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Meltwater and abrupt climate change during the last deglaciation

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Title:
Meltwater and abrupt climate change during the last deglaciation a Gulf of Mexico perspective
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English
Creator:
Williams, Clare C
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University of South Florida
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Subjects / Keywords:
Paleoclimate
Younger Dryas
Oldest Dryas
Atlantic Warm Pool
Seasonality
Dissertations, Academic -- Marine Science -- Masters -- USF   ( lcsh )
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non-fiction   ( marcgt )

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Summary:
ABSTRACT: During the last deglaciation, Greenland ice core records exhibit multiple, high frequency climate events including the Oldest Dryas, Bølling-Allerød and Younger Dryas, which may be linked to meltwater routing of the Laurentide Ice Sheet (LIS). Previous studies show episodic meltwater input, via the Mississippi River to the Gulf of Mexico (GOM) several thousand years before the onset of the Younger Dryas until ~13.0 kcal (thousand calendar) yrs, when meltwater may have switched to an eastern spillway, reducing thermohaline circulation (THC). Data from laminated Orca Basin in the GOM, constrained by 34 Accelerator Mass Spectrometry (AMS) ¹⁴C dates, provide the necessary resolution to assess GOM sea-surface temperature (SST) history and test the meltwater routing hypothesis.Paired Mg/Ca and δ¹⁸O data on the Foraminifera species Globigerinoides ruber (pink and white varieties) document the timing of meltwater input and temperature change with decadal resolution. White G. ruber SST results show an early 5°C increase at 17.6-16.0 kcal yrs and several SST decreases, including at 16.0-14.7 kcal yrs during the Oldest Dryas (2°C) and at 12.9-11.7 kcal yrs during the Younger Dryas (2.5°C). While the early deglaciation shows strong similarities to records from Antarctica and Tobago Basin, the late deglaciation displays climate events that coincide with Greenland and Cariaco Basin records, suggesting that GOM SST is linked to both northern and southern hemisphere climate. Isolation of the ice-volume corrected δ¹⁸O composition of seawater (δ¹⁸Osubscript GOM) shows multiple episodes of meltwater at ~16.4-15.7 kcal yrs and ~15.2-13.1 kcal yrs with white G. ruber δ¹⁸Osubscript GOM values as low as -2.5%₀.The raw radiocarbon age of the cessation of meltwater in the GOM (11.375±0.40 ¹⁴C kcal yrs) is synchronous with large changes in tropical surface water Δ¹⁴C, a proxy for THC strength. An early meltwater episode beginning at 16.4 kcal yrs during the Oldest Dryas supports the suggestion of enhanced seasonality in the northern North Atlantic during Greenland stadials. We suggest a corollary to the seasonality hypothesis that in addition to extreme winters during stadials, warm summers allowed for LIS melting, which may have enhanced THC slowdown.
Thesis:
Thesis (M.S.)--University of South Florida, 2009.
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Includes bibliographical references.
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by Clare C. Williams.
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Title from PDF of title page.
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Document formatted into pages; contains 81 pages.

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usfldc doi - E14-SFE0002856
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Meltwater and Abrupt Climate Change During the Last Deglaciation: A Gulf of Mexico Perspective by Clare C. Williams A thesis submitted in the partial fulfillment of the requirements for the degree of Masters of Science College of Marine Science Univ ersity of South Florida Major Professor: Benjamin P. Flower, Ph.D. David W. Hastings, Ph.D. Albert C. Hine, Ph.D. Thomas P. Guilderson, Ph.D. Date of Approval: March 27, 2009 Keywords: paleoclimate, Younger Dryas, Oldest Dryas, Atlantic Warm Pool, seasonality Copyright 2009, Clare C. Williams

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i Table of Contents List of Tables ii List of Figures iii Abstract v Chapter One Deglacial Abrupt Climate Change in the Atlantic Warm Pool: A Gulf of Mexico Perspective 1 Introduction 1 Core Location and Methods 5 ICP MS Mg/Ca Method Development 7 Determination of Data Quality 9 Age Model 11 Orca Basin Sediments and Redox Conditions 13 SST Variability in the At lantic Warm Pool 16 Conclusions 20 Chapter Two Deglacial Laurentide Ice Sheet Meltwater and Seasonality Changes Based on Gulf of Mexico Sediments 22 Introduction 22 Core Location and Method s 26 Meltwater Routing Hypothesis 31 Changes in Seasonality During the Last Deglaciation 37 Conclusions 42 List of References 44 Appendix 1: Chapter One Figures 53 Appendix 2: Chapter Two Figures 68

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ii List of Tables 1 1. Acquired isotopes and respective dwell times for analysis on ICP MS. 8 A1 1. White G. ruber Mg/Ca, Al/Ca and Mn/Ca data from core MD02 2550. 54 A1 2. Radiocarbon age contro l for core MD02 2550. 63 A1 3. Magnetic susceptibility data for core MD02 550. 64 A2 1. Mg/Ca, Al/Ca and Mn/Ca pink G. ruber data from core MD02 2550. 69

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iii List of Figures 1 1. Comparison of NGRIP and EDML 18 O ice 4 1 2. Location map of the Gulf of Mexico and Caribbean Sea showing Orca Basin, Tobago Basin and Cariaco Basin. 6 1 3. Raw white G. ruber data vs. depth from core MD02 2550. 10 1 4. Age model for MD02 2550, based on 34 radioca rbon dates from monospecific planktonic Foraminifera ( G. ruber ). 12 1 5. Comparison of (a) Mn/Ca ratios and (b) magnetic susceptibility from core MD02 2550. 14 1 6. Comparison of SST records from the AWP and NGRIP. 17 2 1. Location map of Orca Basin and the Laurentide Ice Sheet (LIS). 27 2 2. Raw white and pink G. ruber data vs. depth from core MD02 2550. 29 2 3. Comparison of (a) NGRIP 18 O ice to 18 O GOM of (b) white and (c) pink varieties of G. ruber. 32 2 4. The Younger Dryas cessation event. 34 2 5. Comparison of (a) NGRIP 18 O ice to (b) "SST (calculated by subtracting white G. ruber SST from pink G. ruber SST), (c) whit e G. ruber Mg/Ca SST, and (d) pink G. ruber Mg/Ca SST. 40 A1 1. Comparison of culled white G ruber Mg/Ca and Al/Ca data. 61 A1 2. Comparison of culled white G. ruber Mg/Ca and Mn/Ca data. 61 A1 3. Comparison of all Mg/Ca and weight per Foraminifera data. A2 1. Raw pink G. ruber data vs depth from core MD02 2550. 80

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iv A2 2. Age model for core MD02 2550, based on 34 radiocarbon dates from monospecific planktonic Foraminifera ( G. ruber ). 81

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v Meltwater and Abrupt Climate Change During the Last Deglaciation: A Gulf of Mexico Perspective Clare C. Williams ABSTRACT During the last deglaciation, Greenland ice core records exhibit multiple, high frequency climate events including the Oldest Dryas, Blling Allerd and Younger Dryas, which may be linked to meltwater routing of the Laurentide Ice Sheet (LIS). Previous studies show episodic meltwater input, via the Mississippi River to the Gulf of Mexico (GOM) several thous and years before the onset of the Younger Dryas until ~13.0 kcal (thousand calendar) yrs, when meltwater may have switched to an eastern spillway, reducing thermohaline circulation (THC). Data from laminated Orca Basin in the GOM, constrained by 34 Accel erator Mass Spectrometry (AMS) 14 C dates, provide the necessary resolution to assess GOM sea surface temperature (SST) history and test the meltwater routing hypothesis. Paired Mg/Ca and 18 O data on the Foraminifera species Globigerinoides ruber (pink an d white varieties) document the timing of meltwater input and temperature change with decadal resolution. White G. ruber SST results show an early 5¡C increase at 17.6 16.0 kcal yrs and several SST decreases, including at 16.0 14.7 kcal yrs during the Old est Dryas (2¡C) and at 12.9 11.7 kcal yrs during the Younger Dryas (2.5¡C). While the early deglaciation shows strong similarities to records from Antarctica and Tobago Basin, the late deglaciation displays climate events that coincide with Greenland and Cariaco Basin records, suggesting that GOM SST is linked to both northern and southern hemisphere climate.

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vi Isolation of the ice volume corrected 18 O composition of seawater ( 18 O GOM ) shows multiple episodes of meltwater at ~16.4 15.7 kcal yrs and ~15.2 13.1 kcal yrs with white G. ruber 18 O GOM values as low as 2.5. The raw radiocarbon age of the cessation of meltwater in the GOM (11.3750.40 14 C kcal yrs) is synchronous with large changes in tropical surface water 14 C, a proxy for THC strength. An early meltwater episode beginning at 16.4 kcal yrs during the Oldest Dryas supports the suggestion of enhanced seasonality in the northern North Atlantic during Greenland stadials. We suggest a corollary to the seasonality hypothesis that in addition to extreme winters during stadials, warm summers allowed for LIS melting, which may have enhanced THC slowdown.

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1 Chapter One: Deglacial Abrupt Climate Change in the Atlantic Warm Pool: A Gulf of Mexico Perspective Introduction Evidence for abrupt climate change in Greenland ice core records indicates large temperature variations of 15 20¡C during the last degla ciation, based on calibrations to air temperature from 18 O Ice and borehole measurements. The Oldest Dryas, also known as Greenland Isotope Stadial 2a (Gs 2a) (~16.9 14.7 kcal yrs B.P.) [ Bjšrck et al. 1998; Rasmuss en et al. 2006] was a period of extreme cold, with 18 O Ice values becoming more negative than Last Glacial Maximum (LGM) conditions. The end of the Oldest Dryas and the subsequent abrupt onset of the Blling Allerd warm period (~14.7 12.7 kcal yrs B.P. ), also known as Greenland Isotope Interstadial 1 (GI 1), is seen as a 93¡C increase in Greenland air temperature at ~14,670 cal yrs B.P [ Cuffey and Clow 1997; Bjšrck et al. 1998; Severinghaus and Brook 1999; Ras mussen et al. 2006] Greenland ice core records also show two shorter abrupt cold events within the Blling Allerd period including the Older Dryas (~14.0 13.7 kcal yrs B.P.) and the Intra Allerd Cold Period (~13.35 13.00 kcal yrs B.P.) [ Rasmuss en et al. 2006] Lastly, the Younger Dryas was an extreme climatic reversal to near glacial conditions from ~12.9 11.7 kcal yrs B.P., with a duration of approximately 1,200 yrs [ Fairbanks 1990; Rasmussen et al. 2006] Paleo air temperature esti mations using the 18 O ice and borehole measurements show a 15¡C decrease compared to modern day, while snow accumulation rates were 3 times less during the Younger Dryas compared to modern accumulation rates (0.070.01 m ice/yr vs. 0.24 m ice/yr) [ Cuffey and Clow 1997] Methane gas concentrations decreased from approximately 700

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2 ppb to 475 ppb during the Younger Dryas, and increased to approximately 750 ppb at its termination [ Chappellaz et al. 1997; Severinghaus et al. 1998] As the natural source of methane is primarily wetlands and rainforests in tropical and subtropical regions, the decline in methane concentration in the Greenland ice cores during the Younger Dryas suggests that the climate of tropical regions was affected. Additionally, increases in [Cl ] and [Ca 2+ ] suggest changes in atmospheric circulation. High levels of chloride correspond to stronger and/or more frequent storms, while calcium, a primary comp onent of continental dust suggests windier conditions [ Mayewski et al. 1997] The Younger Dryas cold period is most strongly expressed in the North Atlantic region [ Broecker et al. 1988] North Atlantic SSTs (derived from Foraminiferal assemblages off the northern coast of Norway) exhibit a 6 8¡C decrease, suggesting increased dominance of Arctic Water [ Ruddiman 1977; Ebbesen and Hald 2004] Additionally, a sediment core off the Iberian margin at 37¡N, 10¡W, displays a 5¡C cooling using alkenone t emperature reconstructions and an increase of the number ice rafted debris (IRD)/gram sediment from zero to approximately 80 [ Bard et al. 2000] North Atlantic circulation, specifically the Gulf Stream, which turns into the North Atlantic Current, was a ffected during the Younger Dryas. The modern North Atlantic is warmed by tropical waters in the Gulf Stream that hug the North American coastline from Florida to North Carolina, and then diverge east towards Europe as the North Atlantic Current. These wa ters are a primary source of heat to the European region. Arctic Water from the polar front moved further south almost to its glacial position at 45¡N, also forcing the warm North Atlantic Current south of northern Europe. Northern European lake sediment s display a shift in pollen assemblages indicating a reduction in pine birch forests and an expansion of open habitats [ Goslar et al. 1993; Bjšrck et al. 1996; Brauer et al. 1999; Demske et al. 2005] Sediments from Lake MadtjŠrn, Sweden, display a reduction of tree pollen such as Betula alba (birch) and Pinus pollen and an

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3 increase in shrubs and herbs including Dryas octopetala, Juniperus and Artemisia [ Bjšrck et al. 1996] Greenland and Antarctic ice core records, correlated by methane gas concentrations are not in phase during the deglacial period [ Broecker and Denton 1989; Broecker 1998; Stocker 2000; Blunier and Brook 2001; Morgan et al. 2002; EPICA 2006] (Figure 1 1). While Antarctic records display a warming trend initiated at ~19.0 kcal yrs B.P. and increasing until ~14.0 kcal, Greenland ice cores exhibit only a slight warming at ~19.0 kcal followed by intense cooling during the Oldest Dryas unt il the onset of the Blling Allerd at ~14.7 kcal. From ~14.0 12.0 kcal, Antarctic records display an abrupt cool period known as the Antarctic Cold Reversal (ACR), roughly coinciding with the Blling Allerd warm period. Antarctic temperatures begin to increase during the Younger Dryas period at around 12.5 kcal before stabilizing at the Younger Dryas termination at ~11.7 kcal. This anti phase behavior has been termed the bipolar seesaw [ Broecker 1998; Stocker 2000]

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4 -46 -44 -42 -40 -38 -36 -34 NGRIP 18 O ice ( VSMOW) a -51 -49 -47 -45 -43 10 12 14 16 18 20 EDML 18 O ice ( VSMOW) GICC05-Scale CH 4 Gas Age (kcal yrs B.P.) b YD OD Figure 1 1 Comparison of NGRIP and EDML 18 O ice Greenland and Antarctica 18 O ice records are not in phase. Antarctica exhibits warming trends during abrupt cold events in Greenland including the Oldest Dryas (OD) and Younger Dryas (YD) (shaded). Source: [ EPICA 2006] Proxy SST records from the Atlantic Warm Pool (AWP), encompassing the Gulf of Mexico (GOM) and Caribbean Sea, exhibit inconsistent responses to abrupt climate change during the deglacial period [ RŸhlemann et al. 1999; Lea et al. 2003] Alkenone derived SST from a sediment core in Tobago Basin, in the western tropical Atlantic, exhibits an in phase relationship with Antarcti ca temperatures during the last deglaciation, displaying a 1.5¡C SST increase at ~19.0 15.5 kcal yrs B.P. through the Oldest Dryas. Temperatures cool slightly during the Blling Allerd and increase ~1.0¡C during the Younger Dryas [ RŸhlemann et al. 1999] In contrast with the results from Tobago Basin,

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5 Cariaco Basin, located off the north central Venezuelan coast, exhibits synchronous changes in SST to Greenland ice core record s, including ~1.5¡C and ~4.0¡C SST decreases at ~ 16.4 14.7 kcal and 12.8 11.4 kcal yrs B.P. (Oldest and Younger Dryas), respectively. In addition to abrupt cold events, Cariaco also exhibits a well defined Blling Allerd warm period [ Lea et al. 2003] In order to help resolve deglacial SST patterns in the AWP, we present a new, high resolution Mg/Ca SST record from the GOM from 18.8 10.6 kcal yrs B.P. Our new SST record suggests a strong linkage to Antarctic clim ate during the early deglacial period (18.5 16.0 kcal yrs B.P.) and to Greenland during abrupt climate events. A large SST increase at ~14.7 kcal yrs B.P. followed by distinct cooling from ~12.9 11.7 kcal yrs B.P. confirms the presence of the Blling Alle rd and Younger Dryas in the GOM. Core Location and Methods Located in the northern GOM, approximately 300 km from the current Mississippi River delta, Orca Basin currently has an anoxic brine pool (salinity >250) that provides a laminated, non bioturbate d record of GOM paleoceanography (Figure 1 2). High sedimentation rates (~40 cm/1000 yrs) allow for high resolution sampling at nearly decadal resolution and abundant aragonite pteropod tests suggest negligible carbonate dissolution throughout the core.

