David Hastings

The microbial ecology of oligotrophic deep ocean sediments is understudied relative to their shallow counterparts, and this lack of understanding hampers our ability to predict responses to current and future perturbations. The Gulf of Mexico has experienced two of the largest accidental marine oil spills, the 1979 Ixtoc-1 blowout and the 2010 Deepwater Horizon (DWH) discharge. Here, microbial communities were characterized for 29 sites across multiple years in >700 samples. The composition of the seafloor microbiome was broadly consistent across the region and was well approximated by the overlying water depth and depth within the sediment column, while geographic distance played a limited role. Biogeographical distributions were employed to generate predictive models for over 4000 OTU that leverage easy-to-obtain geospatial variables which are linked to measured sedimentary oxygen profiles. Depth stratification and putative niche diversification are evidenced by the distributio...

Following the Deepwater Horizon (DWH) event in 2010 subsurface hydrocarbon intrusions (1000-1300 m) and an order of magnitude increase in flocculent hydrocarbon deposition caused increased concentrations of hydrocarbons in continental slope sediments. This study sought to characterize the variability [density, Fisher's alpha (S), equitability (E), Shannon (H)] of benthic foraminifera following the DWH event. A series of sediment cores were collected at two sites in the northeastern Gulf of Mexico from 2010 to 2012. At each site, three cores were utilized for benthic faunal analysis, organic geochemistry, and redox metal chemistry, respectively. The surface intervals (∼0-10 mm) of the sedimentary records collected in December 2010 at DSH08 and February 2011 at PCB06 were characterized by significant decreases in foraminiferal density, S, E, and H, relative to the down-core intervals as well as previous surveys. Non-metric multidimensional scaling (nMDS) analysis suggested that a ...

Oxygen isotope data from the Pleistocene section of Ocean Drilling Program (ODP) Site 1130 in the Great Australian Bight (GBA) show that shelf sediment export along the cool-water carbonate margin is linked to changes in global ice volume. The GAB is a site of extensive cool-water carbonate deposition, but little is known about how these deposits respond to climatic fluctuations. Overall, these rapidly deposited sediments exhibit a shallowing upward sequence, which is likely due to the progradation of the shelf margin during the Pleistocene. Superimposed on this, is a meter scale cyclic alternation between dark-colored, coarser-grained, high-Mg calcite units and light-colored, fine-grained, carbonate-rich units consisting predominantly of low-Mg calcite. The former was interpreted to represent enhanced shelf sediment export. The latter was interpreted to represent a strong pelagic contribution due to a decrease in shelf sediment export. Oxygen isotope analyses using Gs. ruber, condu...

Following the blowout of the Macondo well, a pulse in sedimentation resulted in changes in sedimentary redox conditions. This is demonstrated by downcore and temporal changes in the concentration of redox sensitive metals: Mn, Re, and Cd. Sediment cores collected in the NE Gulf of Mexico (GoM) reveal increased sedimentation after the Deepwater Horizon (DWH) blowout. The formation of mucous-rich marine snow in surface waters and subsequent rapid deposition to underlying sediments is the likely cause. Respiration of this material resulted in decreased pore-water oxygen concentration and a shoaled redoxcline, resulting in two distinct Mn peaks in sediments following the event, one typically in the top 10 mm, with the other at 20–30 mm. Most cores near the wellhead reveal this non-steady state behavior for up to two years after the event. Associated with the Mn minimum between the two Mn peaks, a modest (15–30%) enrichment of Re consistent with reducing sediments typically exists. A three-year time series of three stations following the event reveal that sediment Re increased 3–4 times compared to the pre-impact baseline value for two years, indicating sediments are increasingly more reducing for two years. In the third year, Re concentration decreased, suggesting a return towards pre-impact conditions. In select sites where the density of benthic foraminifera was determined, an assemblage-wide decrease occurred coincident with reducing conditions as determined by redox sensitive metals, demonstrating the important consequences of changing redox conditions on benthic ecosystems. Determination of redox sensitive metals will continue to constrain the temporal evolution of reducing conditions, which will serve to document the long-term effects of the spill, and the possible return to pre-event conditions.

