TY - JOUR T1 - Organic carbon and planktic foraminifera radiocarbon derived Holocene sediment accumulation rates in the northern slopes of the Gulf of Mexico JF - Deep Sea Research Part I: Oceanographic Research Papers Y1 - 2023 A1 - Schwing, Patrick A1 - Chanton, Jeffrey A1 - Bosman, Samantha A1 - Brooks, Gregg A1 - Larson, Rebekka A. A1 - Romero, Isabel A1 - Diercks, Arne KW - accumulation rates KW - Foraminifera KW - Gulf of Mexico KW - radiocarbon KW - Radiogeochemistry AB - In the context of climate regulation and anthropogenic waste detoxification (e.g. oil spills), estimates of deep ocean sedimentation and carbon sequestration are of the utmost importance. Radiocarbon (14C) is a common radioisotope that can be used to establish millennial scale sediment accumulation rates. The objectives of this study were to: 1) establish ages for co-occurring total organic carbon (TOC) and planktic foraminifera (carbonate) in the northeastern Gulf of Mexico (GoM), 2) use these ages to estimate accumulation rates independently, 3) identify any evidence of redistribution, and 4) examine any offset between TOC and carbonate 14C ages as a tool to potentially identify selective TOC transport. Sediment samples were collected in May 2018 from the RV Point Sur using an Ocean Instruments MC-800 multi corer. Radiocarbon measurements of both planktic foraminifera and TOC subsamples were made at the National Ocean Science Accelerator Mass Spectrometry Facility (NOSAMS). Radiocarbon ages, calibrated using the OxCal 4.4, ranged from recent to 6407 BP. Linear (LAR: 4–24 cm/kyr) and mass accumulation rates (MAR: 1.5–11.5 g/cm2/kyr) were generally consistent with those reported by other recent studies in the GoM. At two sites, C14 ages decreased from the surface to the second sampling increment which was consistent with sediment redistribution. The TOC-carbonate offsets, which are indicative of lateral advection and organic matter aging, were lower than those found in the majority of other regions, which was consistent with less lateral transport or a more oligotrophic setting. The magnitude in radiocarbon age offsets with depth could potentially be used as a relative aging or transport assessment tool in areas with little resuspension. VL - 193 UR - https://www.sciencedirect.com/science/article/pii/S0967063722002722 ER - TY - JOUR T1 - The southern Gulf of Mexico: A baseline radiocarbon isoscape of surface sediments and isotopic excursions at depth JF - PLOS ONE Y1 - 2020 A1 - Bosman, Samantha H. A1 - Schwing, Patrick T. A1 - Larson, Rebekka A. A1 - Wildermann, Natalie E. A1 - Brooks, Gregg R. A1 - Romero, Isabel C. A1 - Sanchez-Cabeza, Joan-Albert A1 - Ruiz-Fernández, Ana Carolina A1 - Machain-Castillo, Maria Luisa A1 - Gracia, Adolfo A1 - Escobar-Briones, Elva A1 - Murawski, Steven A. A1 - Hollander, David J. A1 - Chanton, Jeffrey P. ED - Potter-McIntyre, Sally KW - Gulf of Mexico KW - hydrocarbons KW - Oil spills KW - Oils KW - Petroleum KW - Sediment AB - The southern Gulf of Mexico (sGoM) is home to an extensive oil recovery and development infrastructure. In addition, the basin harbors sites of submarine hydrocarbon seepage and receives terrestrial inputs from bordering rivers. We used stable carbon, nitrogen, and radiocarbon analyses of bulk sediment organic matter to define the current baseline isoscapes of surface sediments in the sGoM and determined which factors might influence them. These baseline surface isoscapes will be useful for accessing future environmental impacts. We also examined the region for influence of hydrocarbon deposition in the sedimentary record that might be associated with hydrocarbon recovery, spillage and seepage, as was found in the northern Gulf of Mexico (nGoM) following the Deepwater Horizon (DWH) oil spill in 2010. In 1979, the sGoM experienced a major oil spill, Ixtoc 1. Surface sediment δ13C values ranged from -22.4‰ to -19.9‰, while Δ14C values ranged from -337.1‰ to -69.2‰. Sediment δ15N values ranged from 2.8‰ to 7.2‰, while the %C on a carbonate-free basis ranged in value of 0.65% to 3.89% and %N ranged in value of 0.09% to 0.49%. Spatial trends for δ13C and Δ14C were driven by water depth and distance from the coastline, while spatial trends for δ15N were driven by location (latitude and longitude). Location and distance from the coastline were significantly correlated with %C and %N. At depth in two of twenty (10%) core profiles, we found negative δ13C and Δ14C excursions from baseline values in bulk sedimentary organic material, consistent with either oil-residue deposition or terrestrial inputs, but likely the latter. We then used 210Pb dating on those two profiles to determine the time in which the excursion-containing horizons were deposited. Despite the large spill in 1979, no evidence of hydrocarbon residue remained in the sediments from this specific time period. VL - 15 UR - https://www.ncbi.nlm.nih.gov/pubmed/32294128 IS - 4 ER - TY - JOUR T1 - Sedimentation Pulse in the NE Gulf of Mexico following the 2010 DWH Blowout JF - PLOS ONE Y1 - 2015 A1 - Brooks, Gregg R. A1 - Larson, Rebekka A. A1 - Schwing, Patrick T. A1 - Romero, Isabel A1 - Moore, Christopher A1 - Reichart, Gert-Jan A1 - Jilbert, Tom A1 - Chanton, Jeff P. A1 - Hastings, David W. A1 - Overholt, Will A. A1 - Marks, Kala P. A1 - Kostka, Joel E. A1 - Holmes, Charles W. A1 - Hollander, David ED - Chin, Wei-Chun AB - The objective of this study was to investigate the impacts of the Deepwater Horizon (DWH) oil discharge at the seafloor as recorded in bottom sediments of the DeSoto Canyon region in the northeastern Gulf of Mexico. Through a close coupling of sedimentological, geochemical, and biological approaches, multiple independent lines of evidence from 11 sites sampled in November/December 2010 revealed that the upper ~1 cm depth interval is distinct from underlying sediments and results indicate that particles originated at the sea surface. Consistent dissimilarities in grain size over the surficial ~1 cm of sediments correspond to excess 234Th depths, which indicates a lack of vertical mixing (bioturbation), suggesting the entire layer was deposited within a 4–5 month period. Further, a time series from four deep-sea sites sampled up to three additional times over the following two years revealed that excess 234Th depths, accumulation rates, and 234Th inventories decreased rapidly, within a few to several months after initial coring. The interpretation of a rapid sedimentation pulse is corroborated by stratification in solid phase Mn, which is linked to diagenesis and redox change, and the dramatic decrease in benthic formanifera density that was recorded in surficial sediments. Results are consistent with a brief depositional pulse that was also reported in previous studies of sediments, and marine snow formation in surface waters closer to the wellhead during the summer and fall of 2010. Although sediment input from the Mississippi River and advective transport may influence sedimentation on the seafloor in the DeSoto Canyon region, we conclude based on multidisciplinary evidence that the sedimentation pulse in late 2010 is the product of marine snow formation and is likely linked to the DWH discharge. VL - 10 UR - http://dx.plos.org/10.1371/journal.pone.0132341 IS - 7 ER -