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6 Figure 1 2. Location map of the Gulf of Mexico and Caribbean Sea showing Orca Basin, Tobago Basin and Cariaco Basin. Source: Online Map Creation (http://aquarius.geomar.de/) Core MD02 2550 (9.09 m giant 25 cm 2 Calypso gravity core), recovered from 224 8 m water depth (26¡56.78' N, 91¡20.75' W) by the R/V Marion Dufresne in 2002, was sampled every half cm from core top to 466 cm, and every 1 cm to 908cm. All samples were freeze dried, wet sieved and washed over a 63 m mesh with deionized water. When available, approximately 30 40 individuals of the planktonic Foraminifera species Globigerinoides ruber (white variety) were picked from the 250 355 m size fraction for elemental ratio analysis. Once picked, sample s were sonicated with methanol for 5 seconds to remove fossil particles from inside the G. ruber tests, dried and weighed. Samples were lightly crushed between 2 glass plates and extensively cleaned for Mg/Ca analyses [ Barker et al. 2003] The Cambridge cleaning process includes multiple trace metal clean wat er and methanol rinses to remove clays, an oxidizing treatment with a buffered peroxide solution to remove organic material

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7 and a weak acid leach to remove adsorbed particles. Samples were then dissolved in a weak 0.001 N HNO 3 solution, diluted to a targe t calcium concentration of ~ 25 ppm and analyzed on an Agilent Technologies 7500 cx inductively coupled plasma mass spectrometer (ICP MS). SST was calculated using the Anand et al. (2003) calibration curve for white G. ruber (Mg/Ca= 0.449 0.09*SST ). Instr umental precision for Mg/Ca is 0.01 mmol/mol, based on analyses of approximately 1500 reference standards, over the course of 16 runs. Average standard deviation of 37 replicate Mg/Ca analyses (17%) is 0.076 mmol/mol. ICP MS Mg/Ca Method Development T he Agilent Technologies 7500cx ICP MS, installed at the College of Marine Science at the University of South Florida in 2008, uses a ASX 500 autosampler, MicroMist concentric nebulizer and double pass (Scott type) quartz spray chamber, Peltier cooled to 2¡ C. Mg/Ca method development for the ICP MS included determination of acquired isotopes, integration times, number of repetitions, peristaltic pump set up, and optimal tuning parameters. A fully quantitative isotope analysis acquisition mode was used, for which 3 central peak points were measured for each mass. Acquired isotopes and respective integration times are shown in Table 1 1. Five repetitions per sample were acquired to ensure reproducibility. Due to inherently small sample volume, the peristalt ic pump was optimized to handle volumes ranging from ~3.0 ml to 0.5 ml. A 55 second rinse time was used to reduce any sample to standard contamination. Prior to each run, the ICP MS was tuned for low (<2%) oxides and doubly charged molecular interference s as well as low relative standard deviations (RSDs). A 100 ppb Ca solution was run for 30 minutes prior to each run for cone conditioning.

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8 Table 1 1. Acquired isotopes and respective dwell times for analysis on the ICP MS. Analyte Detection Mode In tegration time per point a (sec) Mean Blank cps (counts per second) 26 Mg Analog 0.1 20,556 27 Al Analog 0.4 22,028 43 Ca Analog 0.1 36,638 55 Mn Analog 0.1 24,653 a Each of the 5 replicates includes 1000 scans through all acquired masses. Dwell time = I ntegration time/1000. Multiple standards were used to ensure optimal accuracy and precision. As high calcium (Ca) concentrations may cause machine drift and affect Mg/Ca ratios, a series of experimental runs was performed to establish the potential calci um concentration effect on Mg/Ca ratios and determine an ideal Ca concentration for sample dilution. Ten dilutions of four individual solutions with varying Mg/Ca values, ranging from 2.1 8.2 mmol/mol were analyzed to determine an ideal Ca concentration r ange for which there was no change in Mg/Ca. Similar runs were replicated to ensure consistency. Although experimental run results showed insignificant differences between varying Ca concentrations and Mg/Ca ratios, five serial dilutions of three Mg/Ca r atio standards were analyzed before and after all sample analyses during each run. In addition to serial dilutions used to monitor the calcium concentration effect, a powdered CaCO 3 standard (ECRM 751) was analyzed 6 times per run to allow for inter labor atory comparison, in accordance with [ Greaves et al. 2008] Following [ Schrag et al. 2002] a reference solution with a known Mg/Ca ratio, was alternated with serial dilutions, ECRM 751 and samples to further calibrate and correct for instr umental drift. Five calibration standards for Mg and Ca and five for Mn and Al were analyzed in the beginning of each run to calibrate samples from count per second measurements to concentration.

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9 Determination of Data Quality To assess data quality of t he Mg/Ca data set, Al/Ca, Mn/Ca and weight per Foraminifera measurements were used to monitor clay removal, Mn Fe oxides and the preferential removal of Mg due to the effects of dissolution, respectively (Figure 1 3). Cleaning procedures and clay removal were monitored by Al/Ca ratios [ Barker et al. 2003; Lea et al. 2005; Pena et al. 2005] Data with Al/Ca ratios greater than 200 mol/mol were eliminated (approx 8% of samples) from the plots as their Mg/Ca values might be influenced by excess Mg from insufficient clay removal. For completeness all results are reported in Table A1 1. T here is no correlation between Al/Ca and Mg/Ca ratios for whole (r 2 = 0.02) or culled data (r 2 = 0.05) (Figure A1 1). Although no Mn/Ca threshold was used to eliminate samples, there is also no correlation between Mn/Ca and Mg/Ca ratios (r 2 = 0.02) (Figure A 1 2). Weight per Foraminifera values are relatively constant down core.

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10 -50 0 50 100 150 200 G. ruber Al/Ca ( mol/mol) 0 1 2 3 4 5 6 300 350 400 450 500 550 600 650 % Abundance of G. inflata Depth (cm) 2 2.5 3 3.5 4 4.5 5 5.5 G. ruber Mg/Ca (mmol/mol) a b c Figure 1 3. Raw white G. ruber data vs. depth from core MD02 2550. (a) Mg/Ca data. Average precision is 0.01 mmol/mol. (b) Al/Ca data are used to monitor clay removal. No cor relation is seen between Al/Ca and Mg/Ca values (r 2 = 0.05). (c) % Abundance of G. inflata a cold water planktonic Foraminifera. ICP MS instrumental precision is 0.01 mmol/mol.

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11 Age Model Thirty four accelerator mass spectrometry (AMS) 14 C dates, betwee n 308 and 614 cm, from monospecific G. ruber (white and pink varieties) provide the chronological control (Table A1 2). Raw radiocarbon ages were calibrated to calendar years using Calib 5.0.2, which applies the most recent radiocarbon to calendar age cal ibration (MARINE04), and uses an assumed constant reservoir age correction of 405 yrs [ Stuiver et al. 1998; Hughen et al. 2004; Reimer et al. 2004] The third order polynomial used in the calibration fits 30 out of 34 calibrated dates for the age model (Figure 1 4). Error bars represent 2 sigma error in calibration from radiocarbon to calendar years. Error increases dramatically at ~14.6 kcal due to the increased calibration uncertainty. The MARINE04 data set includes 14 C dated Foraminifera from annually varved sediments from Cariaco Basin from 10.5 14.7 kcal B.P., but only coral records constrain the calibration line for samples older than 14.7 kcal [ Hughen et al. 2004] Mean accumulation is 40 cm/1000 yrs. Half cm sample resolution between 310 cm and 466 cm yields a mean temporal resolut ion of 13 yrs/ sample, while 1 cm sample resolution from 466 621 cm is 24 yrs/ sample.

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12 10,000 12,000 14,000 16,000 18,000 20,000 300 350 400 450 500 550 600 650 Calendar Yrs B.P. Depth (cm) Y=(3.205 x 10 4 )x 3 0.4545x 2 + 232.5x (2.738 x 10 4 ) Figure 1 4. Age model for core MD02 2550, based on 34 radiocarbon dates, from monospecific planktonic Foraminifera ( G. ruber ). Error bars represent 2 sigma error i n calibration from radiocarbon to calendar years. All 14 C dates were calibrated to calendar years using the MARINE04 calibration data set [ Hughen et al. 2004] and have an assumed constant 405 yrs reservoir correction applied. Because of the uncertainty associated with calendar year calibration, a more direct approach is necessary to e xamine the relative timing of deglacial events in the AWP. Recent evidence suggests that reservoir ages have changed significantly during the deglaciation, which may affect calibration to calendar years [ Goslar et al. 1995; Waelbroeck et al. 2001] Reservoir age calculations based on corals from the GOM and Cariaco Basin suggest that due to surface water current patterns, both locations currently have the same reservoir age

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13 [ Wagner et al. In press] With the assumption that AWP reservoir changes were synchronous (within error) during the deglaciation, we can directly compare GOM and Cariaco Basin raw radiocarbon ages, and then to Greenland ice core records to avoid unnecessary calibration error. Orca Basin Sediments and Redox Conditions Orca Basin is a unique environmental and depositional setting, where good preservation of organic and inorganic matter is attributed to a large, 220m deep brine lake within the basin [ Sackett et al. 1977; Shokes et al. 1977; Pilcher and Blumstein 2007] The brine lake itself, with an area of ~123 km 2 was formed from the deformation and subsequent exposure and dissolution of the Jurassic Louann Evaporite Formation [ Pilcher an d Blumstein 2007] The degradation of organic matter in marine sediments follows a specific pathway of redox reactions, based on the availability of oxygen and other electron acceptors [ Froelich et al. 1979] In oxic sedimentary environments, dissolved oxygen is the preferre d electron acceptor for the degradation of organic matter. When dissolved oxygen becomes depleted, biologically mediated reactions require another electron acceptor for the oxidation of organic matter: manganese oxides. The oxidation of organic matter us ing particulate manganese (IV) oxides yields almost as much free energy as the oxygen (3090 vs. 3190 kJ/mol) and produces dissolved reduced manganese, typically as dissolved Mn(II) in sedimentary pore water. The dissolved Mn(II) diffuses out of the sedime nt to overlying oxygenated waters, where Mn(II) is re oxidized and precipitated as manganese (IV) oxide. Iron (III) oxides and iron (III) hydroxides may also serve as electron acceptors in low oxygen conditions. Iron (III) oxide reduction yields ~1410 JK/ mol energy during the degradation of organic matter. In oxic regions where it is not necessary to oxidize matter with iron oxides, magnetite and other iron oxides, which yield high magnetic susceptibility values, dominate the sediments. When oxygen level s decrease and other electron acceptors are required for

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14 organic matter degradation, magnetite (Fe 3 O 4 ) is reduced to Fe(II), which subsequently yields low magnetic susceptibility values. In summary, intervals where magnetic susceptibility is high, the sed iments should be dominated by iron oxides, which are stable in oxic conditions, and low values are more commonly found in anoxic conditions. Core MD02 2550 exhibits multiple intervals of faintly laminated to strongly laminated sediments (Figure 1 5). From approximately 18.5 17.2 kcal yrs B.P., no laminations are present. At ~17.2 kcal, faint laminations appear and from 15.9 12.5 kcal, strong laminations are present, followed by very faint laminations until ~10.6 kcal. These laminations are inferred to be due to the lack of bioturbation, likely during anoxic intervals. 0 200 400 600 800 1,000 1,200 1,400 Mn/Ca ( mol/mol) of G. ruber Strongly Laminated Faintly Laminated No Laminations Very Faintly Laminated 5 10 15 20 25 30 10 12 14 16 18 20 Magnetic Susceptibity ( ) Calendar Age (kcal yrs B.P.) a b Figure 1 5. Comparison of (a) Mn/Ca ratios and (b) magnetic susceptibility from core MD02 2550. Both records show decreased values from ~16.4 13.2 kcal yrs B.P.

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15 Magnetic susceptibility a nd elemental analyses from core MD02 2550 may provide new insights on the controls of sediment laminations, oxic/anoxic conditions and redox reactions in Orca Basin during the deglacial period. Low field magnetic susceptibility was measured using a small diameter Bartington coil on board the Marion Dufrense in 2002. Magnetic susceptibility measurements decrease to ~5 (10 6 SI) from ~16.4 13.2 kcal yrs B.P (Figure 5, Table S3), suggesting low oxygen conditions. During the same interval, Mn/Ca of G. ruber Foraminiferal tests also exhibits low values (~200 mol/mol) suggesting that no Mn Fe oxide coatings are present on G. ruber tests. Although these coatings are thought to be high in Mg, which may affect SST calculations, the lack of correlation (r 2 = 0.02) between Mn/Ca and Mg/Ca indicates that these coatings may be relatively low in Mg (Figure S2). The large difference in Mn/Ca values at ~16.4 13.2 kcal yrs B.P. suggests that G. ruber in Orca Basin are recording post depositional geochemical sedimentary conditions. Specifically, G. ruber Mn/Ca ratios support mag netic susceptibility measurements that suggest anoxic conditions in Orca Basin from ~16.4 13.2 kcal yrs B.P. Anoxic conditions in Orca Basin may be caused by an increase in nutrient and organic material input to region due to Laurentide Ice Sheet (LIS) mel twater. Meltwater brings increased nutrient and terrestrial organic matter from the North American continent. Elevated nutrient concentrations allow for enhanced productivity followed by increases in organic matter, which deplete bottom water oxygen leve ls during respiration. The basin becomes anoxic, no organisms can survive, which decreases bioturbation, and allows laminations to form. Previous research from Orca Basin suggests that meltwater is present from at least 16.0 12.9 kcal yrs B.P. [ Flower et al. 2004]

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16 SST Variability in the Atlantic Warm Pool White G. ruber is an excellent paleo SST recorder as it inhabits the upper 50 m of the tropical to subtropical water column [ BŽ and Hamlin 1967] Although currently there is no seasonal distribution record for Foraminifera in the GOM, Sargasso Sea sediment trap data suggests that white G. ruber species live throughout the year [ Deuser et al. 1981; Deuser 1987; Deuser and Ross 1989] During the deglaciation, G. ruber Mg/Ca derived SST exhibits an early deg laciation (mean = 19.0¡C) to early Holocene (mean = 24.6¡C) range of ~5.6 ¡C (Figure 1 6). A step wise SST increase (~ 5¡C) is seen during the early deglacial period from approximately 17.6 16.0 kcal, followed by a ~2¡C cooling from 16.0 14.7 kcal. A shar p increase in SST (~3.5¡C) begins at ~14.7 kcal, peaking at 14.0 ka. From 14.7 12.9 kcal, warm SSTs dominate with multiple short cool periods superimposed (~ 1.5¡C SST decrease; <200 yrs). From 12.9 11.7 ka, SSTs decrease by approximately 2.5¡C, followe d by an increase to approximately 24.5¡C at 10.6 kcal. Faunal assemblage data, specifically % abundance of the cold water species Globorotalia inflata supports distinct cooling initiating at approximately 13.4 12.9 kcal yrs B.P. (Figure 1 3).