Abstract—We have determined the chlorophyll pigment composition by liquid chromatography (LC) and LC/MS/MS in a 1.45-m long freeze core, representing 157 years of annually varved sedimentation, from Saanich Inlet, B.C, Canada. We investigated the very early diagenetic processes of chlorophyll a alteration in these anoxic sediments and the possible implications for palaeoproductivity studies. Excellent preservation of pigments is indicated by high total pigment concentrations, and the presence of labile compounds such as chlorophyllide a. The lack of systematic down core changes in both the total pigment concentration and the chlorin composition indicates that no detectable alteration of the pigment composition has occurred during the past 157 years. The sedimentary pigment composition is the result of processes occurring in the water column, or within few months after deposition. Chlorophyll derivatives corresponding to different diagenetic processes have distinct down core profiles...

Copyright: © 2015 Schwing et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Table 1. Short-lived radioisotope (210Pb, 234Th) activities, constant rate of supply agemodel, total organic carbon (TOC) percentages and TOC ac-cumulation rates with depth for each core [29]. Depth Excess 210Pb 210Pb Error Total 234Th 234Th Error CRS Date CRS Error TOC TOC Acc. Rate

Abstract-We assess the potential of using foraminiferal calcite as a paleoceanographic indicator of seawater V concentrations. Laboratory culture experiments show that living benthic and planktonic foraminifera incorporate V into their test in direct proportion to seawater concentrations. Distribution coefficients relative to the culture solution are D = 2.1 X 10m3 and 2.8 X 10m3 for G. calida and A. lobifera, respectively. We use a cleaning procedure that effectively removes most V-rich contaminant phases from foraminiferal calcite preserved in the fossil record including organic matter and Mn-Fe oxyhydroxides. MnC03 overgrowths cannot be eliminated. Since V is conservative in the ocean, forami-niferal calcite recently accreted and found in surface sediment samples should have the same V content if this tracer accurately reflects seawater concentrations. V/Ca values for the same species of foraminifera are constant for core-top samples collected above the foraminiferal lysocline in...

One of the most critical tools for understanding the forcing of climate change is establishing the relative timing of changes in climate-related parameters such as sea-surface temperature, ice volume, salinity, and atmospheric carbon dioxide. Recently, the use of multiple geochemical proxies in foraminifers has emerged as a powerful technique for identifying changes in sea-surface temperature, ice volume, and salinity. Since these measurements are all based on the same sample, this approach improves the accuracy of leads and lags in timing by avoiding errors inherent in matching different age models (for example, for ice versus marine sediment cores) as well as ambiguities inherent in combining data from different sources (ie alkenone-based SST and foraminiferal δO). Here we use combined measurements of U/Ca and Mg/Ca in G. ruber from a Caribbean core (ODP999A) to examine the relative timing of changes in SST and atmospheric pCO2 at the end of the last glacial maximum and early degl...

As part of the Western Hemisphere Warm Pool (WHWP), the Gulf of Mexico (GOM) is an important part of the tropical heat engine and a major source of heat and moisture to the North American continent and the higher latitudes. Laminated Orca Basin on the Louisiana slope in the northern GOM provides a unique, high-resolution record of WHWP sea-surface temperature

The Gulf of Mexico (GOM) is part of the Western Hemisphere Warm Pool providing a source of heat and moisture to the North American continent and Northern high latitudes. Paleoclimatic records from the GOM can test the hypothesis that the tropical climate system is an important driver of past global climate change. In July 2002, core MD02-2551 was taken by

Routing of low-salinity meltwater from the Laurentide Ice Sheet (LIS) into the North Atlantic via eastern outlets (e.g., St. Lawrence and Hudson River systems) and northern outlets (e.g., Hudson Bay and Arctic Ocean) is thought to have reduced Atlantic meridional overturning circulation (AMOC) and thereby triggered rapid regional to global climate change during the last glacial cycle. In contrast, southward

