 1.5 1.6 0.3 1241A 26H 7W 19 20 271.18 7.49 0.512760 2.4 2.4 0.3

PAGE 71

71 Table 3 1 Continued Site Depth (mcd) Age (Ma) a 143 Nd/ 144 Nd b Nd(0) c Nd(T) d 1241A 26H 7W 20 22 271.19 7.49 0.512697 1.2 1.2 0.3 1241A 27H 6W 83 84 280.82 7.76 0.512687 1.0 1.0 0.3 1241A 28H 3W 140 141 287.76 7.96 0.512640 0.0 0.1 0.3 1241A 29H 5W 49 50 300.11 8.32 0.512661 0.4 0.5 0.3 1241A 30H 4W 109 110 3 09.86 8.61 0.512663 0.5 0.6 0.3 1241A 31H 4W 19 20 319.41 8.90 0.512683 0.9 1.0 0.3 1241A 32H 3W 80 82 331.05 9.16 0.512630 0.2 0.1 0.3 1241A 33H 2W 143 144 342.73 9.39 0.512683 0.9 1.0 0.3 1241A 34H 2W 54 56 352.58 9.58 0.512664 0.5 0.6 0.3 1241A 3 5X 3W 130 131 361.96 9.76 0.512713 1.5 1.5 0.3 1241A 36X 3W 91 93 371.74 9.96 0.512726 1.7 1.8 0.3 1241A 38X 2W 30 31 391.43 10.40 0.512688 1.0 1.1 0.3 1241A 39X 1W 91 93 401.28 10.63 0.512642 0.1 0.2 0.3 1241A 40X 7W 41 43 420.74 11.07 0.512610 0.5 0.4 0.3 1241A 41X 5W 41 42 428.59 11.25 0.512620 0.4 0.3 0.3 1241A 42X 5W 31 32 439.45 11.50 0.512651 0.3 0.4 0.3 a Age models are described in the methods section. b 143 Nd/ 144 Nd values analyzed on a given day were corrected by the difference between the average JNdi 1 value for that day and JNdi 1 = 0.512103 (TIMS average at University of Florida). b Nd(o) = [ 143 Nd/ 144 Nd (sample) / 143 Nd/ 144 Nd (CHUR) 1] 10 4 where 143 Nd/ 144 Nd (CHUR) = 0.512638. c Nd(t) = [ 143 Nd/ 144 Nd (sample (t)) / 143 Nd/ 144 Nd (CHUR(t)) 1] 10 4 d 1 is 0.00 Nd units. Within run uncertainties were consistently less than this value.

PAGE 72

72 Table 3 2 Nd isotopic results for the Caribbean Basin (Sites 998A and 999A) Site Depth (mbsf) Age (Ma) a 143 Nd/ 144 Nd b Nd(o) c Nd(T) d 998A 1H 1W 10 16 0.13 0.15 0.512102 10.5 10.4 0.3 998A 6H 3W 35 38 50.18 2.50 0.512204 8.5 8.4 0.3 998A 6H 6W 43 46 54.76 2.75 0.512164 9.2 9.2 0.3 998A 7H 2W 146 149 59.29 3.00 0.512208 8.4 8.4 0.3 998A 7H 6W 5 8 63.88 3.25 0.5122 00 8.5 8.5 0.3 998A 8H 2W 116 119 68.49 3.50 0.512190 8.7 8.7 0.3 998A 8H 5W 122 125 73.05 3.75 0.512215 8.2 8.2 0.3 998A 9H 2W 80 83 77.63 4.00 0.512229 8.0 7.9 0.3 998A 9H 5W 88 91 82.21 4.25 0.512248 7.6 7.6 0.3 998A 10H 2W 46 49 86.79 4. 50 0.512272 7.1 7.1 0.3 998A 10H 5W 54 57 91.37 4.75 0.512228 8.0 8.0 0.3 998A 11H 2W 12 15 95.95 5.00 0.512285 6.9 6.8 0.3 998A 11H 5W 20 23 100.53 5.25 0.512294 6.7 6.7 0.3 998A 11H 6W 130 133 103.13 5.39 0.512298 6.6 6.6 0.3 998A 12H 2W 1 4 105.34 5.75 0.512324 6.1 6.1 0.3 998A 12H 3W 67 70 107.50 6.00 0.512328 6.0 6.0 0.3 998A 12H 4W 140 143 109.73 6.25 0.512287 6.8 6.8 0.3 998A 12H 6W 60 63 111.93 6.50 0.512324 6.1 6.1 0.3 998A 13H 1W 76 79 114.09 6.75 0.512324 6.1 6.1 0.3 998A 13H 2W 146 149 116.29 7.00 0.512402 4.6 4.5 0.3 998A 13H 4W 67 70 118.55 7.26 0.512318 6.2 6.2 0.3 998A 13H 5W 138 141 120.76 7.51 0.512451 3.6 3.6 0.3 998A 14H 1W 7 10 122.90 7.75 0.512463 3.4 3.4 0.3 998A 14H 2W 73 76 125.05 8.00 0.5123 24 6.1 6.1 0.3 998A 14H 3W 146 149 127.28 8.25 0.512335 5.9 5.8 0.3 998A 14H 5W 66 69 129.48 8.50 0.512361 5.4 5.3 0.3 998A 14H 6W 137 140 131.69 8.87 0.512507 2.6 2.5 0.3 998A 15H 1W 21 26 132.53 8.95 0.512312 6.4 6.3 0.3 998A 15H 3W 107 11 3 136.40 9.33 0.512335 5.9 5.8 0.3 998A 15H 5W 27 32 138.60 9.52 0.512328 6.0 6.0 0.3 998A 16H 1W 54 59 142.37 9.83 0.512391 4.8 4.8 0.3 998A 16H 3W 125 129 146.08 10.14 0.512363 5.4 5.3 0.3 998A 16H 4W 32 37 146.65 10.18 0.512413 4.4 4.3 0.3 998A 16H 4W 45 50 146.78 10.19 0.512469 3.3 3.2 0.3 998A 16H 5W 25.5 30 148.07 10.30 0.512390 4.8 4.8 0.3 998A 16H 6W 32 36 149.64 10.46 0.512412 4.4 4.3 0.3 998A 16H 6W 125 130 150.58 10.59 0.512503 2.6 2.6 0.3 998A 17H 1W 21 26 151.54 10.73 0.512508 2.5 2.5 0.3 998A 17H 1W 32 37 151.65 10.75 0.512557 1.6 1.5 0.3 998A 17H 1W 77 82 152.10 10.82 0.512510 2.5 2.4 0.3

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73 Table 3 2 Continued Site Depth (mbsf) Age (Ma) a 143 Nd/ 144 Nd b Nd(o) c Nd(T) d 998A 17H 1W 105 110 152.38 10.86 0.512478 3.1 3.0 0.3 998A 17H 2W 25 30 153.08 10.98 0.512452 3.6 3.6 0.3 998A 17H 2W 54 60 153.37 11.02 0.512488 2.9 2.8 0.3 998A 17H 2W 126 131 154.09 11.14 0.512461 3.5 3.4 0.3 998A 17H 4 W 55 60 156.38 11.50 0.512586 1.0 0.9 0.3 998A 17H 5W 2 7 157.35 11.65 0.512452 3.6 3.5 0.3 998A 17H 5W 134 139 158.67 11.82 0.512503 2.6 2.5 0.3 998A 17H 6W 26 31 159.09 11.87 0.512649 0.2 0.3 0.3 998A 17H 6W 81 87 159.64 11.93 0.512606 0.6 0. 5 0.3 998A 17H CCW 2 7 160.65 12.04 0.512644 0.1 0.2 0.3 998A 18X 1W 105 111 161.88 12.17 0.512432 4.0 3.9 0.3 998A 18X 3W 32 36 164.14 12.42 0.512469 3.3 3.2 0.3 998A 19X 1W 53 58 166.76 12.70 0.512430 4.1 4.0 0.3 998A 19X 5W 24 28 172.46 13.50 0.512457 3.5 3.4 0.3 998A 20X 2W 32 36 177.74 14.05 0.512446 3.8 3.6 0.3 998A 20X 5W 60 63 182.52 14.50 0.512518 2.3 2.2 0.3 998A 21X 5W 56 59 192.08 15.41 0.512358 5.5 5.3 0.3 998A 22X 1W 13 16 195.25 15.71 0.512408 4.5 4.4 0.3 998A 22X 3W 22 25 198.34 16.00 0.512447 3.7 3.6 0.3 998A 23X 2W 64 66 206.96 16.50 0.512448 3.7 3.6 0.3 998A 24X 2W 146 149 217.38 17.00 0.512432 4.0 3.9 0.3 998A 25X 3W 77 79 227.79 17.50 0.512411 4.4 4.3 0.3 998A 26X 4W 8 10 238.19 18.00 0.512526 2.2 2.0 0.3 999A 1H 1W 59 61 0.60 0.00 0.512346 5.7 5.7 0.3 999A 1H 1W 122 124 1.23 0.00 0.512221 8.1 8.1 0.3 999A 1H 1W 132 134 1.33 0.00 0.512242 7.7 7.7 0.3 999A 1H 1W 142 144 1.43 0.00 0.512308 6.4 6.4 0.3 999A 1H 2W 40 42 1.91 0.00 0. 512290 6.8 6.8 0.3 999A 1H 2W 93 95 2.44 0.01 0.512248 7.6 7.6 0.3 999A 1H 3W 131 132 4.32 0.01 0.512291 6.8 6.8 0.3 999A 1H 3W 133 135 4.34 0.01 0.512262 7.3 7.3 0.3 999A 1H 4W 12 14 4.63 0.01 0.512237 7.8 7.8 0.3 999A 1H 4W 73 75 5.24 0.01 0.512187 8.8 8.8 0.3 999A 9H 6W 93 97 82.55 2.51 0.512247 7.6 7.6 0.3 999A 10H 5W 69 71 90.30 2.75 0.512206 8.4 8.4 0.3 999A 11H 4W 58 60 98.19 3.00 0.512247 7.6 7.6 0.3 999A 12H 3W 55 58 106.17 3.25 0.512226 8.0 8.0 0.3 999A 13H 2W 47 50 1 14.09 3.50 0.512291 6.8 6.7 0.3 999A 14H 1W 38 41 122.00 3.75 0.512251 7.5 7.5 0.3