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17 -46 -44 -42 -40 -38 -36 -34 18 O ice (VSMOW) North GRIP (75¡N, -42¡W) 10 12 14 16 18 20 24 25 26 27 28 Alkenone-SST (¡C) Age (kcal yrs B.P.) Tobago Basin (12¡N, 61¡W) M35003-4 18 20 22 24 26 28 Mg/Ca-SST (¡C) Gulf of Mexico (26¡N, 91¡W) MD02-2550 22 23 24 25 26 27 28 29 Mg/Ca-SST (¡C) Cariaco Basin (10¡N, 64¡W) PL07-39PC Figure 1 6. Comparison of SST records from the AWP and NGRIP. The Mg/Ca SST records from the Gulf of Mexico and Tobago Basin are dominated by an Antarctic signal from 18.5 16.0 kcal. From 16.0 to 10.6 kcal, GOM SST exhibits similar climate features to Cariaco an d Greenland, including Oldest and Younger Dryas cold periods. Average precision based on replicate analysis for white G. ruber Mg/Ca SST is 0.3 ¡C Sources: [ RŸhlemann et al. 1999; Lea et al. 2003; Rasmussen et al. 2006]

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18 Our new Mg/Ca SST record allows us to re evaluate the discrepancy in the AWP climate history recorded in Cariaco Basin and Tobago Basin records. Greenland ice cores and European lake sediments record 3 major abrupt climate events are resolv ed in the GOM SST record that may be correlative with the Oldest Dryas (16.0 14.7 kcal yrs B.P.), Blling Allerd (14.7 12.9 kcal), and the Younger Dryas (12.9 11.7 kcal) (Figure 1 6). The early deglacial (18.5 16.0 kcal yrs B.P.) GOM SST record exhibits strong similarities to Tobago Basin with an r 2 = 0.95. Although Tobago Basin SST changes are more subtle than GOM SST, both records show a temperature increase from ~17.6 16.0 kcal yrs B.P. (Figure 1 6). Mg/Ca SST records from Cariaco Basin and the GOM ex hibit similarities during high frequency abrupt climate events during the late deglaciation (16.0 10.5 kcal yrs B.P.) including Oldest Dryas, Blling Allerd and Younger Dryas. While Cariaco Basin displays a ~1.5¡C SST reduction at ~ 16.4 14.7 kcal yrs B. P. [ Lea et al. 2003] during the Oldest Dryas, the GOM exhibits a ~2.0¡C cooling at ~16.0 14.7 kcal. Both Cariaco Basin and the GOM exhibit a SST increase at the onset of the Blling Allerd warm period (3.0¡C and 3.5¡C, respectively) at ~14.7 kcal yrs B.P. Although both records also show superimposed millennial scale cool periods, the radiocarbon measurement error and subsequent chronology issues prevent such short intervals to be precisely correlated. The Younger Dryas event, also present in both Cariaco Basin and the GOM, is manifested as a SST decrease (4.0¡C and 2.5¡C, respectively) at ~12.9 kcal yrs B.P. While the onset of the Younger Dryas is very abrupt (transition <300 yrs) in Cariaco Basin, the low number s of G. ruber individuals and consequent low sample resolution prevents us from determining the rapidity of initial GOM cooling. Tobago Basin exhibits a small but significant warming of 0.8¡C during the Younger Dryas interval. In summary, the Mg/Ca SST G OM record has similarities to both Cariaco Basin and Tobago Basin during the deglaciation. Most notably, the GOM exhibits rapid SST increase during the

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19 early deglacial (18.5 16.0 kcal yrs B.P.) like Tobago Basin, and high frequency abrupt climate events i n the late deglacial period (16.0 10.5 kcal) like Cariaco Basin. Although the GOM SST record provides an important link in determining the SST history of the AWP, more Caribbean climate records are needed to fully establish regional patterns. The northern GOM, while still a part of the AWP, may be affected by different processes than Cariaco and Tobago Basins due to its close proximity to the North American continent. The massive LIS and associated lowered sea level would have further decreased Orca Basin 's distance from the Mississippi River and may have allowed it to become susceptible to regional continental cooling. In addition to AWP records, the GOM SST record can be compared to high latitude ice cores to determine the relative importance of northern and/or southern hemisphere relationships with the low latitude regions. The early deglacial (18.5 16.0 kcal yrs B.P.) GOM SST record exhibits strong similarities to Antarctic 18 O ice with an r 2 = 0.72. The 5¡C SST increase in the GOM from 18.5 16.0 kca l yrs B.P., is close in timing to the 18 O ice increase in the EPICA record [ Jouzel et al. 2001] G. ruber SST displays a significant correlation with NGRIP 18 O ice from 18.4 10.6 kcal yrs B.P. (Figure 1 6). In NGRIP, the Oldest Dryas stadial (16.9 14.7 kcal yrs B.P.) is a period of extreme cold with 18 O ice values as negative as 44 centered at 16.0 kcal [ Rasmussen et al. 2006] GOM G. ruber records a similar cold event from 15.8 to 14.5ka with an SST decrease of 2¡C. GOM cooling does not span the entire Oldest Dryas period. GOM G. ruber also exhibits a 3.5¡C SST increase at ~14.7 kcal yrs B.P. that coincides with the onset of the Bll ing Allerd warm period. As with NGRIP record, the GOM displays a SST peak at ~ 13.8 kcal (~25.5¡C) followed by a slow cooling trend with short abrupt cold events superimposed. Although the Younger Dryas event is prevalent in most northern hemisphere hig h latitude records, this study is the first to document its existence in the GOM using Mg/Ca

PAGE 27

20 SST, which illustrates the strong relationship between the Atlantic low latitudes and northern hemisphere climate. Overall, our GOM SST record suggests that the AW P is linked to both southern and northern hemisphere climate change. During the late deglacial period (16.0 10.5 kcal yrs B.P.), when GOM SST correlates with Cariaco Basin and NGRIP abrupt climate events, a strong linkage between northern hemisphere clima te change suggests that at least 2 records from the AWP are partially controlled by northern hemisphere climate. Although a decrease in NADW should warm low latitude regions, because the proximity of core MD02 2550 to the North American continent, GOM SST may be responding to regional cooling due to the presence of the LIS. Strong similarities between Tobago Basin, EPICA 18 O ice and GOM SST during the early deglacial period (18.5 16.0 kcal yrs B.P.) supports the suggestion that the AWP is linked to souther n hemisphere warming. Additionally it is possible that the similarities are due to GOM SST record exhibits similarities toward Greenland due to NADW reduction. AWP warming may be due to heat buildup in the tropics and subtropics due to a decrease in NADW formation and a subsequent reduction in poleward heat transport [ Crowley 1992] W hen NADW formation is in a reduced state, modeling experiments show a decrease in poleward heat transport, producing tropical and subtropical warming due to excess heat build up near the equator and in the southern hemisphere [ Crowley 1992; Manabe and Stouffer 1997; RŸhlemann et al. 1999] Thus, NADW reduction, during cold periods in the northern high latitudes, may cause warming in the low latitude Atlantic Ocean. Other studies suggest that this early warming m ay be a globally dominated signal [ Schaefer et al. 2006] Conclusions The GOM Mg/Ca SST record exhibits a 5.6¡C early deglacial to early Holocene SST range with distinct (~2¡C) cooling during the inferred Oldest Dryas and Y ounger Dryas intervals. The Blling Allerd warm period displays a 3.5¡C

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21 SST increase. These results are first to capture the Younger Dryas in the GOM based on Mg/Ca SST and broaden the extent of North Atlantic cooling. Comparison to Greenland and Antarc tic records suggests that the AWP is significantly affected by both northern and southern hemisphere climate. As the GOM exhibits similarities to Antarctica in the early deglacial period, this may be due to a global temperature increase or changes in ther mohaline circulation which created a buildup of heat in the AWP and southern hemisphere. Abrupt climate events seen in Greenland records are also recorded in GOM climate and suggest that rapid climate changes that affect the North Atlantic region also inf luence the AWP. Magnetic susceptibility and elemental analyses also provide insight on the controls of sediment laminations and oxygen conditions in Orca Basin. Both magnetic susceptibility and Mn/Ca ratios of G. ruber suggest very low oxygen conditions w ithin Orca Basin at ~16.4 13.2 kcal yrs B.P. The presence of laminations from ~16.0 12.5 kcal suggests a linkage between low oxygen levels and laminated sediments, possibly controlled by bioturbation. Additionally, as laminations and anoxia occur during periods of meltwater input, both may be driven by an increase in terrestrial organic input to the basin and enhanced primary productivity.

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22 Chapter Two: Deglacial Laurentide Ice Sheet meltwater and seasonality changes based on Gulf of Mexi co sediments Introduction Ice sheet melting dynamics and the formation and drainage of proglacial lakes may have played a significant role in abrupt climate change, including reductions/shutdowns of North Atlantic Deep Water (NADW) due to meltwater releas e into the North Atlantic and Arctic oceans via routes including the Mackenzie River, St. Lawrence River, Hudson River, and Hudson Strait during the last deglaciation [ Rooth 1982; Boyle and Keigwin 1987; Broecker e t al. 1989; Clark et al. 2001; Tarasov and Peltier 2005; Broecker 2006b] As warm Gulf Stream waters travel north, high evaporation, low precipitation and low continental runoff produce saline waters that cool in the boreal winter and sink to great de pths in areas of NADW formation, such as the Greenland and Norwegian Seas. During the last deglaciation, glacial meltwater may have entered the North Atlantic, forming a freshwater cap over regions of NADW formation, which subsequently reduced deepwater p roduction and the global ocean "conveyor belt" [ Broecker 1991] Reduced advection of warm Gulf Stream surface waters and formation of se a ice would result in a period of cooler temperatures in the North Atlantic region. Meltwater routing changes may be dependent on small latitudinal changes in ice sheet margin location, specifically between 43¡ and 49¡ N. When melting along the southern L aurentide Ice Sheet (LIS) margin occurs, meltwater, either from glacial lakes such as Lake Agassiz or directly from the LIS may be re routed from the southern outlet to an ice free eastern spillway into the North Atlantic. The influx of freshwater into th e North Atlantic may then cause a reduction in

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23 thermohaline circulation (THC) leading to widespread cooling of the North Atlantic region and subsequently an advance of the southern ice sheet margin. With the eastern spillway covered with newly re advanced ice, meltwater would then be re routed to a southern spillway, allowing THC to increase. Oscillations between a more northern vs. southern ice sheet margin and the associated meltwater re routing may be an important mechanism controlling changes in NADW, North Atlantic sea surface temperature (SST) and abrupt climate change [ Clark et al. 2001] Early in the last deglaciation, the Mississippi River served as an important conduit for meltwater to the Gulf of Mexico (GOM) [ Kennett and Shackleton 1975; Broecker et al. 1989; Flower and Kennett 1990; Clark et al. 2001; Aharon 2003; Fisher 2003; Flower et al. 2004] Negative 18 O sw excursions greater than 1, suggesting meltwater presence in the GOM, are found from approximately 16.1 15.6 kcal yrs B .P. and 15.2 13.0 kcal yrs [ Flower et al. 2004] Most studies find no eviden ce of meltwater input into the GOM directly after the onset of Younger Dryas (12.9 11.7 kcal yrs B.P.) and it is thought that meltwater routing switched to another spillway at this time [ Broecker et al. 1989; Flower and Kennett 1990; Clark et al. 1993; Clark et al. 2001; Fisher 2003; Flower et al. 2004; Tarasov and Peltier 2005; Broecker 2006b] The timing of meltwater reduction to the GOM is not well constrained. If meltwater routing caused the Younger Dry as, evidence for a decrease in meltwater to the south should coincide with an increase in meltwater flux to the North Atlantic as well as a reduction in THC. Most geochemical studies show no definitive evidence for the presence of meltwater in the North At lantic during the Younger Dryas. Keigwin and Jones (1995) found a distinct increase in the abundance of N. pachyderma a coldwater dwelling Foraminifera species, during the Younger Dryas but no isotopic signal of meltwater in Gulf of St. Lawrence. de Ver nal and Claude (1996) also found no evidence of a meltwater signal in dinoflagellates nor in the 18 O of Foraminifera in the mouth of the St. Lawrence River.

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24 One recent study based on Mg/Ca, U/Ca and 87 Sr/ 86 Sr of planktonic Foraminifera is interpreted to i ndicate the presence of meltwater in the mouth of the St. Lawrence River [ Carlson et al. 2007] The interp retation of an excess Mg/Ca signal due to continental runoff from the Canadian Shield relies on a complicated combination of geochemical and assemblage based proxy data, with large error propagation. Therefore, the approach used may not be appropriate for accurately determining a meltwater signal. The lack of geomorphological evidence for eastern routing of meltwater from the LIS and Glacial Lake Agassiz at the onset of the Younger Dryas further questions the possibility of eastern meltwater flow to the No rth Atlantic. Aerial surveys of the Thunder Bay area, situated on the northwestern shores of Lake Superior, a postulated conduit to the St. Lawrence River and/or Hudson River, show no distinct geomorphic evidence of flooding [ Lowell et al. 2005; Teller et al. 2005] Radiocarbon ages and varve counts of laminated clays in the Shebandowan lowland in Thunder Bay reveal that the region was either still glaciated or completely subme rged in glacial lake water until at least 10.2 14 C kcal yrs B.P. [ Lowell et al. 2005; Teller et al. 2005; Broecker 2006b] An alternative explanation for the lack of geomorphological evidence is that the radiocar bon age of glaciation is not from the initial onset but during and after the Younger Dryas and after the glacial re advance [ Lowell et al. 2005] Teller et al. (2005) believe that there was no catastrophic outflow, but a moderate flow over a longer period of time, for which no evidence for meltwater floods would exist. There is ample evidence of northwest routing of Lake Agassiz meltwater to the Arctic Ocean via the Clearwater and Athabasca Rivers to the Mackenzie Valley [ Fisher et al. 2002; Lowell et al. 2005; Broecker 2006b] Aerial surveys of the Fort McMurray, Alberta region (encompassing both the Clearwater and Athabasca Rivers) show significant geomorphic features consistent with a meltwater flood. However, wood fragments from flood deposits were dated at 9.860 0.23 14 C kcal yrs B.P., approximately 1000 14 C yrs after the Younger

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25 Dryas began [ Fisher et al. 2002] Stony Mountain, Firebag, and Cree Lake Moraines in the Fort McMurray region w ere dated 10.030, 9.595 and 9.665 14 C kcal yrs B.P., indicating meltwater may have flowed through the Clearwater channel after approximately 10.0 14 C kcal yrs B.P. [ Lowell et al. 2005] In summary, based on terrestrial evidence, meltwater routing t o the North Atlantic appears to have occurred well after the onset of the Younger Dryas approximately 11.0 14 C kcal yrs B.P. Alternatively, more recent episodes of flooding may have wiped out all evidence of previous floods [ Broecker 2006b] Other possible meltwater sources include sub ice flow [ Barber et al. 1999; Broecker 2006b] the melting of an armada of icebergs and/or a massive Arctic marine ice sheet [ Bradley and England 2008] In either scenario, continental geomorphic changes would not be recorded [ Broecker 2006b] Recent research suggests that cold periods such as the Younger and Oldest Dryas were intervals of increased seasonality, possib ly driven by meltwater release into the North Atlantic [ Denton et al. 2005 ; Broecker 2006a] While isotopic measurements on N 2 and Ar 2 in air bubbles trapped Greenland ice cores exhibit a 16¡C decrease in air temperature [ S everinghaus et al. 1998] during the Younger Dryas, reconstructions based on lateral moraine elevations only show a 4 6¡C cooling [ Funder 1989] As isotopic measurements have been determined to represent mean annual temperature and lateral moraine elevations estimate primari ly summer conditions, winters during the Younger Dryas must have been an average of 26 28¡C colder than modern [ Denton et al. 2005] The salinity reduction associated with meltwater input, combined with the lack of heat transport would have allowed extensive sea ice to form and cover the entire Norwegian Sea, creating extremely cold winter conditions. Modeling experiments show that if sea ice coverage increased in the North Atlantic, the Inter Tropical Convergenc e Zone (ITCZ) would be shifted southward [ Chiang et al. 2003] and monsoons would be weakened [ Barnett et al. 1988] as suggested by existing tropical and subtropical data.

