Study Describes Six-Year Evolution of Gulf Sediments Following Deepwater Horizon

Eckerd College's Rebekka Larson retrieves sediment collected November 2010 using an Ocean Instruments MC-800 aboard the R/V Weatherbird II. The sediment cores are used to investigate sedimentary impacts of the 2010 Deepwater Horizon incident. Photo credit: Patrick Schwing.

Eckerd College’s Rebekka Larson retrieves sediment collected November 2010 using an Ocean Instruments MC-800 aboard the R/V Weatherbird II. The sediment cores are used to investigate sedimentary impacts of the 2010 Deepwater Horizon incident. Photo credit: Patrick Schwing.

Scientists adapted high-resolution sampling and analyses methods to assess Gulf of Mexico sediment core samples collected from 2010-2016 and identify sedimentation changes that followed Deepwater Horizon. Their analyses showed that the spill led to a short-lived (less than 1 year) marine oil snow pulse that settled to the seafloor. That depositional event had detectable impacts for more than three years (indicated by higher sedimentation rates and an absence of bioturbation as compared to subsequent years), which was then followed by a return to normal sedimentation and biological activity.

The researchers published their findings in Anthropocene: High-resolution investigation of event driven sedimentation: Northeastern Gulf of Mexico

The 2010 Deepwater Horizon incident provided a unique opportunity to investigate the sedimentary impacts of a singular event in real time. The surface oil slick combined with biogenic and lithogenic particles and exopolymeric substances, resulting in a marine snow event that transported oil spill material to the sea floor (Anthropocene Daly et al., 2016). This study sought to understand the natural sedimentary environment before the marine snow event and determine how and to what magnitude the event affected the environment.

“Sediment cores record the history of an environment and, when there is a specific event, it can provide pre-event or baseline data,” explained study author Rebekka Larson. “Being able to combine sedimentation analysis on a monthly-scale with annual to decade scales allowed us to understand the immediate response of the environment as well as recovery and longer-term implications.”

The team built upon previously reported short-lived radioisotopes and sedimentology data derived from core samples collected in 2010 – 2011 (PLOS One Brooks et al., 2015) by applying  high-resolution analyses of sediment cores collected then and to new core samples collected through 2016. Using gamma spectrometry on Series HPGe (High-Purity Germanium) Coaxial Planar Photon Detectors, the team characterized the sedimentary signature and geochronology and accumulation rates (through Lead-210 or 210Pbxs and Thorium-234 or 234Thxs measurements).

“For short time-scale events such as the oil spill (months), it is critical to do high-resolution analyses to provide the highest potential to measure impacts of these events in sediments,” explained Larson. “This work focused on providing age control for short-term sedimentation in sediment cores following the spill and how it evolved over the subsequent six years. We sampled at 2mm resolution, which is not done in traditional sediment studies. This unique ‘time-series’ approach provided an understanding on how the sedimentary system evolved following this event, which would not be detectable using a traditional approach for investigating sediment core records.”

Larson said that this research can help future modeling efforts by defining oil spill impacts, especially those associated with marine oil snow sedimentation events. “This information can assist in predicting benthic impacts for different scenarios/events such as enhanced or reduced MOSSFA [Marine Oil Snow Sedimentation and Flocculent Accumulation]. This also assists decision-making and response during events with modeled predictions of oil spill distribution and MOSSFA generation being translated to potential consequences and distribution on the seafloor.”

Larson said that this study is an example of how a specific event can push science forward, advancing and adapting approaches and interpretations. “The refinement and application of high-resolution methods and techniques were required to identify the sedimentation from the oil spill event in the deep sea,” explained Larson. “Without these methods, the impact to deep-sea sediments and biology would not have been as fully understood. A key factor for this study’s success was that we did not know exactly what to do or what to measure, which allowed for adaptation and advances as we determined what was important to measure and how to do it well. This was particularly true for the short-term (months) age control using 234Thxs, which defined the sedimentation pulse associated with the oil spill.”

Larson acknowledged that a critical component for this study was the fast response to the spill and the continued funding to get the samples/analyses needed to characterize the sedimentary response, recovery, and stabilization. “The ten years of funding provided through the Gulf of Mexico Research Initiative made possible a more detailed understanding of the Gulf of Mexico than is traditionally possible through scientific funding opportunities. This funding became much larger than the Deepwater Horizon oil spill and created a greater understanding of the Gulf of Mexico ecosystem and improved scientific response and investigation of oil spills. During this time, there have been advances in techniques and methods and an increased scientific understanding of the Gulf of Mexico in a way that connects biology, geology, chemistry, and physical oceanography.”

Data are publicly available through the Gulf of Mexico Research Initiative Information and Data Cooperative (GRIIDC) at doi:10.7266/N7FJ2F94, doi:10.7266/N79S1PJZ, and doi:10.7266/N7610XTJ.

The study’s authors are Rebekka A. Larson, Gregg R. Brooks, Patrick T. Schwing, Charles W. Holmes, Savannah R. Carter, and David J. Hollander.

By Nilde Maggie Dannreuther. Contact maggied@ngi.msstate.edu with questions or comments.

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This research was made possible in part by a grant from the Gulf of Mexico Research Initiative (GoMRI) to the Center for the Integrated Modeling and Analysis of Gulf Ecosystems III (C-IMAGE III), Center for the Integrated Modeling and Analysis of Gulf Ecosystems II (C-IMAGE II), Center for the Integrated Modeling and Analysis of Gulf Ecosystems (C-IMAGE), and the Deepsea to Coast Connectivity in the Eastern Gulf of Mexico (DEEP-C) consortium.

The Gulf of Mexico Research Initiative (GoMRI) is a 10-year independent research program established to study the effect, and the potential associated impact, of hydrocarbon releases on the environment and public health, as well as to develop improved spill mitigation, oil detection, characterization and remediation technologies. An independent and academic 20-member Research Board makes the funding and research direction decisions to ensure the intellectual quality, effectiveness and academic independence of the GoMRI research. All research data, findings and publications will be made publicly available. The program was established through a $500 million financial commitment from BP. For more information, visit https://gulfresearchinitiative.org/.

© Copyright 2010-2019 Gulf of Mexico Research Initiative (GoMRI) – All Rights Reserved. Redistribution is encouraged with acknowledgement to the Gulf of Mexico Research Initiative (GoMRI). Please credit images and/or videos as done in each article. Questions? Contact web-content editor Nilde “Maggie” Dannreuther, Northern Gulf Institute, Mississippi State University (maggied@ngi.msstate.edu).