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74 Table 3. 2 Continued Site Depth (mbsf) Age (Ma) a 143 Nd/ 144 Nd b Nd(o) c Nd(T) d 999A 14H 6W 82 85 129.97 4.00 0.512322 6.2 6.1 0.3 999A 15H 5W 70 72 137.84 4.25 0.512346 5.7 5.7 0.3 999A 16H 3W 147 150 145.09 4.50 0.512335 5.9 5.9 0.3 999A 17H 1W 69 71 150.79 4.75 0.512285 6.9 6.8 0.3 999A 17H 5W 42 4 6.5 156.56 5.00 0.512313 6.3 6.3 0.3 999A 18H 2W 117 120 162.29 5.25 0.512341 5.8 5.8 0.3 999A 18H 6W 90 95 168.03 5.50 0.512338 5.9 5.8 0.3 999A 19H 4W 14 19 173.77 5.75 0.512350 5.6 5.6 0.3 999A 20H 1W 88 93 179.51 6.00 0.512321 6.2 6.1 0.3 999A 20H 5W 63 65 185.24 6.25 0.512787 2.9 3.0 0.3 999A 21H 1W 137 139 189.48 6.43 0.512222 8.1 8.1 0.3 999A 21H 6W 108 110 196.69 6.75 0.512320 6.2 6.2 0.3 999A 23X 2W 34 39 202.47 7.00 0.512300 6.6 6.5 0.3 999A 23X 6W 8 13 208.21 7.25 0.51237 0 5.2 5.2 0.3 999A 24X 3W 62 67 213.95 7.50 0.512343 5.8 5.7 0.3 999A 24X 7W 36 41 219.69 7.75 0.512393 4.8 4.7 0.3 999A 25X 4W 100 105 225.43 8.00 0.512334 5.9 5.9 0.3 999A 26X 2W 14 19 231.17 8.25 0.512372 5.2 5.1 0.3 999A 26X 5W 128 131 2 36.91 8.50 0.512353 5.6 5.5 0.3 999A 27X 3W 52 57 242.65 8.75 0.512387 4.9 4.8 0.3 999A 28X 1W 18 23 248.91 8.98 0.512411 4.4 4.4 0.3 999A 28X 3W 32 36 252.04 9.10 0.512347 5.7 5.6 0.3 999A 28X 4W 84 88 254.06 9.18 0.512372 5.2 5.1 0.3 999A 28X 5W 55 59 255.27 9.22 0.512484 3.0 2.9 0.3 999A 29X 1W 72 76 259.14 9.38 0.512558 1.6 1.5 0.3 999A 29X 2W 51 57 260.44 9.52 0.512519 2.3 2.3 0.3 999A 29X 4W 25 29 263.17 9.83 0.512565 1.4 1.3 0.3 999A 29X 6W 5 10 265.98 10.15 0.512427 4.1 4.0 0.3 999A 29X 6W 66 70 266.58 10.22 0.512499 2.7 2.6 0.3 999A 29X 6W 104 109 266.97 10.26 0.512432 4.0 3.9 0.3 999A 30X 1W 128 132 269.30 10.45 0.512427 4.1 4.0 0.3 999A 30X 2W 3 8 269.56 10.46 0.512483 3.0 2.9 0.3 999A 30X 3W 59 63.5 271.6 1 10.56 0.512431 4.0 4.0 0.3 999A 30X 4W 8 14 272.61 10.61 0.512516 2.4 2.3 0.3 999A 30X 5W 2 7 274.05 10.69 0.512505 2.6 2.5 0.3 999A 30X 6W 105 110 276.58 10.78 0.512659 0.4 0.5 0.3 999A 30X 7W 28 33 277.31 10.80 0.512518 2.3 2.3 0.3 999A 31 X 2W 34 38 279.46 10.87 0.512640 0.0 0.1 0.3 999A 31X 3W 7 12 280.70 10.91 0.512516 2.4 2.3 0.3 999A 31X 4W 53 59 282.66 10.98 0.512506 2.6 2.5 0.3

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75 Table 3. 2 Continued Site Depth (mbsf) Age (Ma) a 143 Nd/ 144 Nd b Nd(o) c Nd(T) d 999A 32X 1W 28 33 287.51 11.14 0.512551 1.7 1.6 0.3 999A 32X 2W 90 94 289.62 11.21 0.512610 0.5 0.5 0.3 999A 32X 6W 18 23 294.91 11.39 0.512590 0.9 0.8 0.3 999A 32X 6W 79 84 295.52 11.41 0.512482 3.0 3.0 0.3 999A 33X 2W 4 10 298.27 11.50 0.512565 1.4 1.3 0.3 999A 33X 3W 4 8 299.76 11.55 0.512580 1.1 1.0 0.3 999A 33X 4W 106 111 302.29 11.63 0.512480 3.1 3.0 0.3 999A 33X 6W 68 69 304.87 11.72 0.512463 3.4 3.3 0.3 999A 33X CCW 13 18 305.96 11.77 0.512512 2.5 2.4 0.4 999A 34X 2W 145 150 309.28 12.01 0.512318 6.3 6.2 0.4 999A 34X 3W 63 67 309.95 12.06 0.512498 2.7 2.6 0.3 999A 34X 6W 100 105 314.83 12.41 0.512462 3.4 3.3 0.3 999A 34X 6W 118 122 315.00 12.43 0.512459 3.5 3.4 0.3 999A 35X 3W 109 113 320.1 1 12.80 0.512498 2.7 2.6 0.3 999A 35X 5W 54 59 322.57 12.98 0.512508 2.5 2.4 0.4 999A 35X 7W 17 21 325.19 13.17 0.512496 2.8 2.7 0.3 999A 37X 1W 15 19 335.37 13.39 0.512525 2.2 2.1 0.3 999A 37X 2W6 11 336.79 13.42 0.512507 2.6 2.5 0.3 999A 3 8X 1W 55 60 345.38 13.69 0.512480 3.1 3.0 0.3 999A 38X 1W 69 73 345.51 13.70 0.512490 2.9 2.8 0.3 999A 38X 5W 55 60 351.38 14.01 0.512369 5.2 5.1 0.3 999A 39X 4W 94 99 359.87 14.50 0.512347 5.7 5.6 0.3 999A 40X 4W 64 66 369.15 15.00 0.512352 5 .6 5.5 0.3 999A 41X 4W 21 23 378.42 15.50 0.512407 4.5 4.4 0.3 999A 42X 3W 133 138 387.76 16.00 0.512396 4.7 4.6 0.3 999A 44X 1W 82 84 403.33 16.50 0.512400 4.6 4.5 0.3 999A 45X 3W 107 110 416.19 17.00 0.512426 4.1 4.0 0.3 999A 46X 5W 122 125 429.04 17.50 0.512414 4.4 4.2 0.3 999A 47X 5W 140 142 438.81 17.88 0.512468 3.3 3.2 0.3 a Age models are described in the methods section b 143 Nd/ 144 Nd values analyzed on a given day were corrected by the difference between the average JNdi 1 value for that day and JNdi 1 = 0.512103 (TIMS average at University of Florida). b Nd(o) = [ 143 Nd/ 144 Nd (sample) / 143 Nd/ 144 Nd (CHUR) 1] 10 4 where 143 Nd/ 144 Nd (CHUR) = 0.512638. c Nd(t) = [ 143 Nd/ 144 Nd (sample (t)) / 143 Nd/ 144 Nd (CHUR(t)) 1] 10 4 d ternal uncertainty based on normalized repeat analyses of JNdi 1 is Nd units. Within run uncertainties were consistently less than this value.

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76 CHAPTER 4 T RANSCONTINENTAL CONN ECTION OF THE AMAZON RIVER B ASED ON CEARA RISE SEAWATER RECORD S Overview The Ceara Rise in the topical Atlantic is located midway between n orth ern and s outh ern deep water sources Ocean Drilling Program (ODP) sites on the rise cover a range of depth s from ~3000 4300 m (Figure 4 1) a nd are frequently used to track the boundary between Northern Component Water (NCW; proto North Atlantic Deep Water) and Antarctic Bottom Water (AABW) in the Oligocene/Miocene [ Flower et al. 1997 ] and early Pliocene [ Billups et al. 1998] based on carbon isotopes King et al. [1997] used magnetic susceptibility, natural gamma, and digital reflectance of lithology to determine the percent carbonate deposition at Ceara Rise. Episodes of carbonate dissolution between 14 and 1 0 .5 Ma were observed and were sugg ested to be the result of a shallower lysocline related to a shift in the boundary between NCW and AABW More dissolution is consistent with a greater proportion of older, more corrosive AABW at these depths The return of carbona te deposition starting ~10 .5 Ma was attributed to a shift in the AABW NCW boundary as a result of increased NCW production based on results from Wright and Miller [1992] [ King et al., 1997]. Most basin wide to global studies of the production rate of NCW have been based on the gra 13 C in the Atlantic and Pacific [ Wright et al. 1996; Poore et al. 2006], but that proxy is complicated in the Miocene by the fact th at the gradient is very small. 13 C is altered by changes in the nutrient signals which change s along the flow path of a water mass and therefore indicates the age rather than the composition of a water mass [ Kroopnick 1985 ] To better constrain how the boundary between AABW and NCW changed as a result of changes in the production rate of both NA DW and AABW we