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26 To investigate the timing of meltwater input throughout the last deglaciation, we studied the 18.5 10.6 kcal yrs B.P. interval in a sediment core from laminated Orca Basin in the GOM. Paired Mg/Ca and 18 O Calcite (! 18 O C ) analyses on 2 varieties of planktonic Foraminifera resolve millennial scale SST changes and high frequency meltwater episodes. We document an early major meltwater episode during the Oldest Dryas th at suggests summer melting during this extreme cold period, inferred from high latitude northern hemisphere records [ Denton et al. 2005] Core Location and Methods Located in the northern GOM (Figure 2 1), appro ximately 300 km from the current Mississippi River delta, Orca Basin has an anoxic brine pool (salinity >250) that provides a laminated record of GOM paleoceanography. High sedimentation rates (~40 cm/1000 yrs) allow for high resolution sampling at nearly decadal resolution and abundant pteropod tests suggest negligible carbonate dissolution.

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27 Figure 2 1. Location Map of Orca Basin and the Laurentide Ice Sheet (LIS). Orca Basin is located approximately 300 km south southwest of the current Mississippi R iver Delta. The Laurentide Ice Sheet (LIS) and its extent at ~13 kcal yrs B.P. is also shown with its possible meltwater routes. Core MD02 2550 (9.09 m giant 25 cm 2 Calypso gravity core), recovered from 2248 m water depth (26¡56.78' N, 91¡20.75' W) by th e R/V Marion Dufresne in 2002, was sampled every half cm from core top to 466 cm, and every 1 cm to 908cm. All samples were freeze dried, wet sieved and washed over a 63 m mesh with deionized water. When available, approximately 60 70 individuals from both white and pink var ieties (separately) of the planktonic Foraminifera

PAGE 35

28 species Globigerinoides ruber were picked from the 250 355 m size fraction; many samples (particularly the white variety) had only 40 50 individuals. Once picked, samples were sonicated with methanol for 5 seconds to remove broken fossil particles from inside the G. ruber tests, dried and weighed. Each sample was split in half for stable isotopic and elemental analyses. Sub samples for isotopic analysis were pulverized for homogeneity and a 50 80 g aliq uot was analyzed on a ThermoFinnigan Delta Plus XL dual inlet mass spectrometer with an attached Kiel III carbonate preparation device at the College of Marine Science, University of South Florida. Smaller samples (<30 individuals) were crushed and prepar ed for elemental analyses after a 50 g aliquot of crushed material was taken for isotopic analysis. Isotopic data, 18 O C (Figure 2 2) and 13 C C calibrated with standard NBS 19, are reported on the VPDB scale. Long term analytical precision based on >10 00 NBS 19 standards is 0.06 for 18 O C and 0.05 for 13 C C

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29 2 2.5 3 3.5 4 4.5 5 5.5 Mg/Ca (mmol/mol) White G. ruber 2.5 3 3.5 4 4.5 5 Mg/Ca (mmol/mol) Pink G. ruber -5 -4 -3 -2 -1 0 18 O C ( VSMOW) Pink G. ruber -5 -4 -3 -2 -1 0 1 2 300 350 400 450 500 550 600 650 18 O C ( VSMOW) White G. ruber Depth (cm) Figure 2 2. Raw white and pink G. ruber data vs. depth from Core MD02 2550. (a) White G. ruber Mg/Ca data and (b) pink G. ruber Mg/Ca data. Average precision is 0.01 mmol/mol. (c) White G. ruber 18 O C and (d) pink G. ruber 18 O C Average precision is 0.06. Remaining sub samples (150 300 g) were lightly crushed between 2 glass plates and extensively cleaned for Mg/Ca analyses [ Barker et al. 2003] The Cambridge cleaning process includes multiple trace metal clean water and methanol rins es to remove clays, an oxidizing treatment with a buffered peroxide d c a b

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30 solution to remove organic material and a weak acid leach to remove adsorbed particles. Samples were then dissolved in a weak 0.075 N HNO 3 solution, diluted to a target calcium concentrat ion of ~ 25 ppm and analyzed on an Agilent Technologies 7500cx inductively coupled plasma mass spectrometer (ICP MS), installed in 2008 at the College of Marine Science, University of South Florida. Method development and sequence follow Williams et al., (2008). Instrumental precision for Mg/Ca is 0.01 mmol/mol, based on analyses of approximately 1500 reference standards, over the course of 16 runs. Average standard deviation of 37 white G. ruber replicate Mg/Ca analyses (17%) is 0.076 mmol/mol. Averag e standard deviation of 85 pink G. ruber replicate Mg/Ca analyses (29%) is 0.12 mmol/mol. SST was calculated using the Anand et al. (2003) calibration curve for white (Mg/Ca= 0.449 0.09*SST ) G. ruber This equation is also appropriate for pink G. ruber ba sed on core top and historical data from the Gulf of Mexico [ Richey et al. 2008] Clay removal and Mn Fe oxides were monitored by Al/C a and Mn/Ca ratios [ Barker et al. 2003; Lea et al. 2005; Pena et al. 2005; Williams et al. 2008] Data with Al/Ca ratios greater than 200 mol/mol (8% of both white and pink G. ruber samples, separately) were e liminated from plots as their Mg/Ca values may be influenced by excess Mg from possible clay contamination. All results are reported in Table A2 1; all Mn/Ca and culled Al/Ca data are displayed in Figure A2 1. There is no correlation between culled Al/Ca and Mg/Ca data for (r 2 = 0.05 for white G. ruber r 2 = 0.02 for pink G. ruber ). Although no Mn/Ca threshold was used to eliminate samples, there is also no correlation between Mn/Ca and Mg/Ca ratios (r 2 = 0.02 for white G. ruber r 2 = 0.01 for pink G. ruber ) Thirty four accelerator mass spectrometry (AMS) dates, between 308 and 614 cm, from monospecific G. ruber (white and pink varieties) provide the chronological control as reported in Williams et al (2008) (Figure A2 2).

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31 Meltwater Routing Hypothesis Th e G. ruber 18 O C record is affected by variations in calcification temperature and 18 O SW which is dependent on salinity and ice volume. The 18 O SW was isolated by removing the isotopic effects of temperature using the Orbulina unviersa high light equation (SST (¡ C=14.9 4.8(! 18 O C 18 O SW )) [ Bemis et al. 1998] A constant 0.27 was added to convert final 18 O SW values to the Vienna Standard Mean Ocean Water (VSMO W) scale. Isotopic effects of global ice volume [ Fairbanks 1989; Bard et al. 1990; Bard et al. 1996] was removed to specifically isolate changes in salinity and freshwater input from the Mississippi River (terme d 18 O GOM ) record. A relationship of 0.083 per 10 meters sea level change is used to subtract the isotopic effect of sea level [ Schrag et al. 2002] Overall, white and pink G. ruber 18 O GOM records display an isotopic decrease of approximately 3 from ~18.5 13.5 kcal yrs B.P. (Figure 2 3). Mean 18 O GOM values from 18.5 17.7 kcal yrs B.P. are approximately 1.2 and 0.3 for white and pink varieties, respectively. Both pink and whit e G. ruber varieties display similar multiple negative excursions of at least 1 through the deglaciation that suggest the presence of LIS and/or Glacial Lake Agassiz meltwater. The white G. ruber record exhibits 2 major excursions at ~16.4 15.7 kcal yrs B.P. (minimum 18 O GOM values: 1.0) and ~15.2 13.2 kcal yrs B.P. (minimum 18 O GOM values: 2.6). The pink G. ruber record displays 2 major negative excursions at ~16.5 15.8 kcal yrs B.P. (minimum 18 O GOM values: 1.4) and at ~15.2 13.1 kcal (minimum 18 O GOM values: 3.3).

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32 -3 -2 -1 0 1 2 18 O GOM ( VSMOW) White G. ruber modern 18 O GOM -4 -3 -2 -1 0 1 10 12 14 16 18 20 18 O GOM ( VSMOW) Pink G. ruber Calendar age (kcal yrs B.P.) -46 -44 -42 -40 -38 -36 -34 18 O ice ( VSMOW) NGRIP BllingAllerd Oldest Dryas Younger Dryas Figure 2 3. Comparison of (a) NGRIP 18 O ice to 18 O GOM of (b) white and (c) pink varieties of G. ruber As modern GOM 18 O GOM values are approximately +1, more negative values may be interpreted as periods where LIS meltwater dominates Miss issippi River water inout. Black triangles on the x axis represent 14 C dates. NGRIP data from [ Rasmussen et al. 2006] a b c

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33 As the white G. ruber MD02 2550 core top 18 O GOM value (+1.2) [ Flower and Quinn 2007] and Pigmy Basin zero age core top 18 O GOM values (+1.1) [ Richey et al. 2007] are in good agreement with the modern GOM values (+1.2) [ Fairbanks et al. 1992] any 18 O GOM values more negative than +1 are interpreted as influenced by isotopically depleted freshwater, including LIS meltwater. A simple version of the meltwater routing hypothesis states that meltwater should be present in the GOM during Greenland interstadials and not during stadials [ Clark et al. 2001] and is not supported in the early deglacial period during the Oldest Dryas event. The first major meltwater episode to the GOM occurs at approximately 16 .4 15.7 kcal yrs B.P. Pink G. ruber 18 O GOM data show a similar excursion from ~16.5 15.8 kcal yrs B.P. However, the onset of the Oldest Dryas in Greenland (~16.9 kcal yrs B.P.) occurs earlier than major melting, and the meltwater episode itself occurs during the Greenland stadial, which i s inconsistent with the meltwater routing hypothesis. Because the error associated with the calendar year calibration during this period is approximately 400 yrs, the earliest time that meltwater could have been routed south was at ~16.9 kcal. For the m eltwater routing hypothesis to be supported, meltwater would have needed to enter the GOM prior to 16.9 kcal yrs B.P., and then ceased at the onset of the Oldest Dryas. However, our evidence shows that meltwater prior to the Blling Allerd warm period ent ered the GOM at ~15.0 kcal yrs B.P. and continued until ~13.2 kcal yrs B.P. Although climate records from Greenland show multiple millennial scale cold periods during the last deglaciation, white and pink G. ruber 18 O GOM records do not show any increase in meltwater before the onset of these events, nor a cessation of meltwater during the events. White and pink G. ruber 18 O GOM records do support the meltwater routing hypothesis for the Younger Dryas event. Both pink and white records exhibit peak meltwa ter signals at ~ 13.4 kcal and 13.6 kcal yrs B.P., respectively followed by a cessation/reduction in meltwater at the onset of the GOM cooling

PAGE 41

34 inferred to reflect the Younger Dryas (Figure 2 2). Additionally the cessation of meltwater coincides with the onset of the Younger Dryas in Cariaco Basin and with Greenland ice core records [ Williams et al ., in preparation ] (Figure 2 4). The Younger Dryas event ~12.9 11.7 kcal yrs B.P. appears to be a high salinity interv al based on 18 O GOM from white and pink G. ruber Mean white G. ruber values of ~ +1.2 suggest a complete cessation of meltwater. 0 20 40 60 80 100 14 C ( VSMOW Detended) Cariaco Basin 11,66050 10,97050 11,28040 12,24050 -3 -2 -1 0 1 2 18 O GOM ( VSMOW) GOM White G. ruber 12,08540 11,17060 11,37540 11,57550 -4 -3 -2 -1 0 1 12.5 13 13.5 14 18 O GOM ( VSMOW) GOM Pink G. ruber Calendar Age (kcal yrs B.P.) Figure 2 4. The Younger Dryas cessation event. The rapid change in THC strength, inferred from Cariaco Basin # 14 C [ Hughen et al. 2000] is nearly synchronous with the cessation of meltwater in the GOM. Raw radiocarbon 14 C dates are also included.

