Study Examines Sediment East of Deepwater Horizon for Oil-Associated Marine Snow

Eckerd College students transferring a multicore from a collection barrel to a working barrel aboard the R/V Weatherbird II, June 2011. (Photo provided by Gregg Brooks)

(Click to enlarge) Eckerd College students transferring a multicore from a collection barrel to a working barrel aboard the R/V Weatherbird II, June 2011. (Photo provided by Gregg Brooks)

Scientists analyzed sea floor sediment in the Gulf of Mexico’s DeSoto Canyon region to investigate potential oil spill impacts. Evidence from sedimentological, geochronological, geochemical, and biological sources pointed to a rapid, 4-5 month sedimentation event in late 2010.

The sediment’s top centimeter was distinct from underlying compositions, with deposited particles originating from the sea surface. Sediments below the top layer contained no evidence of similar events, suggesting that the sedimentation pulse was a unique occurrence coincident with marine snow formed during and after the Deepwater Horizon spill. They published their findings in PLOS One: Sedimentation Pulse in the NE Gulf of Mexico following the 2010 DWH Blowout.

Scientists have documented observations of an unusually large marine snow event after the oil spill with surface water particulates aggregating and then rapidly sinking to the sea floor.  Study author Gregg Brooks said that their research group observed increased sedimentation rates during the summer of 2010 and shifts in sediment characteristics in the fall. They analyzed sediment cores collected in November-December 2010 and cores collected over the next two years to determine a possible relationship among these observations. Differences in sediment types and sources on either side of the DeSoto Canyon made this an ideal region to investigate if the oil spill altered natural sedimentation patterns and processes.

Brooks described their study methods:  “The ultra-high-resolution (2mm) sampling and analysis was necessary to investigate sediments that were deposited over a very short (monthly) time frame.  Non-traditional uses of techniques, such as 234Th (thorium) for geochronology, were also necessary to detect the monthly-scale timing of events/processes following the initial spill.” 

Gregg Brooks (R) assists in retrieving a multicore aboard the R/V Weatherbird II, November 2010. (Photo courtesy of Ben Flower)

(Click to enlarge) Gregg Brooks (R) assists in retrieving a multicore aboard the R/V Weatherbird II, November 2010. (Photo courtesy of Ben Flower)

There were larger amounts of thorium and mass accumulation rates in sediments collected in late 2010/early 2011 relative to later collection periods. Consistent dissimilarities in grain size and natural abundance radiocarbon in earlier-collected sediments’ top-layer indicated a lack of vertical mixing or bioturbation, which corresponded to decreased benthic foraminifera densities. Manganese stratification provided evidence of redox change consistent with elevated sedimentation rates. There were substantial elevations in crude oil biomarker concentrations and photosynthetic organisms in cores’ top layer compared to levels of later-collected cores.

The team acknowledged that Mississippi river discharge, high seasonal coastal runoff, and lateral sediment transport could also explain the observed sedimentation event, although the study’s results were more consistent with a sedimentation pulse from the sea surface. Looking forward, Brooks commented, “This study refines the understanding of how and under what circumstances 234Th (thorium) can be utilized in deep sea environments and as a dating tool versus the traditional use as an indicator of bioturbation.”

The study’s authors (a collaboration among scientists and graduate and undergraduate students) are Gregg R. Brooks, Rebekka A. Larson, Patrick T. Schwing, Isabel Romero, Christopher Moore, Gert-Jan Reichart, Tom Jilbert, Jeff P. Chanton, David W. Hastings, Will A. Overholt, Kala P. Marks, Joel E. Kostka, Charles W. Holmes, and David Hollander.

This study’s datasets are publicly available through the Gulf of Mexico Research Initiative Information & Data Cooperative (GRIIDC) at:

A related study details sources, concentrations, and spatial variability of hydrocarbons deposited on the seafloor:  Romero, et al., PLoS ONE 2015

Read other articles related to oil-associated marine snow:

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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 Integrated Modeling and Analysis of Gulf Ecosystems (C-IMAGE I and C-IMAGE II), the Deepsea to Coast Connectivity in the Eastern Gulf of Mexico (Deep-C) consortium, and Florida Institute of Oceanography (FIO). Other funding sources included Environchron.

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 http://gulfresearchinitiative.org/.