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77 used Nd isotopes which are considered to be quasi conservative tracer s of water mass [ Frank 2002; Goldstein and Hemming 2003 ] Like a true conservative tracer of water mass, the modern residence time of Nd in the oceans [~600 1000 yrs; E lderfield and Greaves 1982; Piepgras and Wasserburg 1985; Jeandel et al. 1995; Tachikawa et al. 1999; Arsouze et al. 2009] is shorter than the ocean mixing time [ ~1500 years ; Broecker and Peng 1982] ; however, they reflect the initial signal of the so urce region, but can be modified by weathering inputs during circulation Fossil fish teeth and debris were analyzed because they have been shown to be robust paleoceanographic archives of bottom water Nd isotopes [ Elderfield and Pagett 1986; Martin and H aley 2000; Thomas et al. 2003; Martin and Scher 2004; Thomas 2004; Scher and Martin 2006]. The depth transect of ODP Sites 925, 926 and 929 (~3000 to 4300 m) on Ceara Rise encompasses the modern mixing boundary between AABW and NADW (based on tempera ture and salinity), which falls close to the deepest site (929) (Figure 4 2) T hese two water masses have distinct Nd isotopic compositions with modern values of 13.5 for NADW and 8 for AABW [ Piepgras and Wasserburg 1982; Piepgras and Wasserburg 1987; Jeandel 1993] and Miocene values of ~ 11 for NCW and ~ 8 for Documentation of seaw a ter Nd isotopic r ecords at this depth transect should allow us to reconstruct the position of this interface through time a nd determine whether there is a direct correlation between carbonate dissolution and the influx of AABW over the Ceara Rise. It would a lso provide information about relative NCW and AABW production rates

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78 Early results of seawater Nd isotopic analyses indi cated the seawater values at these open ocean sites were strongly influenced by a signal from Amazon sediments. Thus, this study was refocused to understand the impact of Amazon outflow on seawater Nd isotopes and the history of the Amazon basin pre served in the isotopic record. Andean uplift events during the Late Miocene have been identified as important factors in the evolution of the Amazon River drainage basin [ Hoorn, 1993; Hoorn 1994; Hoorn e t al. 1995; Campbell et al. 2006; Figueiredo et al. 2009 2010; Hoorn et al., 2010 ]. Prior to these events, Hoorn (1995) argued that the early Miocene proto Amazon River drained into the Caribbean Basin rather than connecting to the Atlantic and Andean uplift is credited with producing a transcontinental conne ction with development of the Amazon Basin and outflow to the Atlantic [ Castro et al., 1978; Campbell, 1992; Hoorn, 1993; Hoorn 1994; Hoorn e t al. 1995; Campbell et al. 2006; Figueiredo et al. 2009, 2010; Campbell 2010; Hoorn et al., 2010] ; however, t he timing of this evolution is debated. In its modern configuration the sediments that comprise the Amazon Fan are derived from both the Andes and the lowlands of Brazil, but the detrital fraction is dominated by the Andean highlands [ Gibbs 1967; Millima n 1979; Damuth et al. 1988; McDaniel et al. 1997; Dobson et al. 1997; Dobson et al. 2001]. Estimates for development of the Amazon River and Fan range from the end of the middle/late Miocene to the late Pliocene [ Castro et al., 1978; Campbell, 1992; H oorn, 1993; Hoorn 1994; Hoorn e t al. 1995; Campbell et al. 2006; Figueiredo et al. 2009, 2010; Campbell 2010; Hoorn et al., 2010]. Figueiredo et al. [2009] used biostratigraphic, isotopic, and well log data to show that during the early to middle Mioc ene the sediment

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79 reaching the Amazon Fan region was derived from the lowland cratons, but from the late Miocene to present the sediment has predominantly been derived from the Andes and attributed the fan development to the onset of a transcontinental conn ection of the Amazon. Prior to the transcontinental connection during the late middle Miocene, Hoorn et al. [1995] argues Andes uplift altered the northwest Amazonia region causing proto Amazon River formation but argues this proto Amazon does not actually flow east to the Atlantic until continued Andes uplift causes a shift in the Amazon drainage basin allowing for a transcontinental connection in the late Miocene. Harris and Mix [2002] used shifts in the clay mineralogy sourced from the Amazon River and r eaching Ceara Rise to determine the timing of c hanges in the Amazon drainage basin. The clay mineralogy showed a shift from material sourced from a region dominated by chemical weathering ( interpreted as sourced from the Amazon Lowlands) to material source d from a region dominated by physical weathering ( interpreted as sourced from the Andean Highlands) at 8 Ma and another event at ~4.5 Ma The shift at 8 Ma was attributed to Andean uplift, which resulted in the transcontinental connection of the Amazon Riv er while the shift at ~4.5 Ma was associated with either continued uplift or climate change [ Harris and Mix 2002]. To confirm the change in provenances of material reaching the Ceara Rise suggested by Harris and Mix [2002], the detrital silicate fractio n was separated from bulk sediment samples from all three sites (925, 926, and 929) and analyzed for Nd and lead ( Pb ) The Nd and Pb isotopic data will help to better constrain when a shift from South American Shield material to one dominated by Andean mat erial occurred, and whether the second shift in the clay mineralogy of Harris and Mix [2002] at ~4.5 Ma was

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80 the result of continued Andean uplift or changes in weathering related to changing climatic conditions. Material and Methods The Ceara Rise is an as eismic ridge located in the western equatorial Atlantic outside of the direct influence of the Amazon Fan [ Curry et al. 1995]. Ocean Drilling 4 1) were sampled at ~0.25 Ma for fossil fish teeth/debris to reconstruct seawater Nd isotopic values from 18 to 2.5 Ma. A total of eight detritral silicate fractions were taken from each site, with three detrital silicate fractions analyzed representing the time period of 16.25 to 11 Ma, and five samples from 7.25 to 2.75 Ma. Age models for the 2.5 to 14 Ma sections of these sites were based on the astro chronologically tuned age model s, while the 14 to 18 Ma interval is based on Shipboard biostratigraphy [ Curry, Shackleton, Richter, et al. 1995]. The age model for the youngest portion of site 925 (2.5 5.0 Ma) is from Tiedemann and Franz [1997], for 5.0 14 Ma at site 925 and 0 14 Ma at site 926 the age models are from Shackleton and Crowhurst [1997]), and Shipboard biostratigraphic age models have been applied to the 14 to 18 Ma interval at all three sites. The ages of biostratigraphic datums at site 929 were adjusted to the astronomically calibrated ages of site 926 for the 0 14 Ma interval. Fossil fish teeth and debris were handpicked from the >125 m size fraction and dissolved in aqua regia, without prior cleaning based on Martin et al. [2010] Additionally, a comparison was made between Nd isotop es recovered from cleaned fossil fish teeth and Fe Mn oxide coatings at site 926 (Figure 4 2). For analysis of

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81 detrital silicate fractions, approximately 1 g of bulk sediment was processed through the sequential extraction procedure of Basak et al. [2011]. The initial step of the process is decarbonation using 1 M Na acetate in 2.7% optima glacial acetic acid (buffered to pH=5). Fe Mn oxide coatings were removed from the bulk sediment using Chelex cleaned 0.02 N Hydroxylamine Hydrochloride (HH) in 25% aceti c acid solution. A fraction (0.05 g) of the remaining detrital silicate material was heated to >100C for 48 hours in a 4:1 mixture of concentrated optima grade HF:HNO 3 for dissolution. Bulk rare earth elements (REEs) from the fossil fish teeth/debris, the HH fraction, and the detrital silicates were separated on primary quartz columns using Mitsubishi cation exchange resin [ Scher and Martin 2004], or Teflon columns using Eichrom TRUspec TM Resin. Both used optima grade HCl as the eluent. Nd was isolated f rom the bulk REEs using Eichrom LNspec TM resin with HCl as the eluent in volumetrically calibrated Teflon columns [ Pin and Zalduegi 1997]. The total Nd blank for both techniques is 14 pg. Nd and Pb isotopic ratios were measured on a Nu Plasma Multi collec tor Inductively Coupled Plasma Mass Spectrometer (MC ICP MS) using a DSN1000 nebulizer at the University of Florida. The JNdi 1 standard was run between every 4 to 6 unknown samples. Dilutions of the samples were adjusted to achieve a 2 to 6 V beam for 142 Nd. All of the JNdi 1 values analyzed during a given day were averaged and compared to the published value of JNdi 1 (0.512115 0.000007) [ Tanaka et al. 2000] to determine the amount of correction to apply to unknown samples analyzed that day. A drift co rrection was not applied to the data because variations throughout a day of analysis did not indicate a consistent ICP MS based on the variability of normalized JNdi 1 analyzed over the past several years is