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35 There is strong eviden ce for large changes in THC coinciding with periods of abrupt climate change during the deglacial period [ Boyle and Keigwin 1987; Boyle 1988; Keigwin and Lehman 1994; Hughen et al. 2000; McManus et al. 2004; Hug hen et al. 2006] Cd/Ca ratios of benthic Foraminifera, a proxy for inorganic phosphorus concentrations, show an abrupt reduction in NADW formation during the Oldest Dryas from approximately 16.0 to 15.0 kcal yrs B.P. on the Bermuda Rise [ Boyle and Keigwin 1987] 231 P a/ 230 Th ratios provide a quantitative THC record extending to approximately 20.0 kcal yrs B.P at the LGM, when overturning circulation was reduced 30 40% compared to late Holocene strength. The deglacial period exhibits high THC variability, including a nearly instantaneous", complete THC shutdown spanning Heinrich Event 1 (H1) at approximately 17.5 15.0 kcal yrs B.P. [ McManus et al. 2004] All THC proxies show excursions suggesting a reduction in THC at the onset of the Younger Dryas. 231 Pa/ 230 Th and Cd/Ca display significant changes in THC strength during the Younger Dryas, yet with only a partial reduction in THC strength [ Boyle and Keigwin 1987; McManus et al. 2004] 231 Pa/ 230 Th ra tios show thermohaline strength reduction initiating at 12.7 kcal yrs B.P. and lasting for approximately 500 years before increasing to modern Holocene values. It is possible that a larger reduction did occur during the Younger Dryas, but that the 231 Pa/ 2 30 Th record was unable to resolve such a rapid change in THC before resuming to more decreased values associated with stronger circulation [ McManus et al. 2004] In comparison, a large increase in # 14 C based on Cariaco Basin sediments at the onset of the Younger Dryas suggests a rapid decrease in THC (70% compared to modern day) with a raw radiocarbon midpoint date at 11.28 0.040 14 C kcal yrs B.P. (12.87 kcal yrs B.P.). # 14 C values decrease sl owly through the Younger Dryas with a slight rate increase at the Younger Dryas termination at approximately 11.4 kcal yrs B.P. [ Hughen et al. 2000] When compared to the raw radiocarbon date of the GOM cessation event (11.575 50 14 C kcal yrs B.P.), the midpoint of the reduction in NADW in

PAGE 43

36 the # 14 C record (11.280 0.040 14 C kcal yrs B.P.) occurs nearly synchronously (Figure 2 4) [ Hughen et al. 2000] Glacial Lake Agassiz may have been a source of GOM meltwater after 13.67 kcal yrs B.P. (11.81 14 C kcal yrs B.P.) [ Lepper et al. 2007] As the LIS receded from its southernmost position, glacial moraines such as the Big Stone Moraine, located at the junction between western Minnesota, North Dakota and South Dakota, rem ained as major geomorphologic features. Big Stone Moraine formed at approximately 14.0 kcal yrs B.P. as the second major recessional position of the Des Moines lobe of the LIS [ Lepper et al. 2007] (1 st position is the Bemis Moraine at 16.25 kcal yrs B.P. [ Lowell et al. 1999] ). As the Des Moines lobe retreated (~270m/yr at the onset of th e Blling Allerd), proglacial Lake Agassiz formed, constrained by the LIS in the north and Big Stone Moraine in the south beginning at approximately 13.67 kcal yrs B.P. (11.81 14 C kcal yrs B.P.) [ Lepper et al. 2007] During its ~5000 yr life span, Lake Agassiz occupied a region that included parts of Saskatchewan, Manitoba, Ontario, QuŽbec, North Dakota, South Dakota and Minnesota before its final drainage around 7.5 14 C kcal yrs B.P. There were 5 main phases of Lake Agassiz: Lockhart, Moorhead, Emerson, Nipigon and Ojibway [ Fenton et al. 1983; Teller and Thorleifson 1983] The Lockhart phase extends from lake inception (13.67 kcal yrs B.P.) until approximately 11.0 14 C kcal yrs B.P., when lake levels abruptly fell at the onset of the Moorhead phase (appro ximately 11.0 14 C kcal yrs B.P. to 10.1 14 C kcal yrs B.P.) [ Teller and Thorleifson 1983; Leverington et al. 2002] Three major beaches, at elevations higher than the southern outlet (Herman, Upham and Norcross strandlines) indicate only a 14 m drop in lake level before the onset of the Moorhead phase [ Lepper et al. 2007] The onset of the Moorhead phase at approximately 11. 0 14 C kcal yrs B.P. marks a 110 meter lake level drop associated with an estimated volume of 9500 km 3 according to the model used by Leverington (2000). Teller and Thorleifson (1983) suggest the lake level drop may have occurred over a 2 year period.

PAGE 44

37 Ev idence from sediment cores taken from the southern outlet of Lake Agassiz show a change from an active to abandoned spillway at the end of the Lockhart phase at 10.8 14 C kcal yrs B.P. [ Fisher 2003] Many hypothesize that Lake Agassiz meltwater was routed east through the Lake Superior basin which was located at a much lower outlet than the southern outlet [ Teller et al. 2005] Although Lake Agassiz meltwater may have played a significant role in meltw ater routing after its inception at ~13.7 kcal yrs B.P. [ Lepper et al. 2007] 18 O GOM cannot distinguish Lake Agassiz water from LIS input. In summary, the meltwater routing hypothesis is strongly supported during the Younger Dryas interval, but not for earlier abrupt climate events. New 18 O GOM results combined with # 14 C measureme nts from Cariaco Basin suggest that the cessation event coincided with the rapid decrease in THC. The timing of southern meltwater and its cessation at 12.9 kcal yrs B.P. is consistent with the rerouting of Lake Agassiz/LIS meltwater and the subsequent re duction of NADW. Our 18 O GOM results do not support the meltwater routing hypothesis during the Oldest Dryas is seen in the middle of the event beginning at ~ 16.4 kcal yrs B.P. Changes in Seasonality During the Last Deglaciation Evidence for enhanced seasonality during stadi als is found in comparing Greenland ice core records and lateral moraines as well as in European lake sediments and fossil beetle records [ Atkinson et al. 1987; Denton et al. 2005] Temperature reconstruction through fossilized beetles, based on climate tolerances of 350 beetles at 26 sites on the British Isles indicates increased seasonality. Beetle records also imply enhanced seasonality during the Oldest Dryas with winter temperatures as cold as 20 to 25¡C and summer conditions as warm as 1 0¡C. Supporting lacustrine and fossil records from Europe suggest that not only were Greenland stadials periods of increased seasonality, but that the Blling Allerd warm period was an interval of reduced seasonality, similar to modern day. Air temperat ure estimates reconstructed from beetle assemblages suggest that minimum Blling Allerd winter temperatures were approximately 0

PAGE 45

38 5¡C and maximum summer temperatures were approximately 17 18¡C. Younger Dryas winters were estimated at 25¡C and summer tempe ratures were as warm as 10¡C [ Atkinson et al. 1987] The GOM 18 O GOM data sets provide a detailed record of inferred summer melting of the LIS during the last deglaciation. A corollary of Denton et al.'s (2005) seasonality hypothesis is that summers may have been warm enough, even during stadial events, to allow fo r summer melting of high latitude northern hemisphere ice sheets. The white G. ruber 18 O GOM data set exhibits a major meltwater episode (mean 18 O GOM = 0.14) during the Oldest Dryas at ~16.4 15.7 kcal yrs B.P. Pink G. ruber 18 O GOM data show a similar excursion (mean 18 O GOM = 0.76) at ~16.5 15.8 kcal yrs B.P. Our data confirms the presence of meltwater before the onset of the Blling Allerd warm period as early as ~16.4 kcal yrs B.P. during the Oldest Dryas. We infer that increased seasonality ass ociated with NADW reduction and the formation of sea ice in the North Atlantic during cold winters was also associated with summer temperatures sufficiently high for ice sheet melting. Summer melting of high latitude ice sheets may have been a critical pre requisite for extensive sea ice formation during the Oldest Dryas and Younger Dryas intervals. Summer melting may have sufficiently reduced salinity to allow extensive sea ice formation in succeeding winters and reduced NADW formation. Possible sources of meltwater supply to the North Atlantic may have been Greenland, the Arctic, or the LIS. It is also possible that southern routed LIS meltwater (via the Gulf Stream) may have pre conditioned the North Atlantic for extensive winter sea ice formation. GOM S ST results exhibit multiple high frequency SST changes through out the deglacial period and may be influenced by seasonality changes. In comparison to Greenland ice cores and European lake sediments, three major abrupt climate events are resolved in the w hite G. ruber GOM SST record that may be correlative with the Oldest Dryas (16.0 14.7 kcal yrs B.P.), Blling Allerd (14.7 12.9 kcal), and the Younger Dryas (12.9 11.7 kcal) [ Williams et al.,

PAGE 46

39 in preparation]. Pink G. ruber exhibits a SST increase from ~1 7.8 14.6 kcal yrs B.P. (~4.5¡C increase) followed by a ~2¡C cooling with coldest temperatures at ~14.0 kcal yrs B.P. before increasing again (Figure 2 5). SSTs continue to increase until ~13.6 kcal (~2.7¡C SST increase), and then decrease to 22.7¡C at 12. 6 kcal yrs B.P. From 12.6 12.1 kcal, SST increases (~2.2¡C increase), followed by a slight decrease (~1.5¡C) at ~11.9 11.4 kcal yrs B.P.

PAGE 47

40 -46 -44 -42 -40 -38 -36 -34 18 O ice ( VSMOW) NGRIP Younger Dryas BllingAllerd Oldest Dryas a -4 -2 0 2 4 SST (¡C) Seasonality increase b 18 20 22 24 26 28 Mg/Ca-SST (¡C) White G. ruber c 10 12 14 16 18 20 20 21 22 23 24 25 26 Mg/Ca-SST (¡C) Pink G. ruber Calendar Age (kcal yrs B.P.) d Figure 2 5. Comparison of (a) NGRIP 18 O ice to (b) #SST (calculated by subtracting white G. ruber SST from pink G. ruber SST), (c) white G. ruber Mg/Ca SST, and (d) pink G. ruber Mg/Ca SST. Average precision based on replicate analyses is 0.3 ¡C for white G. ruber and 0.5 ¡C in pink G. ruber NGRIP data from [ Rasmussen et al. 2006]

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41 Although the seasonal distribution of white and pink varieties of G. ruber are unknown in the GOM, Sargasso Sea sediment trap data suggest that while both varieties are more prevalent during summer months, the pink variety is primarily a non winter species and white G. ruber i s present all year [ Deuser et al. 1981; Deuser 1987; Deuser and Ross 1989] Plankton tows in the northern GOM indicate both varieties live in the upper 50 m [ BŽ and Hamlin 1967] With t he assumption that the seasonal and depth distribution of G. ruber varieties were similar in the GOM through the deglacial period, we compare Mg/Ca SST results from the pink and white varieties of G. ruber to infer changes in seasonality. Differencing the white G. ruber SST record from the pink SST record (termed #SST (¡C)), we can estimate the timing and magnitude of seasonality changes in the GOM. If the SST divergences between pink and white varieties of G. ruber are due to the difference in seasonal di stribution, intervals with large positive temperature differences may reflect an increase in seasonality (Figure 2 5). Because the white G. ruber species is thought to inhabit the GOM all year (summer weighted), #SST values should represent minimum seaso nal differences. Although both records show a similar SST increase from ~18.5 16.4, during the latter part of the Oldest Dryas from ~16.0 14.7 kcal yrs B.P., temperatures reflected in the white G. ruber exhibits a 2¡C cooling [ Williams et al., in preparati on] while the non winter SSTs (pink variety) displays little change. The Oldest Dryas interval (16.9 14.7 kcal yrs B.P.) displays a mean #SST of +1.34¡C with maximum #SST values (~3.5¡C) at the Oldest Dryas/Blling Allerd transition (14.7 kcal yrs B.P.). Seasonality decreases rapidly at the onset of the Blling Allerd warm period. The Blling Allerd is marked by a white G. ruber SST increase of approximately 3.5¡C, while the pink variety exhibits a cooling of ~2.0¡C. This large divergence suggests tha t while summer temperatures may have cooled,

PAGE 49

42 winters were relatively mild, decreasing seasonal differences. Blling Allerd seasonality also appears to be similar to that of the earliest Holocene. The Younger Dryas interval (12.9 11.7 kcal yrs B.P.) exhib its a mean #SST of 1.1¡C with maximum #SST of ~3.0¡C at 11.8 kcal yrs B.P. During the Younger Dryas, both pink and white G. ruber SSTs decreased initially at ~12.9 kcal yrs B.P., but the pink record exhibits a significant warming throughout most of the Yo unger Dryas interval, where white G. ruber SSTs remain cool. Inferred from the pink and white SST diversion, the Younger Dryas interval may have had anomalously cold winters and warm summers. #SST data are consistent with seasonality changes in the northe rn North Atlantic region. Higher #SST values during the Oldest and Younger Dryas suggest large seasonal temperature differences during deglacial stadials. Additionally, the Blling Allerd warm period exhibits #SST similar to the earliest Holocene, sugge sting decreased seasonality. Our findings suggest that enhanced seasonality during the Oldest Drays and Younger Dryas extended well beyond the northern North Atlantic region at least to the northern GOM. Conclusion Overall, the last deglaciation was a dy namic period with significant SST and seasonality changes, which may have influenced northern hemisphere LIS melting. Our data provide the first detailed evidence, with paired white and pink G. ruber stable isotope and Mg/Ca SST analyses and excellent AMS 14 C age control, of the cessation of meltwater at the onset the GOM. The cessation event (11.575 0.50 14 C kcal yrs B.P.) coincides with the decrease in THC (derived from the Cariaco Basin # 14 C record), based on direct comparison of raw 14 C ages, which is consistent with the suggestion that NADW formation was reduced by a re routing of LIS and/or Lake Agassiz meltwater and caused the Younger Dryas event. White and pink G. ruber 18 O GOM exhibit at least 2 major meltwater episodes with excursions of at lea st 1 at ~16.4 15.7 and ~15.2 13.2 kcal yrs

PAGE 50

43 B.P. The presence of meltwater from 16.4 kcal yrs B.P. during the Oldest Dryas is consistent with enhanced seasonality documented in the northern North Atlantic region. Comparison of paired white and pink G. ru ber Mg/Ca SST may indicate increased seasonality in the GOM during the Oldest Dryas and Younger Dryas. Our results suggest a corollary of Denton et al.'s (2005) seasonality hypothesis that summers may have been warm enough, even during stadial events, to allow for summer melting of high latitude northern hemisphere ice sheets.

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49 Hughen, K. A., M. G. L. Baillie, E. Bard, W. J. Beck, C. J. H. Bertrand, P. G. Blackwell, C. E. Buck, G. S. Burr, K. B. Culter, P. E. Damond, R. L. Edwards, R. B. Fairbanks, M. Friedrich, T. P. Guilderson, P. J. Reimer, R. W. Reimer, S. Remmele, J. R. Southon, M. Stuiver, T. Sahra, F. W. Taylor, J. van der Plicht, and C. E. Weyhenmeyer (2004), Mar ine04 Marine Radiocarbon Age Calibration, 0 26kyr B.P., Radiocarbon 46 (3), 1059 1086. Jouzel, J., V. Masson, O. Cattani, S. Falourd, M. Stievenard, B. Stenni, A. Longinelli, S. J. Johnsen, and N. I. Barkov (2001), A new 27 ky high resolution East Antarct ic climate record, Geophysical Research Letters 28 (16), 3199 3202. Keigwin, L., and S. J. Lehman (1994), Deep circulation change linked to HEINRICH event 1 and Younger Dryas in a middepth North Atlantic core, Paleoceanography 9 (2), 185 194. Kennett, J. P., and N. J. Shackleton (1975), Laurentide Ice Sheet Meltwater Recorded in Gulf of Mexico Deep Sea Cores, Science 188 (4184), 147 150. Lea, D. W., D. K. Pak, L. C. Peterson, and K. A. Hughen (2003), Synchroneity of Tropical and High Latitude Atlantic Te mperatures over the Last Glacial Termination, Science 301 1361 1364. Lea, D. W., D. K. Pak, and G. Paradis (2005), Influence of volcanic shards on foraminiferal Mg/Ca in a core from the Gal‡pagos region, Geochemistry, Geophysics, Geosystems 6 (11). Lep per, K., T. G. Fisher, I. Hajdas, and T. V. Lowell (2007), Ages for the Big Stone Moraine and the oldest beaches of glacial Lake Agassiz: Implications for deglaciation chronology, Geology 35 (7), 667 670. Leverington, D. W., J. D. Mann, and J. T. Teller ( 2002), Changes in the Bathymetry and Volume of Glacial Lake Agassiz between 9200 and 7700 14 C yrs B.P., Quaternary Research 57 244 252. Lowell, T. V., R. K. Hayward, and G. H. Denton (1999), Role of climate oscillations in determining ice margin positio n: Hypothesis, examples and implications, in Glacial processes past and present edited by D. M. Mickelson and J. W. Attig, pp. 193 203. Lowell, T. V., T. G. Fisher, G. C. Comer, I. Hajdas, N. Waterson, K. Glover, H. M. Loope, J. M. Schaefer, V. Rinterkne cht, W. S. Broecker, G. H. Denton, and J. T. Teller (2005), Testing the Lake Agassiz Meltwater Trigger for the Younger Dryas, EOS, American Geophysical Union 86 (40), 365 373.

