A “dirty blizzard” of sediment was the end result of the oil from the 2010 Deepwater Horizon spill acting as a catalyst for plankton and other surface materials to clump together and fall to the sea floor.

The dirty blizzard phenomenon may explain what happened to some portion of the more than 200 million gallons of spilled oil. Microbes likely processed most of the oil within months of the spill, but government assessments have not accounted for all of the spilled oil.

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“Some of the missing oil may have mixed with deep ocean sediments, creating a dirty bathtub effect,” said Jeff Chanton, the John Widmer Winchester Professor of Oceanography in the Department of Earth, Ocean and Atmospheric Science at Florida State University and one of the members of the Deep-C Consortium who presented the dirty blizzard hypothesis at a conference in New Orleans that focused on the effects of the oil spill on the Gulf of Mexico ecosystem. “The sediments then fell to the ocean floor at a rate 10 times the normal deposition rates. It was, in essence, an underwater blizzard.”

The consortium confirmed the never before observed dirty blizzard hypothesis by using thorium, lead and radiocarbon isotopes in addition to DNA analyses of sediments.

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The oily sediments deposited on the sea floor could cause significant damage to ecosystems and may affect commercial fisheries in the future, Chanton said.

The dirty blizzard hypothesis explains why layers of water that would normally be cloudy with suspended plankton instead appeared transparent during the spill, except for strings of particles falling to the bottom.

“The oil just sucked everything out of the surface,” Chanton said.

Chanton and his Deep-C colleagues are continuing their research to determine exactly how much of the oil ended up on the sea floor.

The Deep-C (Deep Sea to Coast Connectivity in the Eastern Gulf of Mexico) Consortium consists of 10 major institutions, including FSU, Eckerd College, the University of South Florida and Georgia Institute of Technology, involved in a long-term, interdisciplinary study of deep sea to coast connectivity in the northeastern Gulf of Mexico. The study is investigating the environmental consequences of the 2010 oil spill on living marine resources and ecosystem health. The spill left 11 dead and devastated the Gulf Coast environment.

The research was possible in part by the Gulf of Mexico Research Initiative (GoMRI), a 10-year independent research program investigating the effects of the Deepwater Horizon incident.

The mission of the GoMRI is to improve society’s ability to understand and mitigate the impacts of hydrocarbon pollution and stressors on the marine environment and public health. The program started up through a $500 million financial commitment from BP.

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