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82 Nd Nd represents the deviation in parts per 10 4 of the 143 Nd/ 144 Nd ratio of the s ample relative to the chondritic uniform reservoir with 143 Nd/ 144 Nd=0.512638 [ Jacobsen and Wasserburg 1980]). For Pb analyses, a Tl normalization technique was used following Kamenov et al. [2004]. The Pb concentrates collected from the Pb columns were di ssolved with Tl spiked 2% O ptima grade HNO 3 and the dilutions were adjusted to obtain a 2 5 V beam on 208 Pb. The NBS 981 standard was used and has long term average values over several years of analyses at UF of 206 Pb/ 204 Pb=16.937 207 Pb/ 204 208 Pb/ 204 Results From 18 to 8 Ma, the seawater Nd isotopic values recorded using fossil fish teeth for the two shallowest sites (925 and 926) yield very similar records with values rang ing between 14 to 18 and a general decreasing trend from 18 to 14 Ma followed by an increasing trend from 14 to 8 Ma (Figure 4 3 ; Table 4 1 ) In contrast, there are higher seawater Nd values ( 12 to 14) and less variability at the deepest site (929) (F igure 4 3) At 8 Ma, seawater Nd values increase rapidly to a peak at ~ 11.5 at all three site s ( Figure 4 3) Values for all three sites are similar for the remainder of the record. They decrease gradually from Nd values of ~ 11.5 to ~ 13 between 8 to 4 .5 Ma (Figure 4 3), exhibit a small, but rapid increase to ~ 11 at 4.5 Ma, and stay arou n d t hat value until 2.5 Ma (Figure 4 3) The detrital silicate fraction is less radiogenic than the seawater from 16.5 to 11 Ma with values ranging from 17.2 to 18.7 at Site s 925 and 926, and 16.8 to 17.7 at Site 929 such that there is a greater separation between seawater and silicate values at site 929 (Figure 4 4 ; Table 4 2 ) In the younger section of the record (2.75 to 7.25

PAGE 83

83 Ma), silicate values are more radiog enic ( 11.2 to 13.4) and the y are very similar to seawater values (Figure 4 4) The Pb isotopic values of the detrital silicate fractions are more radiogenic than seawater Pb isotopic values at all three sites for the entire record (Figure 4 5 ; Table 4 3 and 4 4 ) The most radiogenic portion of the curve for both archives occurs in the older interval (11 to 16.5 Ma) with isotopic values of 19.43 to 19.57 ( 206 Pb/ 204 Pb), 15.856 to 15.865 ( 207 Pb/ 204 Pb), and 39.73 to 39.80 ( 208 Pb/ 204 Pb) for the detrital silic ate s from all three sites and values of 19.22 to 19.13 ( 206 Pb/ 204 Pb), 15.748to 15.765 ( 207 Pb/ 204 Pb), 39.31 to 39.37 ( 208 Pb/ 204 Pb) for seawater (Figure 4 5). F or the younger interval detrital values range from 19.01 to 19.08 ( 206 Pb/ 204 Pb), 15.701to 15.719 ( 207 Pb/ 204 Pb), 39.14 to 39.28( 208 Pb/ 204 Pb) while seawater values range between 18.87 to 18.92 ( 206 Pb/ 204 Pb), 15.683 to 15.695 ( 207 Pb/ 204 Pb), 38.94 to 38.99 ( 208 Pb/ 204 Pb) (Figure 4 5) Discussion The Seawater Signature The seawater Nd isotopic composition at all three Ceara Rise sites was less radiogenic than published data from any other deep water site in the Miocene, (Figure 4 3). At ~8 Ma, the Nd isotopic composition at all three sites shifted to values that are more similar to typical values reported from Fe Mn crusts and fish teeth from the deep Atlantic [ Burton et al. 1997; 1998; Palmer and Elderfield 1986; Reynolds et al. 1999; Frank et al. 2003; Thomas and Via 2007]. Although the values younger than ~8 Ma plot within the range of published Atlantic values, the nonradiogenic value s in t h e older section suggest the seawater isotopic composition in the Ceara Rise region is being altered either through b oundary e xchange or r eversible s cavenging as a result of its proximity to Amazon outflow.

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84 Alteration of the seawater Nd isotopic composition toward values of the sediment has been observed along ocean margins in the modern oceans, and the process of this b oundary e Lacan and Jeandel 2005]. Boun dar y exchange occurs as a water mass flows over sediment rich continental margins and interacts with the sediment composed of weathered continental detritus as well as volcanic and authigenic material [ Lacan and Jeandel 2001, 2005a, 2005b ; Tachikawa et al., 2004 ] T hese interactions alter the isotopic composition without increasing the concentration of Nd in seawater [ Lacan and Jeandel 2005]. Lacan and Jeandel [2005] acknowledge the mechanisms which drive the process of boundary exchange remains unclear. Bo undary exchange is unlikely to be the cause of the anomalous seawater Nd isotopic values at Ceara Rise since this process typically occurs at shallow depths on the continental margin where there is abundant continentally derived sediment. Ceara Rise receiv es some material from the Amazon, but the sites receive typical deep sea sediments with carbonate percentages between 50 to 80% except at the deepest site (929) [ King et al ., 1997] which probably reflects dissolution below the lysocline rather than more in put. In addition, there is no known mechanism to bring seawater altered on the margin to depth because deep water masses are not forming in this region. Also, the differences in c arbonate contents suggest that S ite 929 should be the most susceptible to bou ndary exchange, yet this is the site with the least alteration toward silicate values (Figure 4 4). Reversible scavenging, on the other hand is the process of adsorption of REE onto particulates near the surface of the ocean along with desorption within th e water

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85 column or at the sediment water interface as a result of concentration contrast s between the water and absorbed REE [ Sidall et al. 2008] or dissolution of Fe Mn oxyhydroxides and/or particulates carrying the adsorbed REE to depth (Opal, CaCO 3 dus t) Reversible scavenging has mainly been used to explain why the modern ocean Nd concentrations behave like nutrients with low concentrations in surface waters in the Atlantic and higher concentrations in deep waters in the Pacific despite the fact that the Nd isotopic composition of the seawater does not change systematically with the increase in concentration T [ Goldstein and Hemming 2003; Lacan and Jeandel 2001; Jeandel et al. 1995, 1998; Tachikawa et al. 1999a, 1999b; Bertram and Elderfield 1993]. Siddall et al. [2008] used reversible scavenging to try to explain the radiogenic Nd isotopic composition of seawater in the North Pacific at depth, which he attributed to dissolution of highly reactive vo lcanic arc material at the surface of the ocean The released REE s w ere then adsorbed onto particu lates (suggested as dust or opal) that sank carrying the REE to depths w h ere the particulates and/or material carrying Nd down to depth have a tendency to dis solve [ Siddall et al. 2008] Arsouze et al. [2009] also found it necessary to include vertical cycling (reversible scavenging) in models to reconstruct modern Nd concentration and isotopic distribution in seawater. Reversible scavenging appears to be a be tter explanation for Ceara Rise since there appears to be a depth discrepancy with the alteration being the strongest at the t wo shallow sites (925 and 926). Although the potential for reversible scavenging would appear to be high near a large river system such as the Amazon, Albarde et al. [ 1998 ] and [ 1998 ] documented that Nd isotopes behaved conservatively in the Indian Ocean which

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86 receives a large amount of terrigenous material from Ganges and Brahmaputra Rivers. Specifically, there is no Himalayan Nd signature in the seawater records collected from Indian Ocean Fe Mn nodules and crusts, even though [1998] showed that Pb isotopes from the same Fe Mn crusts recorded Himalayan input The discrepancy between the behavior of Pb and Nd isotopes in the Indian O cean may be attributed to trapping of Nd in the Bengal Fan [ 1998 ] or estuaries [ Frank, 2002] or was the result the long residence time of Nd versus Pb On the other hand, Bayon et al. [2004] showed that preformed oxides and oxyhydroxides adsorbed onto sediment reaching the Atlantic via the Congo River altered the seawater Nd isotopic values through reversible scavenging, and in turn showed that Nd behaved non conservatively near a large input of terrigeno us material. All three sites along the Ceara Rise received the same terrigenous material based on the Nd and Pb isotopic composition of the detrital silicate fraction (Figure 4 4 and 4 5), but the amount of terrigenous material reaching each of the sites is controlled by their proximity to the Amazon Fan and water depth [ King et al. 1997]. King et al. [1997] showed that site 925 receives the most terrigenous material followed by site 929, while site 926 receives the least terrigenous material of the three sites. Yet, despite the fact that sites 925 and 926 receive different amounts of terrigenous material, these two shallow sites appear to be the most strongly affected by weathering inputs from the Amazon River. This depth discrepancy is consistent with re versible scavenging, where most of the desorption of Nd into the seawater as a result of dissolution or concentration differences between the seawater and adsorbed Nd appears to have occurred closer to the depth of the two shallower sites. Site 929 was wel l below the lysocline and the

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87 sediments accumulation prior to 5.7 Ma at this site are described as red clay [ King et al. 1997]). Therefore, the seawater Nd isotopic composition at Site 929 would be less impacted by reversible scavenging that occurred at a shallower depth. In summary, the proximal location of Ceara Rise to the Amazon has resulted in alteration of the seawater Nd isotopic composition in this region, presumably through reversible scavenging. Unlike most deep sea sites, the sites at Ceara Ris e are located close enough to a major source of continental detrital input to be impacted by sediment from that source. In addition, the detrital material includes highly reactive Fe oxide coatings that are common byproducts of tropical weathering. The n et result appears to be that seawater Nd isotopes in this region have been altered by interaction with this sediment. Thus, seawater Nd isotopes in this specific region do not reflect the composition of the water mass advected into the region and cannot b e used to track the boundary between AABW and NCW. Interpretation of Detrital Isotopes The modern Amazon River drains the Andes and the lowlands of Brazil, which is composed of the Brazil and Guyana cratons, and ultimately flowing into the Atlantic forming the Amazon Fan. The sediment reaching the Amazon Fan today is dominantly sourced from the Andean highlands [ Gibbs 1967; Milliman 1979; Damuth et al. 1988; McDaniel et al. 1997; Dobson et al. 1997; Dobson et al. 2001]. Estimates for the timing of ini tiation of a dominant Andean source, and development of the Amazon River and Fan range from the m iddle/ l ate Miocene to the end of the Pliocene [ Castro et al., 1978; Campbell, 1992; Hoorn, 1993; Hoorn 1994; Hoorn et al. 1995; Campbell et al. 2006; Figuei redo et al. 2009, 2010; Campbell 2010; Hoorn et al., 2010]. Studies indicate that the continental shelf underlying the Amazon Fan was a carbonate platform