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50 Manabe, S., and R. J. Stouffer (1997), Coupled ocean atmosphere model response t o freshwater input: Comparison to Younger Dryas event, Paleoceanography 12 321 336. Mayewski, P. A., M. L.D., M. S. Twickler, S. Whitlow, Q. Yang, W. B. Lyons, and M. Prentice (1997), Major features and forcing of high latitude northern hemisphere atmos pheric circulation using a 110,000 year long glaciochemical series, Journal of Geophysical Research 102 26345 26366. McManus, J. F., R. Francois, J. M. Gherardi, L. D. Keigwin, and S. Brown Leger (2004), Collapse and rapid resumption of Atlantic meridio nal circulation linked to deglacial climate changes, Nature 428 834 837. Morgan, V., M. Delmotte, T. v. Ommen, J. Jouzel, J. Chappellaz, and D. Raynaud (2002), Relative Timing of Deglacial Climate Events in Antarctica and Greenland, Science 297 1862 1 864. Pena, L. D., E. Calvo, I. Cacho, S. Eggins, and C. Pelejero (2005), Identification and removal of Mn Mg rich contaminant phases on foraminiferal tests: Implications for Mg/Ca past temperature reconstructions Geochemistry, Geophysics, Geosystems 6 (9) Pilcher, R. S., and R. D. Blumstein (2007), Brine volume and salt dissolution rates in Orca Basin, northeast Gulf of Mexico, AAPG Bulletin 91 (6), 823 233. Rasmussen, S. O., K. K. Andersen, A. M. Svensson, J. P. Steffensen, B. M. Vinther, H. B. Clausen M. L. Siggaard Anersen, S. J. Johnsen, L. B. Larsen, D. Dahl Jensen, M. Bigler, R. Ršthlisberger, H. Fischer, K. Goto Azuma, M. E. Hansson, and U. Ruth (2006), A new Greenland ice core chronology for the last glacial termination, Journal of Geophysical R esearch 111 1 15. Reimer, P. J., M. G. L. Baillie, E. Bard, A. Bayliss, W. J. Beck, C. J. H. Bertrand, P. G. Blackwell, C. E. Buck, G. S. Burr, K. B. Culter, P. E. Damond, R. L. Edwards, R. B. Fairbanks, M. Friedrich, T. P. Guilderson, A. G. Hogg, K. A. Hughen, B. Kromer, G. McCormac, S. Manning, C. B. Ramsey, R. W. Reimer, S. Remmele, J. R. Southon, M. Stuiver, S. Talamo, F. W. Taylor, J. van der Plicht, and C. E. Weyhenmeyer (2004), INTCAL04 Terrestrial Radiocarbon Age Calibration, 0 26kyr B.P., Radioc arbon 46 (3), 1029 1058. Richey, J. N., R. Z. Poore, B. P. Flower, and T. M. Quinn (2007), 1400 yr multiproxy record of climate variability from the northern Gulf of Mexico, Geology 35 (5), 423 426.

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51 Richey, J. N., R. Z. Poore, and D. J. Hollander (2008 ), Reproducibility of a High Resolution, Late Holocene Foraminiferal Mg/Ca Record from the Gulf of Mexico, Eos, Transactions of the America Geophysical Union 89 (53), Fall Meet. Suppl., Abstract PP14B 03. Rooth, C. (1982), Hydrology and ocean circulation, Progressive Oceanography 11 131 149. Ruddiman, W. F. (1977), Late Quaternary deposition of ice rafted sand in the subpolar North Atlantic (lat. 40¡ to 65¡N), Geological Society of America Bulletin 88 1813 1827. RŸhlemann, C., S. Mulitza, P. J. MŸlle r, G. Wefer, and R. Zahn (1999), Warming of the tropical Atlantic Ocean and slowdown of thermohaline circulation during the last deglaciation, Nature 402 511 514. Sackett, W. M., B. B. Bernard, and J. M. Brooks (1977), Chemical measurments in Orca Basin sediments:, Eos, Transactions of the America Geophysical Union 58 1175 Schaefer, J. M., G. H. Denton, D. J. A. Barrell, S. Ivy Ochs, P. W. Kubik, B. G. Andersen, F. M. Philips, T. V. Lowell, and C. SchlŸchter (2006), Near Synchronous Interhemispheric Termination of the Last Glacial Maximum in Mid Latitudes, Science 312 1510 1513. Schrag, D. P., J. F. Adkins, K. McIntyre, J. L. Alexander, D. A. Hodell, C. D. Charles, and J. F. McManus (2002), The oxygen isotopic composition of seawater during the La st Glacial Maximum, Quaternary Science Reviews 21 331 342. Severinghaus, J. P., T. Sowers, E. J. Brook, R. B. Alley, and M. L. Bender (1998), Timing of abrupt climate change at the end of the Younger Dryas interval from thermally fractionated gases in p olar ice, Nature 391 141 146. Severinghaus, J. P., and E. J. Brook (1999), Abrupt Climate Change at the End of the Last Glacial Period Inferred from Trapped Air in Polar Ice, Science 286 930 934. Shokes, R. F., P. K. Trabant, B. J. Presley, and D. F. Reid (1977), Anoxic hypersaline basin in the northern Gulf of Mexico, Science 196 1443 1446. Stocker, T. F. (2000), Past and future reorganization in the climate system, Quaternary Science Reviews 19 301 319.

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52 Stuiver, M., P. J. Reimer, E. Bard, W. J Beck, G. S. Burr, K. A. Hughen, B. Kromer, G. McCormac, J. v. d. Plicht, and M. Spurk (1998), INTCAL98 radiocarbon age calibration, 24,000 0 cal B.P., Radiocarbon 40 (3), 1041 1083. Tarasov, L., and W. R. Peltier (2005), Arctic freshwater forcing of the Younger Dryas cold reversal, Nature 435 Teller, J. T., and L. H. Thorleifson (1983), The Lake Agassiz Lake Superior connection, in Glacial Lake Agassiz edited by J. T. Teller and L. Clayton, pp. 261 290. Teller, J. T., M. Boyd, Z. Yang, P. S. G. Kor, and A. M. Fard (2005), Alternative routing of Lake Agassiz overflow during the Younger Dryas: new dates, paleotopograpy, and a re evaluation, Quaternary Science Reviews 24 1890 1905. Waelbroeck, C., J. C. Duplessy, E. Michel, L. Labeyrie, D. Paillard, and J. Duprat (2001), The timing of the last deglaciation in North Atlantic climate records, Nature 412 724 727. Wagner, A., T. P. Guilderson, S. Niall, and J. E. Cole (In press), Pre Bomb Surface Water Radiocarbon of the Gulf of Mexico and Caribbean a s Recorded in Hermatypic Corals, Radiocarbon Williams, C., B. Flower, D. Hastings, and R. N. (2008), Meltwater and Abrupt Climate Change in the Gulf of Mexico During the Last Gacial Termination, Eos, Transactions of the America Geophysical Union 89 (53), Fall Meet. Suppl., Abstract PP21C 1442.

PAGE 60

53 Appendix 1: Chapter One Figures

PAGE 61

5 4 Appendix 1. Table A1 1. White G. ruber Mg/Ca, Al/Ca and Mn/Ca data from MD02 2550. Sample Depth (cm) Mg/Ca (mmol/mol) Al/Ca (mol/mol) Mn/Ca (mol/mol) 311 3.95 42.24 539.96 312 4.04 127.40 431.48 312.5 4.03 40.49 445.40 313 4.26 46.30 434.13 314 3.99 67.53 736.52 314.5 3.94 67.52 837.06 315 3.93 191.54 1,007.31 315.5 5.04 971.58 a 785.45 316 3.44 121.68 847.11 317 4.14 80.08 802.33 317.5 4.12 58.25 727.85 318.5 4.00 29.57 665.37 318 4.04 21.32 642.96 319 4.43 162.30 720.00 319.5 4.31 56.83 850.89 320 4.18 142.71 864.64 320 4.31 138.01 820.98 320.5 4.26 1,118.62 884.39 321.5 4.00 47.89 682.20 322.5 4.14 Below Detection Limit 645.90 323 4.03 68.29 622.15 323.5 4.30 54.96 593.03 324 5.24 163.64 553.68 325.5 4.59 42.02 500.61 329.5 3.89 2.95 669.14 330.5 3.86 49.96 704.56 331 3.80 80.21 680.76 331.5 3.76 225.20 849.51 332 3.88 70.09 739.01 333 4.43 90.83 542.30 336 3.88 112.55 717.64 336.5 4.31 Below De tection Limit 558.92 337 4.29 125.09 891.48 337.5 3.74 Below Detection Limit 896.97 338 3.47 49.48 782.13 338.5 3.88 2.73 841.33 340.5 3.53 35.99 609.28 341 3.62 92.29 558.31 341.5 3.64 56.26 676.97

PAGE 62

55 Appendix 1 (Continued). Table A1 1 (Continued) 3 42 3.21 66.18 478.55 343.5 3.39 12.23 930.70 345.5 3.92 Below Detection Limit 679.44 346 3.42 5.43 770.58 346.5 3.31 Below Detection Limit 790.56 347 3.54 104.55 649.70 347.5 3.76 Below Detection Limit 541.02 349 3.52 35.36 599.70 349.5 3.44 87.39 520.92 351 3.86 58.82 521.33 351.5 3.37 61.00 483.54 353 3.46 Below Detection Limit 765.62 353.5 3.59 45.63 613.39 354 3.68 Below Detection Limit 633.57 355 3.29 13.96 841.36 356 3.18 51.55 1,032.30 357 3.26 38.62 777.10 358 3.90 57.97 538.76 35 8.5 3.99 70.73 711.11 359.5 3.49 Below Detection Limit 752.11 360.5 4.12 1,669.05 549.40 364.5 3.41 221.10 989.32 368 3.61 80.76 766.41 372 3.67 82.46 821.51 375.5 3.76 87.39 1,008.63 379 4.17 33.68 518.77 380 3.94 64.09 389.77 380.5 3.25 0.28 1,3 39.63 385 4.23 114.93 1,221.25 385.5 4.02 31.12 1,156.89 392 4.20 28.36 392.42 393 4.16 48.86 294.87 394 3.67 26.24 226.97 396.5 3.43 28.08 203.06 397 3.96 13.88 174.14 397.5 4.26 78.31 203.54 398 4.29 59.54 214.93 398.5 3.88 37.77 171.38 398 4. 24 33.06 280.06 399 3.76 48.13 226.84 399.5 3.69 60.92 213.10

PAGE 63

56 Appendix 1 (Continued). Table A1 1 (Continued) 400 3.87 Below Detection Limit 183.29 401 3.09 30.24 210.46 401.5 4.10 42.26 166.81 410 3.48 24.56 142.27 412 3.72 22.04 152.24 413 4.14 2 5.93 170.70 414 3.28 34.16 151.78 417.5 4.37 16.15 170.95 420 4.36 126.98 178.87 421 4.86 120.11 154.60 421.5 4.19 143.51 147.94 421.5 4.18 33.04 164.87 422 4.52 108.91 180.45 422.5 4.08 289.48 203.67 423 4.19 62.46 156.19 423 4.32 16.42 142.09 424 4.00 22.78 182.80 425 3.99 173.76 147.92 425.5 3.97 38.94 120.41 426.5 4.65 30.65 161.57 427 4.22 38.66 160.23 430 4.23 34.71 183.64 455 3.60 24.29 200.72 455 3.74 73.37 234.36 455.5 3.75 17.68 171.48 456 3.64 31.93 177.51 456.5 3.43 20.21 18 1.75 458 3.45 23.44 195.22 458.5 3.50 13.21 181.18 459 3.72 13.17 220.75 459.5 3.87 18.71 177.75 460 3.23 22.10 185.84 460.5 3.49 21.64 147.71 461 3.56 21.60 159.71 461.5 3.34 183.19 172.22 462 3.44 19.64 191.40 462.5 3.35 40.65 179.64 463 3.48 27.42 159.51 464 3.38 15.96 196.04 464.5 3.52 26.94 187.79 465.5 3.46 Below Detection Limit 141.62

PAGE 64

57 Appendix 1 (Continued). Table A1 1 (Continued) 465.5 3.58 20.62 173.59 466 3.28 45.17 188.68 466 3.56 1.25 157.93 467 3.26 6.21 154.90 468 3.25 15.3 6 158.85 468 3.37 159.30 145.37 468 3.24 12.51 160.14 469 3.42 4.02 148.46 470 3.26 2.05 147.44 470 3.17 3.23 147.94 471 3.34 3.33 119.19 471 3.39 5.80 143.95 472 3.35 544.46 159.66 472 3.22 Below Detection Limit 157.29 473 3.60 4.18 170.47 473 3.61 2.70 165.14 473 3.57 Below Detection Limit 177.53 474 3.93 5.05 156.42 474 3.58 12.81 143.90 475 3.49 2.35 151.02 475 3.45 85.84 151.69 476 3.30 Below Detection Limit 155.31 476 3.19 11.47 142.30 477 3.21 4.29 157.35 477 3.32 Below Detection Limit 180.17 477 3.22 Below Detection Limit 153.74 478 3.51 Below Detection Limit 161.74 478 3.45 5.55 138.24 479 3.33 Below Detection Limit 160.53 479 3.37 20.28 127.75 480 3.10 Below Detection Limit 156.54 480 3.25 9.70 159.41 481 3.21 11.50 146. 00 481 3.33 203.49 149.67 481 3.27 Below Detection Limit 148.43 482 3.52 Below Detection Limit 163.39 482 3.52 4.98 158.75 483 3.74 3.87 165.46 484 3.54 3.38 153.51 485 3.81 4.60 184.29 486 3.42 23.63 180.66

PAGE 65

58 Appendix 1 (Continued). Table A1 1 (Con tinued) 488 3.38 Below Detection Limit 207.68 488 3.63 7.12 169.42 490 3.62 49.70 181.60 490 3.39 24.22 138.84 492 3.29 301.16 137.61 492 3.34 20.95 130.48 493 3.47 10.04 142.56 494 3.24 58.59 132.38 495 3.50 22.25 154.96 495 3.51 166.88 156.64 496 3.44 38.13 166.44 497 3.29 50.54 114.15 498 3.40 6.43 148.70 498 3.44 15.87 142.41 499 3.41 8.60 135.87 500 2.13 13.14 129.98 500 3.22 5.65 131.63 501 3.52 18.48 115.37 501 3.35 7.28 121.47 503 3.52 18.46 143.70 505 3.18 11.67 113.42 506 3.5 3 12.13 133.25 507 3.22 14.80 148.14 508 3.42 367.85 125.58 510 3.23 14.86 131.85 511 3.84 19.52 163.28 512 3.28 37.81 134.98 513 3.47 39.92 153.93 514 3.48 54.19 120.11 514 3.50 52.49 121.98 515 3.53 285.01 91.58 517 3.61 346.14 168.28 518 3.15 45.22 135.28 519 3.40 86.84 199.74 520 3.97 22.84 137.70 521 3.69 61.80 147.57 522 3.55 151.38 138.98 523 3.30 Below Detection Limit 125.22 524 3.76 10.23 192.19 525 3.77 72.14 178.01 526 3.85 71.25 155.91