ABSTRACT During Late Pleistocene glacial terminations Laurentide Ice Sheet (LIS) meltwater enters the Gulf of Mexico (GOM). As of yet, it is unclear whether or not weak warm periods, such as marine isotope stages (MIS) 3, 5a and 5c, were associated with meltwater discharge events. It is equally unknown how the timing of these events, if they existed, relates to millennial scale warm intervals determined from Greenland and Antarctic ice core records. To understand the dynamics of LIS melting we investigate the phasing between meltwater events and sea surface temperature (SST) changes. ODP site 625, drilled at a water depth of ~900 m near De Soto Canyon, provide continuous records of MIS 2-6 sampled at a mean temporal resolution of ~400 years. Results from paired Mg/Ca-SST and delta18O on Globigerinoides ruber (white and pink variety) provide evidence for orbital-to millennial influence on salinity and temperature in the GOM. Across the MIS 6/5 termination SST increases ~1000 years before changes in delta18O seawater, a result similar to the most recent deglaciation. Considering that Holocene G. ruber (pink) delta18O values are -1.50/00, MIS 3 and 5 exhibit negative excursions of 0.50/00 or more with values reaching -2.80/00. The greater than 10/00 excursions, which cannot be attributed solely to temperature, suggest significant salinity changes. The timing of southern routing of LIS meltwater has implications for potential disruption of meridional overturning circulation (MOC) during late Pleistocene orbital- to millennial-scale climate changes. However, the initial forcing to instigate large meltwater perturbations is ambiguous. Determining the phasing of regional SST and LIS meltwater events in relationship to high latitude records will increase understanding of important climate feedbacks and the role of the tropics in climate change.

An 11.28 m core collected in Tampa Bay, FL reveals lacustrine sediments during the deglacial warming. Mg/Ca, Sr/Ca and O-18 were measured on two species of brackish water ostracodes. Our interpretation is that variations in Sr/Ca reflect changes in water chemistry and Mg/Ca variations reflect changes in both water temperature and chemistry. Applying Sr distribution coefficients results in virtually identical

Following the blowout of the Macondo well, a sedimentation pulse resulted in significant changes in sedimentary redox conditions. This is demonstrated by downcore and temporal changes in the concentration of redox-sensitive metals: Mn and Re. Sediment cores collected in the NE Gulf of Mexico reveal increased sedimentation after the Deepwater Horizon (DWH) blowout. The formation of mucous-rich marine snow in surface waters and subsequent rapid deposition to sediments is the likely cause. Respiration of this material resulted in decreased pore-water oxygen and a shoaled redoxcline, resulting in two distinct Mn peaks in sediments following the event, one typically in the top 5–7 mm, with the other at 20–30 mm. Cores near the wellhead reveal this nonsteady-state behavior for 3–5 years after the event. A time series reveals that bulk sediment Re increased 3–4 times compared to the pre-impact baseline value for 2–3 years indicating sediments are increasingly more reducing. Three years aft...

Marine Oil Snow Sedimentation and Flocculent Accumulation (MOSSFA) refers to the process of formation, sinking, and seafloor deposition of oil-contaminated marine snow and oil-mineral aggregates. MOSSFA was well documented in the northern Gulf of Mexico (GoM) in the aftermath of the Deepwater Horizon (DWH 2010) and likely occurred in the southern GoM during Ixtoc 1 (1979–1980). This chapter introduces Part IV: Oil Spill Records in Deep Sea Sediments and addresses a series of questions regarding MOSSFA in the sedimentary record: What were the characteristics of MOSSFA sedimentary inputs? What was the extent of MOSSFA on the seafloor? What postdepositional processes took place as a result of MOSSFA? Can MOSSFA be preserved in the sedimentary record?