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88 that only received moderate amounts of Amazon River sediment until the late Miocene. Figueiredo et al. [2009] showed that during the early to middle Miocene the sediment reaching the Amazon shelf was derived from the lowland cratons, but from the late Miocene to present the sediment w as predominantly derived from the Andes which they attributed to the onset of a transcontinental connection of the Amazon. The timing of this switch and initiation of the fan was initially placed between 11.8 to 11.3 Ma [ Figueiredo et al. 2009], and later adjusted to ~10.5 Ma [ Figueiredo et al. 2010] with a fully develope d Amazon River by ~6.8 Ma [ Figueiredo et al., 2009]. Prior to the transcontinental connection during the late middle Miocene, Hoorn et al. [1995] argue d early Andes uplift altered the northwest Amazonia region generating a proto Amazon River which flowed n orth instead of flowing east to the Atlantic until continued Andes uplift in the late Miocene created the modern Amazon drainage basin complete with a transcontinental connection. Harris and Mix [2002] used the ratio of chlorite/kaolinite to determine whet her the Ceara Rise was receiving physically weathered material from the Andean Highlands (chlorite) or the chemically weathered material from the Amazon Lowlands (kaolinite). Prior to 8 Ma, the chlorite/kaolin i te ratio was low, suggesting a lack of materia l sourced from the Andean region. After 8 Ma, the chlorite/kaolinite ratio increased along with a notable increase in terrigenous mass accumulation rates as a result of an increase in the supply of Andean sourced sediments. Another noted shift in the chlor ite/kaolinite record occurred at ~4.5 Ma, which Harris and Mix [2002] interpreted as additional input of Andean derived sediment in response to another Andean uplift event, but they could not rule out a change in paleoclimate as the cause for this observed shift. The timing of

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89 the second chlorite/kaolin i te shift was also accompanied by an increase in terrigenous mass accumulation rates and Harris and Mix [2002] argued the two events could be correlated with two Andean tectonic events : Quecha 2 and 3 which are well known from the Peruvian Andes [ Megard et al. 1984]) and have been credited with the development of the transcontinental Amazon connection [ Harris and Mix 2002]. The findings of Harris and Mix [2002] were similar to the findings of Dobson et al. [2001] who looked at the terrigenous mass accumulation rates of the material reaching Ceara Rise and the geochemical composition of the terrigenous material. Dobson et al. [200 1] noted that the composition of Ceara Rise changed from shield material to sed iment predominately sourced from the Andes at ~10 Ma which coincided with an increase in the terrigenous mass accumulation rate at Ceara Rise. The Pb isotopic compositions of the d etrital silicates provide additional evidence to support this shie ld to Andes source transition. Pb isotope cross plots illustrate that the 11 to 16.5 Ma silicates from all three Ceara Rise sites plot near the field of Older Cratonic Rock while on v alues for the younger silicates (2.75 Ma to 7.25 Ma) are clearly distinct and plot within the Amazon Delta and Amazon Fan mud fields of McDaniel et al. [1997] (Figure 4 6) as defined by Pleistocene to modern sediment The shift observed in the Pb isotopic composition of the detrital silicate fraction further demonstrates that the se diment reaching the Ceara Rise in the older section was sourced from the Amazon lowland s (South American S hield material) while the sediment reaching the Ceara Rise during the y ounger section of the record was sourced from the Andean highland s (volcanic a rc material)

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90 The Nd isotopic data also support a shift from detrital silicates sourced from the South American Shield material, Nd value of ~ 20 [ Allegre et al. 1996], during the older section (16.5 to 11 Ma) to more radiogenic values in the younger section (7.25 to 2.75 Ma) with values slightly less radiogenic than Amazon Fan Pleistocene silicate values until ~4.5 Ma w hen they become slightly more radiogenic and overlap with the Nd isotopic values of the Amazon Fan silicate values of McDaniel et al. [1997]. Although the detrital silicate data set is relatively low resolution, the changes appear t o track the variations i n values recorded in the record from fish teeth, which provides better constraint on the exact timing. These data argue for a large shift at ~8 Ma, a nd a smaller shift at ~4.5 Ma, which agrees well with observed shifts in the clay mineralogy at Ceara Rise [ Harris and Mix, 2002], and supports their conclusion that the shift is generated by tectonic events in the Andes and changes in the Amazon drainage basin rather than climate controlled weathering. Summary Miocene seawater Nd and Pb isotopes preserved in fossil fish teeth/debris at Ceara Rise record similar patterns of change as the detrital silicate fractio ns Therefore, the observed shifts appear to be driven by local weathering inputs from the Amazon River that are transmitted into the seawater thro ugh reversible scavenging and reflect major changes in the provenance of the source material. The impact of reversible scavenging has been documented in the Pacific, but appears to be less common in the Atlantic; however, the large amount of sediment trans ported down the Amazon R iver that reaches the Ceara Rise is unusual for a deep sea location Overprinting of seawater Nd isotopic values by weathering inputs prevented reconstruction of circulation to identify shifts in the boundary between NCW and AABW at Ceara Rise.

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91 The Nd and Pb isotopic composition of the detrital silicate fraction recorded a dramatic shift at ~8 Ma. Prior to 8 Ma the nonradiogenic Nd isotopic values and radiogenic Pb isotopic values are similar to South American cratonic shield materia l. These results suggest the detrital silicate material reaching Ceara Rise was sourced from the Amazon lowlands which appear to dominate the Amazon drain age basin at this time. After 8 Ma, the Nd isotopic values shift to more radiogenic values and Pb iso topic values shift to less radiogenic values both of which are more representative of volcanic arc or Andean material. The timing of the observed shift s in the Pb and Nd isotop es agrees with shifts in the mineralogy and geochemical data of the silicate ma terial reaching Ceara Rise and has been linked to the development of a transcontinental connection of the Amazon River and an overall change in the Amazonian drainage basin following Andean tectonic events After this connection the Amazon lowland (South A merican shield) material was overwhelmed by younger Andean highland material (volcanic arc) consistent with modern and Pleistocene detrital sources in the Amazon River and on the Amazon Fan.

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92 Figure 4 1. Bathymetric map of the Atlantic Oce an [ Schlitzer, R., 2010], and the bathymetric profile illustrating the position of Ocean Drilling Program sites 925, 926, 929 [modified from Curry et al., 1995].

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93 Figure 4 2. Salinity profile along a north south transect in the Atlantic overlain by s Nd profiles illustrating that Nd isotopes are also a conservative tracker of water mass in the Atlantic. The gray rectangle outlines the location and depths of sites on Ceara Rise [modified from von Blackenburg, 1999].

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94 Figure 4 Nd from fossil fish teeth vs. age for sites 925, 926, and 929 on Ceara Rise in the western equatorial Atlantic. The gray shadow box represents the Nd values for the Atlantic [Burton et al., 1997, 1999; Ling Thomas and Via, 2007]. The Nd isotopic values for the Ceara Rise sites plot well below these values from 18 to 8 Ma, and in the lower portion of the field after 8 Ma.

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95 Figure 4 Nd vs. age for detrital silicate fractions (stars) and fossil fish teeth (lines) for sites 925, 926, and 929 on Ceara Rise. The detrital silicate fractions are less radiogenic than seawater values from 16.5 to 11 Ma, with the largest offset o bserved at the deepest site (929). From 7.25 to 2.75 Ma, the detrital silicate fraction and seawater values record similar values for all three sites, with no consistent offset observed.

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96 Figure 4 5. 206 Pb/ 204 Pb vs. age for both detrital silicate fractions (circles) and Fe Mn oxide coatings, which are interpreted to represent seawater values (squares) for sites 925, 926, and 929 on Ceara Rise. Seawater values remain less radiogenic than detrital silicate fractions for the entire record, an d both archives show a shift from radiogenic to less radiogenic values between the older section (16.5 to 11 Ma) and the younger section (7.25 to 2.75 Ma).

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97 Figure 4 6. Pb isotopic crossplots of a) 207 Pb/ 204 Pb vs. 206 Pb/ 204 Pb, and b) 208 Pb/ 204 Pb vs. 206 Pb/ 204 Pb for the detrital silicate fractions from all three Ceara Rise sites (925, 926, and 929) illustrating that older detrital silicate fractions (16.5 to 11 Ma; open symbols ) plot close to the Old Cratonic Rock Field, while younger detrital silicate fr actions (7.25 to 2.75 Ma; filled symbols ) plot within the Pleistocene Amazon Fan sediment and just outside the Andean Igneous Rocks field. Shaded zones and reference arrows ( which indicate the direction of published data for older cratonic rocks from South America) from McDaniel et al. [1997; and references therein].