PAGE 66

59 Appendix 1 (Continued). Table A1 1 (Cont inued) 527 3.39 5.02 152.53 528 3.72 617.43 152.87 529 3.98 Below Detection Limit 210.75 530 3.62 83.91 162.59 531 3.34 1,415.33 182.03 533 3.53 59.85 223.58 534 4.54 207.68 251.45 536 3.86 85.67 191.02 537 3.91 78.90 202.53 538 3.17 4.41 245.64 539 3.41 49.02 227.15 541 3.35 54.19 289.01 542 3.46 58.10 411.63 543 3.15 1,683.21 672.37 545 3.48 63.81 1,004.72 546 3.59 Below Detection Limit 726.16 547 3.08 79.87 452.20 550 3.45 66.67 328.28 551 3.66 357.70 314.75 552 3.47 21.75 292.02 553 3.29 7.25 272.57 554 3.31 22.56 312.20 554 3.18 Below Detection Limit 271.71 555 3.54 133.79 371.40 558 3.05 45.70 363.59 559 3.33 135.08 400.47 560 3.13 358.41 412.30 563 3.01 Below Detection Limit 561.39 568 3.51 41.31 983.49 569 3.08 Below Det ection Limit 1,011.37 570 3.14 2.36 956.00 571 2.86 3.21 1,050.24 572 2.93 2.80 1,100.56 572 2.70 75.00 987.80 573 3.03 50.91 1,146.54 577 3.13 92.58 869.87 578 2.92 220.46 819.76 579 3.22 58.97 900.58 580 2.96 89.98 792.41 580 2.94 1.24 812.68 581 2.80 90.53 863.20

PAGE 67

60 Appendix 1 (Continued). Table A1 1 (Continued) 582 3.04 63.11 936.92 583 2.74 53.51 985.80 585 2.82 76.35 894.14 588 3.03 48.19 906.35 589 2.86 68.91 759.54 590 3.18 50.18 738.94 591 2.76 48.28 615.54 592 3.23 176.27 573.14 593 2.70 217.85 621.60 597 2.68 43.72 888.58 597 2.69 1.73 736.84 598 2.39 37.18 765.24 599 2.61 38.95 678.33 600 2.33 49.43 606.17 601 2.24 Below Detection Limit 457.53 601 2.36 48.10 530.20 602 2.52 53.08 533.51 603 2.49 97.79 515.46 607 2.78 1 3.36 572.33 607 2.53 107.43 632.24 610 2.41 53.55 465.40 611 2.40 44.82 441.48 612 2.54 30.87 683.94 613 2.45 Below Detection Limit 593.54 613 2.49 25.25 577.68 617 2.31 39.32 332.21 618 2.70 68.99 419.89 619 2.61 44.92 461.70 620 2.48 28.16 367. 97 621 2.69 70.38 499.00 a Al/Ca ratios in red indicate value exceeds 200 mol/mol threshold; corresponding Mg/Ca measurements have been removed from data set analysis.

PAGE 68

61 Appendix 1 (Continued). Figure A1 1. Comparison of culled Mg/Ca and Al /Ca. The lack of correlation between Mg and Al suggests that Mg/Ca values are not influenced by insufficient clay removal. Figure A1 2. Comparison of culled Mg/Ca and Mn/Ca data. The lack of correlation between Mg and Mn suggesting that Mg/Ca values are not influenced by Mn overgrowths.

PAGE 69

62 Appendix 1 (Continued). Figure A1 3. Comparison of all Mg/Ca and weight per Foraminifera data.

PAGE 70

63 Appendix 1 (Continued). Table A1 2. Radiocarbon age control for core MD02 2550. Depth (cm) CAMS ID 14 C age 14 C error 2 sigma calendar age (lower) 2 sigma calendar age (upper) Median probability calendar age 308 100676 9,385 a 40 10540 10789 10,639 318 139344 9,560 35 10751 11100 10,946 329.5 130345 9,810 35 11144 11253 11,200 337.5 130 346 10,095 45 11384 11904 11,658 342 137085 10,065 40 11342 11760 11,574 348 130347 10,255 45 11823 12187 12,001 357 130348 10,445 40 12180 12412 12,381 367 130349 10,520 40 12339 12697 12,508 *378 10,765 60 12699 12872 12,810 386.5 130350 10,970 40 12848 12973 12,904 389.5 137089 11,170 50 12949 13183 13,073 397.5 130351 11,450 40 13223 13393 13,301 407 130352 11,680 40 13408 13663 13,531 418.5 130354 12,110 40 13833 14075 13,962 427.5 130355 12,185 40 13919 14162 14,044 *435 12,505 60 14235 14970 14,629 441 130357 12,380 45 14113 14738 14,366 455 130359 12,395 40 14136 14755 14,391 466 130360 12,575 40 14571 15080 14,810 475 130362 12,400 40 14142 14764 14,400 485 137091 12,695 60 14883 15399 15,109 495 137092 12,740 50 14789 15276 15,0 46 505 137093 12,925 60 15000 15567 15,262 515 137094 13,205 80 15264 16050 15,638 525 137098 13,400 45 15568 16316 15,920 535 137099 13,455 50 15635 16395 15,991 545 137100 13,755 60 16025 16782 16,385 554 137101 13,755 70 16015 16792 16,385 564 13 7102 13,905 60 16186 16949 16,568 *565 14,065 60 16356 17127 16,765 574 137103 14,075 70 16351 17151 16,776 595 137104 14,465 100 16891 17884 17,402 604 137105 14,735 70 17324 18136 17,873 614 137106 15,055 80 18063 18644 18,353 a All 14 C dates hav e an assumed constant 405 yr reservoir age correction applied and are given in years before present. *All dates were analyzed at Lawrence Livermore National Laboratory in Livermore, California, except those indicated by asterisk (*), which were analyzed at the Swiss Federal Institute of Technology, ZŸrich (ETH) and published in Meckler et al., (2008).

PAGE 71

64 Appendix 1 (Continued). Table A1 3. Magnetic susceptibility data for core MD02 2550. Depth (cm) Magnetic Susceptibility (! ) 311 12.49 313 12.26 315 12.49 317 12.94 319 13.17 321 12.71 323 12.71 325 13.17 327 13.85 329 13.62 331 13.39 333 14.07 335 14.76 337 13.85 339 12.94 341 12.71 343 12.71 345 12.49 347 12.71 349 12.71 351 12. 71 353 12.94 355 12.03 357 11.35 359 11.12 361 11.58 363 11.58 365 12.03 367 12.49 369 12.71 371 12.94 373 12.94 375 13.17 377 13.39 379 13.62 381 13.17 383 13.17 385 13.62 387 12.94 389 12.71

PAGE 72

65 Appendix 1 (Continued). Table A1 3 (Continu ed) 391 12.71 393 12.94 395 10.22 397 8.63 399 7.95 401 7.26 403 6.81 405 6.36 407 5.90 409 5.68 411 5.68 413 5.68 415 6.13 417 6.36 419 6.36 421 6.36 423 5.90 425 5.90 427 6.13 429 6.13 431 6.13 433 6.13 435 5.68 437 5.68 439 5.45 441 5.45 443 5.45 445 5.68 447 5.90 449 5.68 451 5.68 461 6.58 463 6.36 465 5.90 467 5.68 469 5.45 471 5.68 473 5.90 475 6.13 477 6.13 479 6.36

PAGE 73

66 Appendix 1 (Continued). Table A1 3 (Continued) 481 6.81 483 6.81 485 6.58 487 6.58 489 6. 36 491 6.13 493 6.13 495 6.13 497 6.13 499 6.36 501 6.58 503 6.58 505 6.81 507 6.81 509 7.04 511 7.49 513 7.49 515 7.72 517 7.95 519 7.72 521 7.49 523 7.72 525 8.40 527 7.72 529 7.72 531 7.72 533 7.26 535 7.26 537 7.95 539 9.31 54 1 11.35 543 12.49 545 13.17 547 12.94 549 11.35 551 11.58 553 12.71 555 13.62 557 17.03 559 25.42 561 29.28

PAGE 74

67 Appendix 1 (Continued). Table A1 3 (Continued) 563 19.52 564 14.76 565 15.89 566 14.76 567 15.21 568 14.76 569 14.98 570 14.98 5 71 15.21 572 15.66 573 15.21 574 16.12 576 15.66 578 14.98 580 14.07 582 13.39 584 13.62 586 13.85 588 13.85 590 14.07 600 13.85 602 13.85 604 13.85 606 13.85 608 14.07 610 14.07 612 13.85 614 13.85 616 14.07 618 15.66 620 16.57

PAGE 75

68 Appendix 2: Chapter Two Figures

PAGE 76

69 Appendix 2. Table A2 1. Mg/Ca, Al/Ca and Mn/Ca pink G. ruber data from core MD02 2550 Sample Depth (cm) Mg/Ca (mmol/mol) Al/Ca (mol/mol) Mn/Ca (mol/mol) 311 4.24 276.1 4 559.33 312 4.15 12.79 443.15 312.5 4.38 30.41 525.98 313 4.62 259.76 1 560.13 313.5 4.20 14.92 554.76 314.5 4.03 33.25 925.10 315 4.15 82.83 1,123.09 315.5 3.88 19.78 759.70 316 3.84 23.23 693.53 316.5 3.97 30.15 1,077.19 317.5 4.00 11.30 698.74 318 18.43 495.34 2,097.07 318 4.33 20.36 756.94 318.5 4.19 28.24 940.10 319 3.96 9.02 833.89 319.5 4.03 42.10 1,123.79 320.5 4.48 7.86 839.36 321 4.29 14.60 838.40 321.5 4.44 10.73 825.05 322 4.05 13.62 749.94 322.5 3.84 342.95 645.27 323.5 4.3 3 19.58 565.46 323.5 8.56 Below Detection Limit Below Detection Limit 324 4.00 16.83 554.03 324.5 4.24 18.39 599.38 325 4.57 13.29 523.69 325.5 4.22 62.60 544.69 326.5 4.37 8.59 454.17 327.5 4.45 4.71 472.83 328 4.66 103.62 486.06 328.5 4.12 17.86 761.98 328 4.48 129.87 494.14 328 61.64 Below Detection Limit Below Detection Limit 329.5 4.05 25.53 735.50 330 4.13 20.67 612.25 330.5 4.30 332.79 693.31 331.5 4.19 6.55 881.09

PAGE 77

70 Appendix 2 (Continued). Table A2 1 (Continued) 333 6.32 Below Detec tion Limit 234.70 333 3.99 30.13 664.71 335 3.56 21.52 745.65 336 4.08 12.26 655.40 336.5 4.72 47.49 798.55 338 3.72 34.58 829.63 338.5 3.61 80.46 1,076.48 339 4.02 42.91 658.84 339.5 3.87 4.57 808.35 339.5 3.94 1,425.05 773.23 340.5 4.02 21.11 7 44.54 341 4.03 52.17 615.16 341.5 3.75 17.12 954.92 342 4.19 27.68 648.10 342 4.62 Below Detection Limit 493.39 342.5 4.26 16.33 580.44 343 4.06 232.49 748.70 343.5 4.32 Below Detection Limit 1,169.52 344 3.83 9.89 1,073.69 344.5 3.89 6.37 1,035.3 4 345 4.17 33.55 1,073.80 345.5 3.86 16.28 801.05 345.5 3.90 31.11 850.20 345.5 3.93 8.26 874.70 347 4.01 30.90 708.49 348.5 4.11 728.08 949.51 349.5 3.90 63.26 693.28 349.5 4.02 12.37 663.27 350 4.10 30.78 645.07 350 3.92 14.43 657.31 350.5 4.2 0 439.33 889.32 351.5 4.16 3.78 603.56 352 4.26 6.08 702.68 352.5 8.91 Below Detection Limit 15.98 352.5 4.04 211.48 802.17 353 16.43 Below Detection Limit 688.83 353 4.57 26.65 890.20 353 4.44 45.18 897.02 353 3.62 16.06 235.62 353.5 4.17 55.18 7 99.31 353.5 4.40 33.37 1,029.33

PAGE 78

71 Appendix 2 (Continued). Table A2 1 (Continued) 355 4.05 9.05 1,248.33 355.5 3.97 13.63 1,006.52 355.5 6.59 139.80 1,024.38 355.5 4.01 366.43 1,053.98 356.5 3.74 112.84 1,064.91 357.5 4.11 19.16 794.69 358 4.28 5,739 .40 601.88 358 4.25 28.74 522.90 358 4.06 18.30 582.08 358.5 3.97 103.46 994.23 359.5 4.03 4.61 914.80 359.5 3.81 20.63 851.37 360.5 3.99 237.89 1,115.62 361 3.92 24.07 758.14 361.5 4.02 547.04 1,010.00 362 3.53 14.87 849.90 362.5 4.57 27.36 1,06 8.32 363.5 3.69 11.34 862.80 364.5 3.75 391.04 3,084.21 365 3.48 92.88 928.15 365.5 3.84 19.67 864.11 366.5 3.72 10.39 852.50 367.5 3.73 57.90 1,125.80 368 3.59 21.27 984.92 368.5 3.56 31.28 1,337.18 369.5 3.61 12.87 1,128.71 370.5 3.84 Below Det ection Limit 922.87 370.5 3.80 9.49 895.57 371.5 4.00 496.37 989.14 372 3.65 13.84 879.27 372.5 3.52 16.10 778.46 373 3.74 65.61 1,036.72 373 9.19 Below Detection Limit 50.85 373.5 3.69 27.70 1,139.66 374.5 4.00 92.56 1,107.61 375 3.47 29.32 1,081 .70 375.5 3.78 21.10 1,132.89 376.5 3.66 10.92 1,106.20 378.5 3.93 124.82 618.28 379 3.59 8.31 614.34 379.5 3.71 21.64 511.41

PAGE 79

72 Appendix 2 (Continued). Table A2 1 (Continued) 380.5 3.77 23.02 748.28 381 3.64 27.27 1,455.89 384 3.97 77.59 1,468.22 3 85 3.92 38.77 1,121.33 385 4.67 Below Detection Limit 1,019.92 385 5.39 Below Detection Limit 605.46 385.5 3.69 135.29 1,615.27 386 4.60 16.92 1,189.87 387.5 3.92 26.75 1,063.82 388 3.89 37.31 1,384.73 388.5 4.13 25.63 1,104.65 389.5 3.90 15.27 1,1 06.14 390 3.78 17.53 579.64 390.5 4.04 19.60 950.55 391.5 3.74 35.43 615.56 392 4.12 25.93 388.13 392.5 3.94 22.07 691.54 393 4.08 22.11 539.31 393.5 3.76 37.68 222.11 394 3.95 52.06 266.80 395.5 4.00 32.08 212.76 396.5 3.86 18.60 217.57 397 3.7 5 13.18 263.28 397.5 3.94 30.35 177.12 399 3.93 11.19 209.58 399.5 4.02 27.39 192.34 400 3.98 18.29 191.30 400.5 3.69 8.95 212.33 401 3.57 Below Detection Limit 188.77 401.5 3.66 24.75 158.44 402 3.46 19.91 205.81 402.5 3.60 9.30 193.88 403 4.01 50.80 209.45 403.5 3.65 13.26 203.15 405 3.90 10.44 149.75 405.5 4.13 43.96 184.64 406.5 4.30 15.16 156.51 407 3.78 21.11 184.21 407.5 4.13 34.08 164.46 408 4.14 24.26 199.56 408.5 3.71 12.08 125.54