A series of recent papers has called for multiple radiocarbon dates on planktic foraminifera to assess stratigraphic continuity in deep-sea sediment cores. This recommendation comes from observations of anomalous14C dates in planktic foraminifera from the same stratigraphic level. Potential reasons include bioturbation, downslope transport, secondary calcification, carbonate dissolution, and differential preservation. In this study, paired14C dates on dissolution-susceptibleGlobigerinoides ruberand dissolution-resistantNeogloboquadrina dutertreiare used to evaluate a Gulf of Mexico sediment core. Fourteen of 15 pairs (between 8815 and 12,995 uncorrected14C yr BP) yield concordant uncorrected14C ages (mean difference −2 ± 75 yr), attesting to continuous deposition at high accumulation rates…

ABSTRACT During Late Pleistocene glacial terminations Laurentide Ice Sheet (LIS) meltwater enters the Gulf of Mexico (GOM). As of yet, it is unclear whether or not weak warm periods, such as marine isotope stages (MIS) 3, 5a and 5c, were associated with meltwater discharge events. It is equally unknown how the timing of these events, if they existed, relates to millennial scale warm intervals determined from Greenland and Antarctic ice core records. To understand the dynamics of LIS melting we investigate the phasing between meltwater events and sea surface temperature (SST) changes. ODP site 625, drilled at a water depth of ~900 m near De Soto Canyon, provide continuous records of MIS 2-6 sampled at a mean temporal resolution of ~400 years. Results from paired Mg/Ca-SST and delta18O on Globigerinoides ruber (white and pink variety) provide evidence for orbital-to millennial influence on salinity and temperature in the GOM. Across the MIS 6/5 termination SST increases ~1000 years before changes in delta18O seawater, a result similar to the most recent deglaciation. Considering that Holocene G. ruber (pink) delta18O values are -1.50/00, MIS 3 and 5 exhibit negative excursions of 0.50/00 or more with values reaching -2.80/00. The greater than 10/00 excursions, which cannot be attributed solely to temperature, suggest significant salinity changes. The timing of southern routing of LIS meltwater has implications for potential disruption of meridional overturning circulation (MOC) during late Pleistocene orbital- to millennial-scale climate changes. However, the initial forcing to instigate large meltwater perturbations is ambiguous. Determining the phasing of regional SST and LIS meltwater events in relationship to high latitude records will increase understanding of important climate feedbacks and the role of the tropics in climate change.

Evidence is emerging that the tropical climate system played a major role in past global climate change during the last glacial cycle. However, existing studies indicate asynchronous temperature variability in the western equatorial Atlantic, complicating the identification of causal mechanisms. Because the Gulf of Mexico (GOM) is linked to the equatorial Atlantic, sea-surface temperature (SST) records from the GOM help assess the phasing between low- and high-latitude Atlantic climate. High sedimentation rates of >40 cm/k.y. and laminated sediments in Orca Basin allow sub-centennial-scale resolution. Paired delta 18O and Mg/Ca data on the planktic foraminifer Globigerinoides ruber from core EN32-PC6 are used to separate deglacial changes in SST and delta 18Oseawater due to low-salinity meltwater from the Laurentide Ice Sheet (LIS). Mg-SST increases by >3.0° C between 17.2 and 15.2 ka (calendar years) encompassing Heinrich Event 1 in the North Atlantic. Comparison to polar ice...

Reconstruction of past sea surface temperatures (SST) is essential for understanding processes that have controlled climate change throughout Earth's history. The amplitude of tropical SST estimates using different proxies varies substantially, limiting our ability to constrain the role of ocean heat transport in climate change. Mg/Ca ratios in planktonic foraminifera are a relatively recent tool assessing SST. Before this new tool can be fully exploited it is necessary to compare foraminiferal Mg estimates with methods that are more fully established. We sampled an AMS 14C-dated core (SONNE-115 GC 18287-3; 5° 39.781'N; 110° 39.689'E) from 598 m water depth in the Southern South China Sea that spans the late glacial to Holocene transition. This site is from a non-upwelling environment within the Western Pacific Warm Pool. We present a high-resolution record of three independent paleotemperature assessments: Mg/Ca ratios from planktonic foraminifera (G. ruber and G. saccu...