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98 Table 4 1. Nd isotopic results for Ceara Rise fossil fish teeth Sample Depth (mcd) Age (Ma) 143 Nd/ 144 Nd a Nd(0) b 154 925C 9H 4, W, 6 8 84.14 2.50 0.512085 10.78 154 925D 10H 2, W, 118 120 100.14 3.00 0.512064 11.20 154 925C 11H 3, W, 87 89 108.21 3.25 0.512053 11.41 154 925D 11H 6, W, 99 101 116.23 3.50 0.512099 10.52 154 925D 12H 5, W, 32 34 12 4.26 3.75 0.512036 11.75 154 925C 13H 2, W, 142 144 128.98 4.00 0.512076 10.97 154 925D 13H 5, W, 78 80 135.73 4.25 0.512073 11.02 154 925D 14H 3, W, 102 104 142.42 4.50 0.512022 12.02 154 925C 15H 2, W, 115 117 149.16 4.75 0.511968 13.06 154 925D 15H 4, W, 107 109 155.80 5.00 0.511957 13.28 154 925D 16H 3, W, 3 5 162.54 5.25 0.511977 12.90 154 925C 17H 2, W, 81 83 169.21 5.50 0.511982 12.79 154 925C 18H 4, W, 87 89 182.56 6.00 0.512009 12.26 154 925B 19H 4, W, 132 134 189.12 6.25 0.511999 12.47 154 925C 19H 5, W, 119 121 195.62 6.50 0.512015 12.15 154 925C 20H 3, W, 62 64 202.22 6.75 0.511997 12.50 154 925D 20H 3, W, 109 111 208.78 7.00 0.511981 12.82 154 925C 21H 5, W, 13 15 215.34 7.25 0.512038 11.70 154 925 D 21H 5, W, 100 102 221.90 7.50 0.512042 11.63 154 925D 22H 3, W, 25 27 228.27 7.74 0.512028 11.90 154 925B 23H 5, W, 52 54 234.99 8.00 0.511999 12.46 154 925C 23H 5, W, 142 144 241.57 8.25 0.511884 14.71 154 925D 24H 3, W, 111 113 249.12 8.54 0.511905 14.29 154 925C 25H 4, W, 19 21 254.70 8.75 0.511891 14.56 154 925D 25H 4, W, 127 129 261.26 9.00 0.511953 13.35 154 925D 26H 2, W, 30 32 267.81 9.25 0.511865 15.08 154 925D 26H 6, W, 28 30 273.79 9.50 0.511825 15.86 154 925D 2 7H 4, W, 1 3 278.93 9.75 0.511861 15.16 154 925B 28H 3, W, 119 121 284.02 10.00 0.511915 14.11 154 925B 29H 2, W, 32 34 294.22 10.50 0.511934 13.73 154 925D 29H 4, W, 80 82 304.42 11.00 0.511821 15.94 154 925B 30H 4, W, 98 100 309.56 11.25 0.511849 15.38 154 925D 30H 5, W, 0 2 314.89 11.50 0.511840 15.57 154 925C 31H 2, W, 75 77 324.92 12.25 0.511836 15.64 154 925B 32H 2, W, 33 35 328.25 12.50 0.511795 16.44 154 925B 32H 4, W, 63 65 331.51 12.74 0.511765 17.02 154 925D 32H 3, W, 109 111 334.95 13.00 0.511767 16.99 154 925D 32H 5, W, 147 149 338.29 13.25 0.511791 16.51 154 925B 33H 4, W, 17 19 341.63 13.50 0.511776 16.81 154 925D 33H 3, W, 46 48 344.98 13.75 0.511908 14.23 154 925D 33H 5, W, 80 82 348.31 14.00 0.511725 17.81 154 925B 34H 1, W, 97 99 351.57 14.24 0.511823 15.89

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99 Table 4 1. Continued Sample Depth (mcd) Age (Ma) 143 Nd/ 144 Nd a Nd(0) b 154 925B 34H 3, W, 142 144 355.03 14.50 0.511883 14.72 154 925A 5R 5, W, 61 63 368.41 15.50 0.51186 9 15.00 154 925C 36X 3, W, 28 30 371.72 15.75 0.511845 15.47 154 925D 36H 1, W, 77 79 376.71 16.00 0.511873 14.92 154 925A 7R 3, W, 15 17 384.19 16.25 0.511878 14.83 154 925A 8R 1, W, 98 100 391.69 16.50 0.511921 13.99 154 925C 38X 2, W, 21 23 399.21 16.75 0.511860 15.17 154 925A 9R 5, W, 32 34 406.72 17.00 0.511768 16.96 154 925A 10R 2, W, 100 102 412.58 17.20 0.511931 13.78 154 925A 11R 2, W, 63 65 421.77 17.50 0.511780 16.74 154 925A 12R 1, W, 13 15 429.25 17.75 0.511791 16.52 154 926C 8H 3, W, 131 133 77.83 2.48 0.512003 12.39 154 926A 10H 3, W, 18 20 93.69 3.00 0.512079 10.91 154 926C 10H 4, W, 44 46 99.75 3.20 0.512068 11.12 154 926C 11H 5, W, 59 61 112.56 3.62 0.512094 10.61 154 926C 13H 3, W, 49 51 132.95 4.28 0.512079 10.91 154 926C 15H 1, W, 41 43 140.43 4.50 0.511992 12.61 154 926B 15H 5, W, 54 56 153.88 4.99 0.511953 13.36 154 926C 15H 4, W, 67 69 156.11 5.10 0.511969 13.04 154 926A 16H 3, W, 44 46 158.39 5.20 0.511989 12.65 154 926A 16H 6, W, 34 36 162.79 5.40 0.511961 13.20 154 926C 16H 3, W, 22 24 164.87 5.50 0.511967 13.08 154 926C 16H 4, W, 92 94 167.07 5.60 0.512009 12.26 154 926C 16H 6, W, 2 4 169.17 5.69 0.511995 12.54 154 926B 17H 2, W, 104 106 171.5 0 5.80 0.512005 12.34 154 926B 17H 4, W, 44 46 173.90 5.87 0.512006 12.32 154 926C 17H 3, W, 67 69 175.89 5.99 0.511999 12.46 154 926C 17H 5, W, 147 149 179.69 6.21 0.512013 12.19 154 926B 18H 3, W, 114 116 183.19 6.41 0.512004 12.36 154 926B 19H 4, W, 94 96 195.28 7.11 0.512061 11.25 154 926B 19H 6, W, 14 16 197.48 7.23 0.512046 11.54 154 926A 20H 3, W, 5 7 200.03 7.38 0.512077 10.94 154 926B 20H 3, W, 104 106 204.73 7.69 0.512044 11.58 154 926A 21H 3, W, 75.5 80 210.80 7.98 0.511859 15.20 154 926B 21H 4, W, 121 126 215.36 8.20 0.511936 13.69 154 926C 22H 2, W, 114 119 219.71 8.41 0.511849 15.39 154 926C 22H 3, W, 117 119 221.22 8.51 0.511888 14.62 154 926C 22H 4, W, 94 99 222.51 8.59 0.511878 14.83 154 926 C 22H 4, W, 97 99 222.52 8.59 0.511846 15.44 154 926B 22H 4, W, 14 16 224.00 8.69 0.511957 13.28 154 926B 22H 5, W, 10.5 16 225.48 8.80 0.511940 13.62 154 926A 23H 1, W, 82.5 88 228.40 8.99 0.511924 13.93

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100 Table 4 1. Continued Sample Dept h (mcd) Age (Ma) 143 Nd/ 144 Nd a Nd(0) b 154 926A 23H 1, W, 88 90 228.44 9.00 0.511889 14.60 154 926A 23H 3, W, 73.5 79.5 231.32 9.19 0.511875 14.88 154 926B 23H 3, W, 10.5 16 234.19 9.39 0.511868 15.02 154 926B 23H 5, W, 0 6 237.09 9.58 0.511890 14.59 154 926A 24H 2, W, 14 1 146 240.53 9.82 0.511914 14.12 154 926A 24H 4, W, 131 136 243.43 10.00 0.511917 14.06 154 926B 24H 4, W, 11 16 246.15 10.22 0.511856 15.25 154 926B 24H 5, W, 69.5 76 248.23 10.38 0.511844 15.49 154 926A 25H 3, W, 0 6 251.37 10.63 0.511903 14.34 154 926A 25H 4, W, 81 86 253.68 10.81 0.511884 14.71 154 926B 25H 4, W, 124 129 257.27 11.10 0.511847 15.43 154 926B 25H 5, W, 129 135 258.82 11.22 0.511866 15.06 154 926A 26H 1, W, 110 116 261.48 11.43 0.511869 15.00 154 926A 26H 3, W, 51 56 263.89 11.62 0.511857 15.23 154 926B 26H 4, W, 120 125.5 268.99 12.00 0.511870 14.98 154 926B 27H 3, W, 31 36 277.39 12.58 0.511795 16.44 154 926B 27H 5, W, 61 65 280.68 12.80 0.511787 16.60 154 926A 28H 3, W, 131.5 136 284.52 13.0 2 0.511789 16.56 154 926A 28H 5, W, 90 96 287.11 13.16 0.511803 16.29 154 926B 29H 2, W, 89 93 290.62 13.35 0.511812 16.11 154 926B 29H 5, W, 38 43 294.61 13.57 0.511789 16.57 154 926B 29H 7, W, 29 34 297.53 13.73 0.511792 16.50 154 926B 30 X 4, W, 100 102 303.34 14.00 0.511945 13.51 154 926B 30X 6, W, 74 76 306.08 14.25 0.511808 16.18 154 926B 31X 1, W, 127 129 308.82 14.50 0.511803 16.29 154 926B 31X 3, W, 92 94 311.47 14.74 0.511846 15.45 154 926B 31X 5, W, 71 73 314.27 1 5.00 0.511834 15.68 154 926B 31X 7, W, 42 44 316.98 15.25 0.511888 14.63 154 926B 32X 2, W, 97 99 319.73 15.50 0.511830 15.75 154 926B 32X 6, W, 42 44 325.19 16.00 0.511952 13.38 154 926B 33X 1, W, 105 107 327.93 16.25 0.511815 16.06 154 926B 33X 5, W, 51 53 333.40 16.75 0.511963 13.16 154 926B 34X 4, W, 5 7 341.15 17.46 0.511953 13.35 154 926B 34X CC, W, 25 27 345.88 17.89 0.511846 15.45 154 926B 35X 1, W, 85 87 347.06 18.00 0.511850 15.37 154 929A 9H 1, W, 104 106 80.82 2.50 0.512086 10.76 154 929C 9H 3, W, 38 40 87.93 2.75 0.512065 11.17 154 929A 10H 4, W, 41 43 94.89 3.00 0.512088 10.73 154 929A 11H 2, W, 41 43 101.99 3.25 0.512074 10.99 154 929C 11H 4, W, 33 35 109.05 3.50 0.512085 10.78 154 929A 12H 4, W, 125 127 116.12 3.75 0.512076 10.96 154 929C 12H 5, W, 133 135 121.24 4.00 0.512107 10.36

