Sedimentation Pulse in the NE Gulf of Mexico following the 2010 DWH Blowout

RESEARCH ARTICLE Sedimentation Pulse in the NE Gulf of Mexico following the 2010 DWH Blowout Gregg R. Brooks1*, Rebekka A. Larson1,2, Patrick T. Schwing2, Isabel Romero2, Christopher Moore1, Gert-Jan Reichart3,4, Tom Jilbert3, Jeff P. Chanton5, David W. Hastings1, Will A. Overholt6, Kala P. Marks6, Joel E. Kostka6,7, Charles W. Holmes8, David Hollander2 1 Department of Marine Science, Eckerd College, Saint Petersburg, FL, United States of America, 2 College of Marine Science, University of South Florida, Saint Petersburg, FL, United States of America, 3 Department of Earth Science, Utrecht University, Utrecht, The Netherlands, 4 Marine Geology Department, Royal Netherlands Institute for Sea Research, Texel, The Netherlands, 5 Department of Earth, Ocean & Atmospheric Science, Florida State University, Tallahassee, FL, United States of America, 6 Schools of Biology, Georgia Institute of Technology, 310 Ferst Drive, Atlanta, Georgia 30332–0230, United States of America, 7 Schools of Earth & Atmospheric Sciences, Georgia Institute of Technology, 310 Ferst Drive, Atlanta, Georgia, 30332–0230, United States of America, 8 Environchron, 9103 64th Ave. E., Bradenton, FL, United States of America * (GB) OPEN ACCESS Citation: Brooks GR, Larson RA, Schwing PT, Romero I, Moore C, Reichart G-J, et al. (2015) Sedimentation Pulse in the NE Gulf of Mexico following the 2010 DWH Blowout. PLoS ONE 10(7): e0132341. doi:10.1371/journal.pone.0132341 Editor: Wei-Chun Chin, University of California, Merced, UNITED STATES Received: February 10, 2015 Accepted: June 12, 2015 Published: July 14, 2015 Copyright: © 2015 Brooks 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. Data Availability Statement: (https://data. gulfresearchinitiative.org) (https://data. gulfresearchinitiative.org/data/Y1.x031.000:0001) (https://data.gulfresearchinitiative.org/data/Y1.x031. 000:0002) (https://data.gulfresearchinitiative.org/data/ Y1.x031.000:0003). Funding: Funding was provided by the Gulf of Mexico Research Initiative (http:// gulfresearchinitiative.org) through the Florida Institute of Oceanography (http://www.fio.usf.edu), Center for Integrated Modeling and Analysis of Gulf Ecosystems (http://www.marine.usf.edu/c-image/), and Deepsea to Coast Connectivity in the Eastern Gulf of Mexico Abstract 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 deepsea 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. PLOS ONE | DOI:10.1371/journal.pone.0132341 July 14, 2015 1 / 24 Sedimentation Pulse following the 2010 DWH Blowout (http://deep-c.org) consortia. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Environchron provided support in the form of salaries for authors C.W.H., but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section. Competing Interests: Environchron provided support in the form of salaries for authors C.W.H., but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section. Regarding the adherence to all PLOS ONE policies on sharing data and materials the authors would like to confirm that Environchron does not alter their adherence to PLOS ONE policies on sharing data and materials. Introduction The 2010 Deepwater Horizon (DWH) blowout event discharged >600 million L of oil and large quantities of natural gas (e.g., methane, ethane, butane, propane) into NE Gulf of Mexico (GoM) waters over an ~3-month period [1–4]. In addition, almost 7 million L of chemical dispersants were injected into the deep-sea environment for the first time at such a great depth (~1500 m) [5–7]. It is estimated that at least 60% of the oil released reached the sea surface where it was subjected to a variety of processes including biotic and abiotic reactions, cleanup activities, transport out of the study area or to nearby beaches by physical processes, evaporation, and settling to the sea floor [5, 7, 8]. The remaining ~40% of the oil and an unknown quantity of the deep injected dispersants never reached the surface and remain unaccounted for [5, 9]. An oil slick was detected in open marine and coastal surface waters from Louisiana to Florida, including the DeSoto Canyon region (Fig 1) [10, 11]. Subsurface hydrocarbon-rich plumes were initially detected to the southwest of the wellhead at depths between ~1000 and 1200 m, with a more diffuse plume identified between ~50 and 500 m [1, 4, 6, 9, 12]. Later, subsurface plumes were identified between ~1000 and 1400 m, and ~400 m to the northeast of the wellhead, in the DeSoto Canyon region [13]. An unusually large marine snow event was documented in oil contaminated surface waters following the blowout [14]. The marine snow may have formed from extracellular polysaccharides and oth (...truncated)