The objective of this study is to reconstruct the climate history of Tampa Bay, Florida over the Holocene epoch using the benthic foraminifera Ammonia beccarii from five sediment cores. Here we present a reconstruction based on oxygen isotopic ratios and Mg/Ca data that provides critical information on the history of climate changes in southwest Florida. Oxygen isotopes and Mg/Ca data from samples of A. beccarii taken from a series of five sediment cores provide records of temperature and salinity changes in Tampa Bay over the last 10,000 years. Sample age was constrained using a total of 21 AMS radiocarbon dates, 11 measured on A. beccarii and 10 measured on other material in the sediment (shell, bulk organic sediment, mollusk, organic sediment, and plant). The temperature reconstruction we present provides evidence of significant variability in the climate of Tampa Bay throughout the Holocene epoch, as indicated by a relative temperature range of 6° C. The highest reconstructed te...

ABSTRACT During Late Pleistocene glacial terminations Laurentide Ice Sheet (LIS) meltwater enters the Gulf of Mexico (GOM). As of yet, it is unclear whether or not weak warm periods, such as marine isotope stages (MIS) 3, 5a and 5c, were associated with meltwater discharge events. It is equally unknown how the timing of these events, if they existed, relates to millennial scale warm intervals determined from Greenland and Antarctic ice core records. To understand the dynamics of LIS melting we investigate the phasing between meltwater events and sea surface temperature (SST) changes. ODP site 625, drilled at a water depth of ~900 m near De Soto Canyon, provide continuous records of MIS 2-6 sampled at a mean temporal resolution of ~400 years. Results from paired Mg/Ca-SST and delta18O on Globigerinoides ruber (white and pink variety) provide evidence for orbital-to millennial influence on salinity and temperature in the GOM. Across the MIS 6/5 termination SST increases ~1000 years before changes in delta18O seawater, a result similar to the most recent deglaciation. Considering that Holocene G. ruber (pink) delta18O values are -1.50/00, MIS 3 and 5 exhibit negative excursions of 0.50/00 or more with values reaching -2.80/00. The greater than 10/00 excursions, which cannot be attributed solely to temperature, suggest significant salinity changes. The timing of southern routing of LIS meltwater has implications for potential disruption of meridional overturning circulation (MOC) during late Pleistocene orbital- to millennial-scale climate changes. However, the initial forcing to instigate large meltwater perturbations is ambiguous. Determining the phasing of regional SST and LIS meltwater events in relationship to high latitude records will increase understanding of important climate feedbacks and the role of the tropics in climate change.

An 11.28 m core collected in Tampa Bay, FL reveals lacustrine sediments during the deglacial warming. Mg/Ca, Sr/Ca and O-18 were measured on two species of brackish water ostracodes. Our interpretation is that variations in Sr/Ca reflect changes in water chemistry and Mg/Ca variations reflect changes in both water temperature and chemistry. Applying Sr distribution coefficients results in virtually identical

The Gulf of Mexico (GOM) is part of the Western Hemisphere Warm Pool providing a source of heat and moisture to the North American continent and Northern high latitudes. Paleoclimatic records from the GOM can test the hypothesis that the tropical climate system is an important driver of past global climate change. In July 2002, core MD02-2551 was taken by

Global climate change is widely recognized as the most important environmental problem today that requires complex, global solutions with international cooperation. Teaching the science of climate change is relatively simple compared to the challenges of determining solutions to this problem. It is important for students to learn that solutions do exist and that international negotiations are underway to achieve reductions.