PAGE 101

101 Table 4 1. Continued Sample Depth (mcd) Age (Ma) 143 Nd/ 144 Nd a Nd(0) b 154 929A 13H 4, W, 97 99 126.32 4.25 0.512105 10.39 154 929C 13H 4, W, 133 135 131.32 4.50 0.512011 12.22 154 929A 15H 6, W, 15 17 144.37 5.25 0.511980 12.84 154 929A 16X 1, W, 62 64 146.84 5.49 0.512007 12.31 154 929C 15X 4, W, 15 17 149.47 5.75 0.511987 12.70 154 929C 16X 5, W, 102 104 160.99 6.25 0.512 024 11.97 154 929B 18X 2, W, 117 119 174.78 6.75 0.512010 12.24 154 929B 19X 5, W, 6 8 188.59 7.25 0.512082 10.84 154 929A 21X 2, W, 61 63 202.37 7.75 0.511960 13.22 154 929B 21X 6, W, 54 56 209.27 8.00 0.511961 13.20 154 929A 22X 5, W, 50 5 2 216.15 8.25 0.511985 12.74 154 929A 23X 1, W, 112 114 220.63 9.50 0.511970 13.03 154 929A 23X 3, W, 66 68 223.17 10.24 0.511964 13.14 154 929A 23X 4, W, 89 91 224.90 10.75 0.511971 13.00 154 929A 23X 5, W, 26 28 225.77 11.01 0.511951 13.4 0 154 929A 23X 5, W, 109 111 226.60 11.25 0.511996 12.52 154 929A 23X 6, W, 46 48 227.47 11.51 0.511987 12.70 154 929A 23X 6, W, 129 131 228.30 11.75 0.511992 12.59 154 929A 24X 1, W, 32 34 229.13 11.99 0.511937 13.67 154 929A 24X 1, W, 11 7 119 229.98 12.24 0.511955 13.32 154 929A 24X 2, W, 57 59 230.88 12.51 0.511949 13.44 154 929A 24X 2, W, 139 141 231.70 12.75 0.511994 12.55 154 929A 24X 4, W, 9 11 233.40 13.25 0.511945 13.51 154 929A 24X 4, W, 92 94 234.23 13.49 0.511976 12.91 154 929A 24X 5, W, 28 30 235.09 13.75 0.511957 13.28 154 929A 24X 5, W, 109 111 235.90 13.98 0.511928 13.84 154 929A 24X 6, W, 49 51 236.80 14.25 0.511938 13.65 154 929B 24X 5, W, 110 112 237.63 14.49 0.512011 12.22 154 929B 24X 6, W, 130 132 239.34 15.00 0.512012 12.21 154 929A 25X 1, W, 77 79 240.20 15.25 0.511947 13.47 154 929A 25X 2, W, 12 14 241.05 15.50 0.511976 12.91 154 929A 25X 2, W, 100 102 241.93 15.76 0.511969 13.04 154 929A 25X 4, W, 0 2 243.93 16.00 0.5 11957 13.28 154 929A 26X 2, W, 32 34 250.85 16.75 0.512013 12.18 154 929A 26X 3, W, 37 39 252.40 16.91 0.511909 14.22 154 929A 26X 5, W, 53 55 255.56 17.25 0.511969 13.04 154 929A 26X 6, W, 80 82 257.33 17.44 0.511987 12.70 154 929A 27X 1 W, 133 135 260.16 17.75 0.512083 10.82 154 929A 27X 3, W, 67 69 262.50 18.00 0.511942 13.57 a 143 Nd/ 144 Nd values analyzed on a given day were corrected by the difference between the average JNdi 1 value for that day and Tanaka et al. [ 2000]. b Nd(0) = [ 143 Nd/ 144 Nd (sample) / 143 Nd/ 144 Nd (CHUR) 1] 10 4 where 143 Nd/ 144 Nd (CHUR) = 0.512638. Nd units.

PAGE 102

102 Table 4 2 Nd isotopic values for detrital silicates Sample Depth (mcd) Age (Ma) 143 Nd/ 144 Nd Nd 154 925B 10H 4W 130 131 92.10 2.75 0.512025 12.0 154 925D 13H 5W 76 77 136.21 4.27 0.512031 11.8 154 925C 15H 2W 117 118 149.18 4.75 0.511961 13.2 154 925C 17H 2W 83 84 169.23 5.50 0.511999 12.5 154 925C 21H 5W 16 17 215.37 7.25 0.511951 13.4 154 925D 29H 4W 79 80 304.39 11.00 0.511728 17.8 154 925D 32H 5 W 149 150 338.30 13.25 0.511698 18.3 154 925A 7R 3W 14 15 384.17 16.25 0.511749 17.3 154 926C 29H 2W 32 33 86.28 2.76 0.512029 11.9 154 926C 13H 3W 47 49 132.93 4.28 0 .512052 11.4 154 926C 14H 3W 13 14 143.31 4.62 0.511980 12.8 154 926C 16H 3W 21 23 164.86 5.50 0.511975 12.9 154 926B 25H 4W 122 123 257.24 11.09 0.511755 17.2 154 926B 29X 2W 88 89 290.59 13.35 0.511711 18.1 154 926B 33X 1W 107 108 327.94 16 .25 0.511679 18.7 154 929C 9H 3W 36 38 87.91 2.75 11.946052 11.9 154 929A 13H 4W 95 97 126.30 4.25 11.258293 11.3 154 929C 13H 4W 131 133 131.30 4.50 12.292160 12.3 154 929A 16X 1W 61 62 146.83 5.49 12.019063 12.0 154 929A 19X 2W 8 5 86 181.66 7.00 12.916383 12.9 154 929A 23X 5W 24 26 225.75 11.00 17.660285 17.7 154 929A 24X 4W 8 9 233.39 13.25 17.422486 17.4 154 929A 25X 7W 10 11 248.53 16.50 16.759250 16.8

PAGE 103

103 Table 4 3 Pb isotopic values for detrital silicates Sample Depth (mcd) Age (Ma) 208 Pb/ 204 Pb 207 Pb/ 204 Pb 206 Pb/ 204 Pb 154 925B 10H 4W 130 131 92.10 2.75 39.172 15.704 19.083 154 925D 13H 5W 76 77 136.21 4.27 39.144 15.701 19.026 154 925C 15H 2W 117 118 149.18 4.75 39.241 15.715 19.017 154 925C 17H 2W 83 84 169.23 5.50 39.208 15.711 19.011 154 925C 21H 5W 16 17 215.37 7.25 39.282 15.720 19.052 154 925D 29H 4W 79 80 304.39 11.00 39.726 15.858 19.428 154 925D 32H 5W 149 150 338.30 13.25 39.790 15.865 19.573 154 925A 7R 3W 14 15 384. 17 16.25 39.802 15.856 19.557 154 926C 29H 2W 32 33 86.28 2.76 39.199 15.715 19.114 154 926C 13H 3W 47 49 132.93 4.28 39.180 15.704 19.040 154 926C 14H 3W 13 14 143.31 4.62 39.159 15.697 18.905 154 926C 16H 3W 21 23 164.86 5.50 39.262 15.722 19.032 154 926B 19H 4W 94 96 195.28 7.11 39.200 15.712 19.012 154 926B 25H 4 W 122 123 257.24 11.09 39.591 15.824 19.358 154 926B 29X 2W 88 89 290.59 13.35 39.794 15.864 19.585 154 926B 33X 1 W 107 108 327.94 16.25 39.877 15.884 19.660 154 92 9C 9H 3W 36 38 87.91 2.75 39.247 15.717 19.144 154 929A 13H 4W 95 97 126.30 4.25 39.230 15.712 19.096 154 929C 13H 4W 131 133 131.30 4.50 39.248 15.709 19.010 154 929A 16X 1W 61 62 146.83 5.49 39.252 15.719 19.010 154 929A 19X 2W 85 86 181.66 7. 00 39.259 15.722 19.067 154 929A 23X 5W 24 26 225.75 11.00 39.599 15.825 19.419 154 929A 24X 4W 8 9 233.39 13.25 39.722 15.844 19.546 154 929A 25X 7W 10 11 248.53 16.50 39.889 15.872 19.690

PAGE 104

104 Table 4 4. Pb isotopic values for leachates Sample Depth (mcd) Age (Ma) 208 Pb/ 204 Pb 207 Pb/ 204 Pb 206 Pb/ 204 Pb 154 925B 10H 4W 130 131 92.10 2.75 38.955 15.683 18.911 154 925D 13H 5W 76 77 136.21 4.27 38.957 15.685 18.901 154 925C 15H 2W 117 118 149.18 4.75 38.990 15.695 18.925 154 925C 17H 2W 83 84 169. 23 5.50 38.941 15.686 18.866 154 925C 21H 5W 16 17 215.37 7.25 39.003 15.692 18.901 154 925D 29H 4W 79 80 304.39 11.00 39.313 15.748 19.144 154 925D 32H 5W 149 150 338.30 13.25 39.374 15.765 19.223 154 925A 7R 3W 14 15 384.17 16.25 39.323 15.758 19.131 154 926C 29H 2W 32 33 86.28 2.76 38.995 15.685 18.935 154 926C 13H 3W 47 49 132.93 4.28 38.953 15.677 18.871 154 926C 14H 3W 13 14 143.31 4.62 38.983 15.680 18.844 154 926C 16H 3W 21 23 164.86 5.50 38.986 15.671 18.894 154 926B 19H 4W 94 96 19 5.28 7.11 38.970 15.688 18.884 154 926B 25H 4W 122 123 257.24 11.09 39.270 15.737 19.108 154 926B 29X 2W 88 89 290.59 13.35 39.284 15.745 19.186 154 926B 33X 1W 107 108 327.94 16.25 39.325 15.758 19.183 154 929C 9H 3W 36 38 87.91 2.75 39.024 15. 685 18.946 154 929A 13H 4W 95 97 126.30 4.25 38.900 15.660 18.913 154 929C 13H 4W 131 133 131.30 4.50 38.997 15.663 18.868 154 929A 16X 1 W 61 62 146.83 5.49 39.127 15.695 18.896 154 929A 19X 2W 85 86 181.66 7.00 38.965 15.681 18.908 154 929A 23X 5W 24 26 225.75 11.00 39.196 15.723 19.083 154 929A 24X 4W 8 9 233.39 13.25 39.202 15.725 19.087 154 929A 25X 7W 10 11 248.53 16.50 39.093 15.708 19.015