PAGE 80

73 Appendix 2 (Continued). Table A2 1 (Continued) 409 3.75 30.29 183.31 409.5 3.86 27.17 201.80 410 3.62 10.79 178.08 410.5 3.94 37.64 183.79 411 4.45 19.54 168.55 411.5 4.17 22.01 183.57 412 4.05 258.78 269.42 412.5 4.14 14.88 140.41 413 4.06 25.18 172.80 413 4.10 14.38 171.84 413.5 3.53 14.77 141.43 414 3.64 Below Detection Limit 165.64 414.5 3.97 18.86 167.00 415 6.13 1.65 238.54 415 4.35 93.80 236.36 415.5 3.69 52.14 310.92 415.5 20.81 806.27 2,150.87 416 3.76 22.30 229.97 416.5 3.93 12.92 176.71 417 3.87 20.13 192.41 417.5 3.86 14. 95 183.29 418 3.78 15.11 163.80 418.5 3.84 25.81 220.72 419 3.85 13.96 180.13 419.5 3.95 49.83 256.24 420 9.26 Below Detection Limit 37.12 420 3.79 39.52 225.23 420.5 3.79 17.74 160.34 421 3.62 17.56 194.44 421 3.54 9.70 184.39 421.5 20.46 691.44 2,199.97 421.5 3.81 111.65 212.10 422 3.61 8.29 255.68 422.5 3.46 41.82 210.97 423 3.58 15.39 182.22 423.5 3.47 14.01 161.47 424 3.79 6.45 203.23 424.5 4.05 19.84 212.12 425 3.89 11.44 185.60 425.5 3.60 10.55 168.53 426 3.49 49.69 181.76

PAGE 81

74 Append ix 2 (Continued). Table A2 1 (Continued) 426.5 12.86 224.29 346.84 427 3.37 9.50 211.75 427.5 3.51 84.36 247.51 428 3.60 40.03 209.67 428.5 3.61 35.45 277.74 429 3.41 36.81 262.86 429.5 3.67 75.93 308.68 430 3.44 12.92 227.60 430.5 3.76 85.65 333. 12 431 3.35 28.57 188.35 431.5 6.34 855.83 212.11 431.5 14.72 384.71 463.76 432 3.48 60.07 274.81 432.5 3.61 90.35 323.68 433 3.82 11.54 281.01 433.5 3.86 17.04 240.44 434 4.12 560.90 454.11 434.5 3.90 20.41 340.57 435 3.73 23.81 421.41 435.5 3. 86 113.51 401.36 435.5 9.67 Below Detection Limit 57.55 438 3.74 14.78 365.76 438.5 3.47 42.80 350.88 439 3.77 49.60 308.58 439.5 3.90 18.96 373.23 441.5 4.08 11.77 355.81 454.5 4.05 28.50 198.30 457.5 3.76 26.76 179.17 458 4.08 99.24 218.63 458. 5 4.15 447.03 257.55 459 4.25 15.63 226.45 459.5 4.38 22.60 275.78 460 4.27 21.66 204.06 460.5 4.93 Below Detection Limit 131.87 460.5 3.87 48.05 168.73 461 4.27 16.06 169.98 461.5 3.98 10.38 192.12 462 4.08 16.15 205.47 462.5 3.77 19.54 201.24 4 63 3.82 34.24 277.55 463.5 3.76 23.05 204.77

PAGE 82

75 Appendix 2 (Continued). Table A2 1 (Continued) 464 3.58 15.47 191.29 464.5 4.26 62.92 222.71 465.5 4.15 23.76 251.83 465 3.89 21.95 181.69 466 3.93 Below Detection Limit 191.70 467 4.23 Below Detection L imit 219.73 467 4.04 297.31 177.04 468 4.51 Below Detection Limit 173.62 469 3.85 16.43 225.93 470 3.93 41.54 143.09 471 3.74 Below Detection Limit 168.19 471 3.68 12.29 198.77 472 3.89 2.06 173.23 473 4.13 1.75 211.50 474 3.94 Below Detection Lim it 151.33 475 4.15 Below Detection Limit 173.40 475 3.81 22.83 166.01 475 3.98 12.26 207.09 476 4.10 74.14 187.37 477 4.37 13.28 141.99 477 4.06 16.19 231.99 477 3.91 2.27 163.90 478 3.83 9.23 181.26 478 3.99 66.59 230.69 479 3.95 Below Detection Limit 178.74 480 3.89 59.50 150.14 480 4.02 57.62 121.34 480 3.91 7.02 149.26 480 4.64 Below Detection Limit 117.44 480 4.07 44.12 161.79 481 3.65 20.82 128.55 482 3.72 Below Detection Limit 143.61 482 3.92 3.53 184.41 483 4.15 39.44 187.76 483 19.65 400.20 2,376.98 483 3.92 15.81 212.96 483 4.13 61.64 192.77 484 3.61 3.66 182.65 484 4.03 11.85 191.79 485 3.82 7.08 166.87 485 3.83 16.02 146.72

PAGE 83

76 Appendix 2 (Continued). Table A2 1 (Continued) 486 3.85 24.62 166.07 487 3.69 Below Detection L imit 143.73 487 3.77 8.45 141.79 488 3.77 7.47 198.98 489 3.85 Below Detection Limit 180.62 489 3.89 10.00 220.70 490 3.99 11.69 165.16 491 3.51 13.64 148.13 491 3.56 25.16 139.16 492 3.69 Below Detection Limit 165.21 492 3.66 229.17 180.61 493 4 .01 33.77 182.20 494 3.68 128.07 120.54 494 3.86 20.58 147.10 494 19.81 412.43 2,384.50 494 4.02 118.18 143.27 495 3.78 5.97 214.85 496 3.81 19.69 148.71 497 3.64 Below Detection Limit 194.99 497 3.89 Below Detection Limit 164.87 498 17.39 361.61 2,070.07 498 3.93 150.99 291.64 499 3.99 Below Detection Limit 151.19 499 4.02 2.28 187.61 500 3.90 6.24 144.27 501 3.91 Below Detection Limit 162.52 501 3.93 25.97 172.67 502 5.11 Below Detection Limit 115.77 502 4.20 Below Detection Limit 149.71 502 4.02 43.34 163.77 502 4.08 44.45 162.15 503 3.76 Below Detection Limit 169.68 504 3.67 161.33 123.80 505 3.86 Below Detection Limit 187.80 505 3.91 Below Detection Limit 174.86 506 3.88 919.04 167.41 507 3.44 Below Detection Limit 168.15 507 3 .68 3.10 177.30 508 4.33 8.45 182.89 510 3.89 12.86 173.28 511 4.00 512.14 182.16

PAGE 84

77 Appendix 2 (Continued). Table A2 1 (Continued) 512 3.84 Below Detection Limit 169.01 512 3.94 16.55 169.54 514 3.88 25.14 180.22 514 3.74 11.48 182.32 516 3.89 35.05 177.16 517 3.76 9.75 175.08 518 3.73 13.90 183.70 519 4.19 Below Detection Limit 174.36 519 3.76 7.61 170.73 520 3.84 10.42 163.69 522 4.20 13.97 167.60 522 4.34 Below Detection Limit 183.09 524 4.38 107.11 195.78 524 4.36 123.36 206.70 525 3.45 11.79 158.12 526 3.56 Below Detection Limit 169.96 526 3.68 183.65 188.31 527 3.56 17.43 174.38 527 3.58 Below Detection Limit 184.49 528 3.78 795.00 188.27 528 4.00 Below Detection Limit 195.82 529 3.92 Below Detection Limit 191.06 529 4.15 15.94 220.86 530 3.81 2,415.03 215.98 531 3.72 16.83 206.89 532 3.78 12.11 238.35 533 3.66 120.56 231.64 534 3.66 510.35 229.95 534 3.74 128.67 274.53 535 3.60 Below Detection Limit 210.68 536 3.74 2,721.48 256.51 538 3.84 4.76 317.45 539 3.80 13.69 2 43.38 540 3.33 3.73 452.29 541 3.87 158.55 248.76 542 3.94 10.12 322.02 543 3.31 9.16 798.86 544 10.07 Below Detection Limit 77.85 545 3.33 6.62 849.84 547 3.72 44.50 401.01 548 3.63 28.72 360.36

PAGE 85

78 Appendix 2 (Continued). Table A2 1 (Continued) 549 3.54 38.53 297.17 550 3.70 10.34 185.72 551 3.98 52.09 291.66 554 4.16 46.08 390.82 555 3.94 22.82 340.56 557 4.04 180.62 403.96 558 3.56 41.12 433.86 559 3.48 376.22 422.79 560 3.69 67.96 514.30 562 3.39 54.86 609.40 563 3.52 48.20 677.30 565 3.60 142.15 869.45 570 3.27 95.36 1,149.61 571 3.21 32.86 1,160.93 572 3.30 81.66 1,111.40 573 3.06 101.94 1,108.71 575 3.23 79.42 1,048.71 577 3.39 72.38 959.68 578 3.23 29.75 791.25 579 3.76 6.31 752.13 580 3.19 49.33 811.08 581 16.60 169.70 51 2.33 582 3.39 754.62 1,001.48 583 3.20 63.43 1,117.46 585 3.27 41.65 1,147.88 589 3.17 132.00 869.60 590 3.04 103.78 790.02 592 3.49 52.02 644.30 593 3.50 7.58 691.28 593 3.48 89.26 674.42 597 3.00 52.38 1,089.35 598 3.19 16.28 1,055.64 598 3.02 Below Detection Limit 998.25 599 3.31 162.39 999.08 599 3.09 4.70 969.07 600 2.99 10.44 776.45 601 2.74 Below Detection Limit 875.29 601 2.61 181.15 866.22 602 2.96 34.96 835.11 603 3.16 20.63 819.13 607 3.04 90.96 793.66

PAGE 86

79 Appendix 2 (Continued). Table A2 1 (Continued) 610 3.17 50.61 951.19 611 3.21 31.76 933.62 612 2.98 49.69 935.60 612 3.12 Below Detection Limit 1,081.53 613 3.49 33.90 1,011.65 617 3.18 34.93 706.21 618 3.36 37.27 767.18 618 3.37 Below Detection Limit 741.91 619 3.28 Bel ow Detection Limit 656.25 619 3.48 32.49 708.00 620 3.35 86.33 883.23 621 3.38 29.01 838.31 a Al/Ca ratios in red indicate value exceeds 200 mol/mol threshold; corresponding Mg/Ca measurements have been removed from data set analysis. White G. ruber data is reported in Williams et al., (2008).

PAGE 87

80 Appendix 2 (Continued). 2.5 3 3.5 4 4.5 5 Mg/Ca (mmol/mol) -50 0 50 100 150 200 Al/Ca (ummol/mol) 0 500 1,000 1,500 2,000 300 350 400 450 500 550 600 650 Mn/Ca (ummol/mol) Depth (cm) a b c Figure A2 1: Raw pink G. ruber data vs. depth from Core MD02 2550. (a) Mg/Ca data. Average precision is 0.01 mmol/mol. (b) Al/Ca data are used to monit or clay removal. No correlation is seen between Al/Ca and Mg/Ca values (r 2 = 0.02). (b) Mn/Ca data, used to monitor Mn Fe oxides. No correlation is seen between Mn/Ca and Mg/Ca values (r 2 = 0.01).

PAGE 88

81 Appendix 2 (Continued). 10,000 12,000 14,000 16,000 18,000 20,000 300 350 400 450 500 550 600 650 Calendar Yrs B.P. Depth (cm) Y=(3.205 x 10 4 )x 3 0.4545x 2 + 232.5x (2.738 x 10 4 ) Figure A2 2: Age model fo r core MD02 2550, based on 34 radiocarbon dates, from monospecific planktonic Foraminifera ( G. ruber ). Error bars represent 2 sigma error in calibration from radiocarbon to calendar years. All 14 C dates were calibrated to calendar years using the MARINE0 4 calibration data set [ Hughen et al. 2004] and have an assumed constant 405 yrs r eservoir correction applied.


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Meltwater and abrupt climate change during the last deglaciation :
b a Gulf of Mexico perspective
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by Clare C. Williams.
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[Tampa, Fla] :
University of South Florida,
2009.
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Thesis (M.S.)--University of South Florida, 2009.
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Text (Electronic thesis) in PDF format.
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Advisor: Benjamin P. Flower, Ph.D.
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ABSTRACT: During the last deglaciation, Greenland ice core records exhibit multiple, high frequency climate events including the Oldest Dryas, Blling-Allerd and Younger Dryas, which may be linked to meltwater routing of the Laurentide Ice Sheet (LIS). Previous studies show episodic meltwater input, via the Mississippi River to the Gulf of Mexico (GOM) several thousand years before the onset of the Younger Dryas until ~13.0 kcal (thousand calendar) yrs, when meltwater may have switched to an eastern spillway, reducing thermohaline circulation (THC). Data from laminated Orca Basin in the GOM, constrained by 34 Accelerator Mass Spectrometry (AMS) C dates, provide the necessary resolution to assess GOM sea-surface temperature (SST) history and test the meltwater routing hypothesis.Paired Mg/Ca and O data on the Foraminifera species Globigerinoides ruber (pink and white varieties) document the timing of meltwater input and temperature change with decadal resolution. White G. ruber SST results show an early 5C increase at 17.6-16.0 kcal yrs and several SST decreases, including at 16.0-14.7 kcal yrs during the Oldest Dryas (2C) and at 12.9-11.7 kcal yrs during the Younger Dryas (2.5C). While the early deglaciation shows strong similarities to records from Antarctica and Tobago Basin, the late deglaciation displays climate events that coincide with Greenland and Cariaco Basin records, suggesting that GOM SST is linked to both northern and southern hemisphere climate. Isolation of the ice-volume corrected O composition of seawater (O[subscript GOM]) shows multiple episodes of meltwater at ~16.4-15.7 kcal yrs and ~15.2-13.1 kcal yrs with white G. ruber O[subscript GOM] values as low as -2.5%.The raw radiocarbon age of the cessation of meltwater in the GOM (11.3750.40 C kcal yrs) is synchronous with large changes in tropical surface water C, a proxy for THC strength. An early meltwater episode beginning at 16.4 kcal yrs during the Oldest Dryas supports the suggestion of enhanced seasonality in the northern North Atlantic during Greenland stadials. We suggest a corollary to the seasonality hypothesis that in addition to extreme winters during stadials, warm summers allowed for LIS melting, which may have enhanced THC slowdown.
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Paleoclimate
Younger Dryas
Oldest Dryas
Atlantic Warm Pool
Seasonality
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Masters.
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