ABSTRACT We developed a method to measure picogram quantities of vanadium in calcite and seawater by isotope dilution (ID) inductively coupled plasma mass spectrometry using electrothermal vaporization (ETV) to introduce the sample into the plasma. A 50V isotope spike enriched to 44 atom % was equilibrated with samples, followed by chemical purification by cation exchange chromatography. Samples were introduced into the ETV unit with a Pd modifier and heated to 1000 °C. This quantitatively eliminates the ClO+ isobaric interference with V at m/z 51 for solutions up to 0.5 N HCl. The procedural blank was 0.27 pg of V. Corrections for 50Ti and 50Cr, which interfere with the 50V signal, were made by measurement of 49Ti and 53Cr. These isobaric interferences and variable ArC levels were the limiting sources of error in the ID measurement and diminished the detection limit to 6 pg of V. The detection limit for nonisotope dilution applications was 0.3 pg of V. Measurement precision on the same sample of dissolved calcite over the course of one run was ±3% (1σ). Accuracy was confirmed by determination of V standards in CaCO3 and by comparative measurement with ID thermal ionization mass spectrometry and graphite furnace atomic absorption spectroscopy.

ABSTRACT We report initial results to determine if select trace metals are effective indicators for the magnitude and spatial extent of Deep Water Horizon (DWH) oil contamination in Gulf of Mexico marine sediments and beach sands. Since crude oil is known to have elevated concentrations of nickel and vanadium, contamination can be detected even after the degradation of oil by measuring enrichment of these metals within marine sediments and beach sands. A sample of crude oil from the Macondo Prospect, source of the Deepwater Horizon (DWH) oil spill, was fully digested and analyzed by inductively coupled plasma mass spectrometry (ICP-MS) at the College of Marine Science, University of South Florida. Results indicate the crude oil is enriched in nickel, vanadium, and cobalt, with concentrations of 0.86 ppm, 2.76 ppm, and 84 ppb, respectively. With this known trace metal enrichment in DWH oil, Gulf of Mexico marine sediments from 400 and 1100m water depth near DeSoto Canyon and beach sands from Pensacola, FL were examined for enrichment of V, Ni, and Co. Both marine sediment and beach sand samples were partially digested with HNO3 before analysis via ICP-MS. With marine sediments, the visually contaminated layer at or near the surface typically exhibited an enrichment in Ni, V, and Co compared to the pristine control sediments. Vanadium and nickel enrichment in marine sediments varied from 10 to 32% and 0 to 22%, respectively. Visible contamination in beach sands was found between 20-60cm beneath the surface and, likewise, showed Ni, V, and Co enrichment up to 33%, 45%, and 100%. This data shows that enrichment of V, Ni, and Co in marine sediments and beach sands may be an effective proxy for contamination even after the degradation of oil. Marine sediments and beach sands will continue to be monitored for trace metal enrichment in an effort to assess the continuing impacts of the DWH spill on the Gulf of Mexico.

ABSTRACT The interactions between low-latitude Atlantic climate and high-latitude ice sheet variability represent an important issue in past abrupt climate change. Specifically, Laurentide Ice Sheet (LIS) meltwater input seems to be decoupled at the millennial scale from Gulf of Mexico sea-surface temperature (SST), as well as Greenland air temperature, during the last glacial cycle. Indeed, comparison to Greenland ice core records indicate significant meltwater input during some North Atlantic cool episodes, including Heinrich Stadials 4, 3, and 1. Here we present published and new Mg/Ca and δ18O data on the planktic foraminifer Globigerinoides ruber from northern Gulf of Mexico sediment cores that provide detailed records of SST, δ18O of seawater (δ18Osw), and inferred salinity for the 48-10 ka interval. Age control for Orca Basin cores MD02-2550 and -2551 is based on AMS 14C dates on G. ruber and documents continuous sedimentation at rates >35 cm/kyr. Significant meltwater input is inferred from δ18Osw data during Antarctic Isotope Maxima (AIM) events and reaches a peak during the Bølling/Allerød, consistent with bipolar warming and a high sensitivity to greenhouse forcing. Furthermore, bulk sediment δ18O data show a brief spike reaching -5.5% ca. 14.5 ka during an interval barren of foraminifera. We speculate that this excursion represents fine carbonate sediment from Canadian Paleozoic marine carbonates, analogous to detrital carbonate in the North Atlantic that has a δ18O value of -5%. Radiogenic isotope data (Nd and Pb) also reach peak values at this interval, indicative of older continental material sourced from Canada vs. younger material from the Mississippi River drainage basin. Inferred major meltwater flow appears to have been associated with meltwater pulse 1a within the Bølling warm interval, consistent with a significant contribution by the LIS to rapid global sea level rise. Overall, the relations between Gulf of Mexico meltwater input, Heinrich stadials, and Antarctic warm events suggest bipolar warming and enhanced seasonality during meltwater episodes, as well as a high sensitivity to atmospheric CO2 rise.