PAGE 105

105 CHAPTER 5 CONCLUSIONS The results of this study showed that t he neodymium ( Nd ) isotopic values were rep resentative of Pacific Deep Water ( PDW ) and the onset of the carbonate crash in the eastern equatorial Pacific sites and the Caribbean is consistent with a reorganization of the Pacific which resulted in enhanced flow of PDW in the equatorial region Altho ugh many studies suggest closure of the Central American Seaway ( CAS ) played a major role in driving these changes, the timing of events supports climate change in the Southern Ocean and increased Deep Western Boundary Current flow as the primary factors l eading to changes in Miocene Pacific circulation. Although the onset of both the Pacific and Caribbean carbonate crash intervals is attributed to encroachment of PDW, termination of these events has a different cause at each location. Shoaling of the CAS u ltimately created a barrier to flow of corrosive Pacific deep and intermediate waters into the Caribbean Basin and allowed for the recovery from the Caribbean carbonate crash Although equatorial Pacific continued to be exposed to corrosive PDW, the r ecove ry from the Pacific carbonate crash coincides with increased surface water productivity and carbonate deposition The Caribbean Basin was filled with PDW while the CAS was open for exchange from the middle to late Mi ocene. The peak flow of Pacific sourced waters through the CAS occurred over the same time as suggested times of North Atlantic Deep Water (NADW) production, and is in disagreement with most Ocean General Circulation Models. Unfortunately, a n attempt to study NADW production using seawater Nd i sotopes on the Ceara Rise in the tropical western Atlantic was unsuccessful because the Miocene Nd isotopes from fish teeth and Pb isotopes from oxide coatings recorded

PAGE 106

106 seawater values which were strongly altered by detrital outputs from the Amazon River. The sites on the Ceara Rise record shifts in the composition of the detrital silicate fraction rather than shifts in the position in the boundary between NADW and Antarctic Bottom Water. O bserved shifts in the seawater signals indicate the sediment on Cear a Rise records changes in the sediment supply from the Amazon River despite the fact that these sites are located beyond the position of the Amazon Fan. Alteration of the seawater values by the detrital inputs appear to be driven by reversible scavenging a nd the major changes record shifts in the provenance of the source material that can be used to understand the evolution of the Amazon drainage system Prior to ~8 Ma Nd and Pb isotopic composition s of detrital silicate fraction s suggest this material was derived from an Amazon lowlands source. This shift in isotopic values at ~8 Ma documents a shift to detrital silicates dominantly sour ced from the Andean Highlands. The timing of this transition supports previous arguments for the development of a transcon tinental connection to the Andes at that time.

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107 LIST OF REFERENCES Abouchami W., S. L. Goldstein, S. J. G. Galer A. Eisenhauer, and A. Mangini (1997) Secular changes of lead and neodymium in central Pacific seawater recorded by a Fe Mn crust Geochim. C osmochim. Acta 61 (18), 3957 3974. Albar de F., S. L. Goldstein and D. Dautel D. (1997) The neodymium isotopic composition of manganese nodules from the Southern and Indian oceans, the global oceanic neodymium budget, and their bearings on the deep oce an circulation Geochim. Cosmochim. Acta 61 1277 1291. Alpers, C., and G. Brimhall ( 1988 ), Middle Miocene climate change in the Atacama Desert, northern Chile: evidence from supergene mineralization at La Escondida Geol. Soc. Am. Bull., 100 1640 165 6. Arsouze, T., J. C. Dutay, F. Lacan, and C. Jeandel (2009), Reconstructing the Nd oceanic cycle using a coupled dynamical biogeochemical model, Biogeosciences, 6 2829 2846. Basak C., E. E. Martin, G. D. Kamenov ( 2011 ), Seawater Pb isotopes extracte d from Cenozoic marine sediments, Chemical Geology 286 94 108. Bayon G., C. R. German, K. W. Burton, R. W. Nesbitt, and N. Rogers ( 2004 ), Sedimentary Fe Mn oxyhydroxides as paleoceanographic archives and the role of aeolian flux in regulating oceanic dissolved REE, Earth Planet. Sci. Lett. 224 477 492. variable dispersion double focusing plasma mass spectrometer with performance illustrated for Pb isotopes, Inter national Journal of Mass Spectrometry 181 51 58. Bertram C. J., and H. Elderfield (1993) The geochem ical balance of the rare earth elements and Nd isotopes in the oceans Geochim. Cosmochim. Acta 57 1957 1986. Billups, K., A. C. Ravelo, and J. C. Z achos ( 1998 ), Early Pliocene deep water circulation in the western equatorial Atlantic: Implications for high latitude climate change, Paleoceanography 13 84 95 Broecker W. S., and T. H. Peng (1982) Tracers in the Sea Eldigio Press. Buckry D. (19 73) Low latitude coccolith biostratigraphic zonation in Init ial Rep or ts DSDP 15 edited by N. T. Edgar, J. B. Saunders et al. pp. 685 703 U.S. Govt. Printing Office, Washington.

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108 Burton, K. W., H. ntral American Isthmus and its effect on deep water formation in the north Atlantic, Nature 386 382 385, doi: 10.1038/386382a0. Burton, K. W., D. C. Lee, J. N. Christensen, A. N. Halliday, and J. R. Hein (1999), Actual timing of neodymium isotopic va riations recorded by Fe Mn crusts in the western North Atlantic, Earth Planet. Sci. Lett. 171 149 156, doi: 10.1016/S0012 821X(99)00138 7. Campbell K. E. Jr., C. D. Frailey, and L. Romero Pittman (2006), The Pan Amazonian Ucayali Peneplain, late Neog ene sedimentation in Amazonia, and the birth of the modern Amazon River system, Palaeogeogr., Palaeoclim atol ., Palaeoecol. 239 166 219 Campbell, K. E. ( 2010 ), Late Miocene onset of the Amazon River and the Amazon deep sea fan: Evidence from the Foz do Amazonas Basin: Comment, Geology 38 E212 E212. Carte r, L., R. M. Carter, I. N. McCave, and J. Gamble (1996), Regional sediment recycling in the abyssal southwest Pacific Ocean, Geology 24 735 738. Carter R. M., et al. ( 1999 ) Proceedings of the Oce an Drilling Program, Initial Reports vol. 181, Ocean Drill. Program, College Station, Tex. Carter L., and I. N. McCave ( 1997 ), Development of sediment drifts approaching an active plate margin under the SW Pacific Deep Western Boundary Current, Paleo ceanography 9 (6) 1061 1085. Carter L., and J. Wilkin ( 1999 ), Abyssal circulation around New Zealand A comparison between observations and a global circulation model, Marine Geology 159 221 239. Castro, J. C., K. Miura, and J. A. E. Braga ( 1978 ), St ratigraphic and structural framework of the Foz do Amazonas Basin, Annual Offshore Technology Conference Proceedings 3 1843 1847 Biostratigraphy at Site 999, Western Caribbean S ea, i n Proceedings of the Ocean Drilling Program Scientific Results ,165 edited by Leckie R. M. H. Siquardssom,, G. D. Acton, and G. Draper, pp. 19 56, Ocean Drilling Program, College Station, Texas. Coates A. G., J. B. Jackson, L. S. Collins, T. M. C ronin, H. J. Dowsett, L. M. Bybell, P. Jung, and J. A. Obando (1992) Closure of the Isthmus of Panama: the near shore marine record of Costa Rica and Western Panama Geol. Soc. Am. Bull. 104 814 828.

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122 BIOGRAPHICAL SKETCH Derrick Richard Newkirk was born in Indianapolis, Indiana He is the eldest son of Patricia and Richard Newkirk, and the older brother of Ryan Newkirk. His primary edu cation, elementary through high school, was complet ed in Greenwood, Indiana in the Center Grove School District While attending Indiana University Purdue University at Indianapolis he became interested in geology after taking an introductory course taught by Bob Barr. After completion of his four years of eligibility for collegiate soccer, he turned his focus to geology. During his undergraduate education he worked as a lab Dr. Jennifer Latimer. While working un der Dr. Gabriel Filippelli and Dr. Jennifer Latimer he worked on his own research project looking at human impacts on the watershed of Laguna Zoncho, Costa Rica using phosphorus geochemistry. This invaluable experience doing scientific research led him to graduate school. He completed his degree in the summer of 2004 with a Bachelor of Science with a focus in geology. At the University of Florida his research focused on the Miocene carbonate crash in the Caribbean using Nd isotopes in fossil fish teeth t o reconstruct ocean circulation. After completion of the Master of Science degree in July of 2007 he continued on at the University of Florida pursuing his Ph.D. under the guidance of Dr. Ellen Martin. While continuing his education at the University of F lorida, he tried to understand the global effects of the formation of Central America on the global pattern of ocean circulation. After graduation, he plans on pursuing a career in either academia or industry depending on job availability.