ABSTRACT Northern Gulf of Mexico (GOM) sediments document abrupt millennial-scale climate events that may be linked to significant changes in thermohaline circulation (THC) and Laurentide Ice Sheet (LIS) melting during the last deglaciation. Previous records exhibit episodic melting throughout the deglacial sequence until the Younger Dryas cold interval when meltwater input ceased ca. 12.9 ka. However, existing records lack the temporal resolution and age control to assess high-frequency changes in sea-surface temperature (SST) and LIS melting history. Here, we use a multi-proxy approach including foraminiferal (G. ruber) Ba/Ca, Mg/Ca and δ18O measurements to investigate the role of LIS meltwater in GOM climate and the relationship between melting episodes and southern ice sheet margin dynamics. High sedimentation rates (40 cm/1000 years) and 65 14C dates from core MD02-2550 from laminated Orca Basin in the northern GOM provide nearly decadal scale sampling resolution. Paired Mg/Ca-SST and δ18O data from G. ruber (white and pink varieties, separately) allow for the calculation of an ice-volume corrected δ18OSW record (termed δ18OGOM) that is strongly influenced by the highly negative δ18O value of LIS meltwater. Ba concentrations in the Mississippi River are elevated relative to the GOM and are negatively correlated to sea-surface salinity (SSS). Ba/Casw and SSS exhibit a nearly linear relationship for >20 psu, using modern data. Foraminiferal Ba/Ca exhibits a predictable relationship to Ba/Casw and may be used as a semi-quantitative tracer of SSS. δ18OGOM results reveal multiple negative excursions of >1% centered at ca. 23.4 ka, 21.2 ka, 16.6 ka, 15.1 ka and 13.4 ka, that confirm at least five melting episodes followed by a cessation of meltwater at the onset of the Younger Dryas (ca. 12.9). Preliminary Ba/Ca data exhibit large millennial-scale excursions suggesting significant Mississippi River input variability throughout the late glacial interval and deglaciation. A positive Ba/Ca excursion centered at ca. 15.0 ka indicates a low SSS event near the onset of the Bolling-Allerod, in agreement with the δ18OGOM data. Furthermore, elevated mean Ba/Ca values during the late glacial sequence (ca. 24-20 ka) suggest earlier summer melting episodes. Comparison to clay mineralogy data from nearby cores suggests the Great Lakes region may be the origin to a significant melting event (ca. 16.9-16.2 ka) followed by a northwest shift to the Mississippi and Missouri River watersheds at ca. 15.5 ka. Moreover, many melting events appear to follow significant glacial advances based on 14C-dated moraines. Meltwater input during the Mystery Interval (17.5-14.5 ka) when Greenland remained cold is consistent with mild summers and enhanced seasonality postulated for the North Atlantic region. We speculate that the LIS was highly sensitive to small changes in northern hemisphere insolation and seasonal air temperature, which may be relevant to modern mid-latitude ice sheet melting.

During the Last Glacial Termination from 18,000-8,000 cal. yrs B.P., meltwater routing of the Laurentide Ice Sheet (LIS) may have been linked to abrupt climatic events, such as the Younger Dryas. Previous studies show episodic meltwater input from the LIS, via the Mississippi River to the Gulf of Mexico (GOM) several thousand years before the onset of the Younger Dryas until approximately 13,000 cal yrs B.P., when meltwater routing may have switched to a more northern spillway, causing an abrupt change in thermohaline circulation (THC). The exact timing and magnitude of this meltwater input to the GOM is poorly constrained due to the lack of high-resolution data. Also unknown are the detailed relationships between GOM sea surface temperature, sea surface salinity and ice volume, relative to Northern and Southern Hemisphere climate from Greenland and Antarctica ice core records. High sedimentation rates (~40 cm/kyr) from laminated, anoxic Orca Basin core MD02-2550 provide the necessary resolution to assess GOM paleoceanography. Paired Mg/Ca and delta18O values from planktonic Foraminifera species Globigerinoides ruber (pink and white varieties) provide the relative timing of meltwater input and temperature change in the GOM with nearly decadal resolution. delta18Ocalcite results show multiple cool and/or high salinity periods with isotopic excursions of at least 20/00 that coincide with abrupt climatic events in Greenland ice core records, including the Oldest Dryas from 16,200-15,000 cal. yrs B.P. and the Intra-Allerod Cold Period at 13,860-13,560 cal. yrs B.P. Meltwater input to the GOM is seen for several thousand years before the onset of the Younger Dryas with white G. ruber delta18Ocalcite values as low as -40/00. Thirty-three AMS radiocarbon dates and high-resolution delta18O results provide excellent temporal constraints on deglacial climate events, including an abrupt (<200 yrs) cessation of meltwater in the GOM centered at 10,970± 40 radiocarbon yrs B.P., with a delta18O increase of 3.50/00. The delta18Ocalcite of white G. ruber shows a clearly defined Younger Dryas interval (delta18Ocalcite ~ -0.50/00) after the Cessation Event from 13,000-11,700 cal yrs B.P. Pink G. ruber displays a similar cessation of meltwater, yet exhibits a much small isotopic range (40/00 vs. 60/00 for pink and white varieties, respectively) without a fully defined Younger Dryas period. The radiocarbon age of the Cessation Event in the GOM (10,970± 40) coincides with large changes in Delta14C, a proxy for THC strength, as well as the radiocarbon onset of the Younger Dryas in European lake sediments. These results suggest that the onset of the Younger Dryas and other abrupt climate events during the Last Glacial Termination may be linked to a decrease in THC due to a change in meltwater routing of the LIS.

Sea surface temperature (SST) and delta18Osw records from the Gulf of Mexico (GOM) during the last deglaciation will help distinguish different mechanisms for abrupt climate change. Orca Basin is an ideal location to study climate changes in the GOM and to record the timing of meltwater discharge events through the Mississippi River; the anoxic hypersaline bottom water prevents bioturbation and

This study provides the first measurement of microplastic abundance and distribution in surface waters and sediments in Tampa Bay, FL. Microplastic concentrations in discrete water samples ranged from 0.25 to 7.0 particles/L with an average of 0.94 (± 0.52) particles/L. Samples taken with a 330 μm plankton net had 1.2-18.1 particles/m 3 with an average of 4.5 (± 2.3) particles/m 3. Discrete samples were 200 times higher than net samples, suggesting substantial losses or undersampling with the net. For both discrete and plankton tow samples, there were no significant differences in concentrations between stations or regions. Intense rainfall events in the summer always preceded samples with substantially higher counts. Most (> 75%) microplastics were fibers. Using an average value of 1 particle/L, Tampa Bay contains ~4 billion microplastic particles. Surface sediments had an average of 280 (± 290) particles/kg, ranging from 30 to 790 particles/kg. Highest concentrations of microplastics were found in sediments close to industrial sources; lowest values in Middle and Lower Tampa Bay are consistent with shorter residence times.