The 2010 BP Deepwater Horizon Oil spill dumped more than 200 million gallons of oil into the Gulf of Mexico yet government assessments have been unable to account for all of it.

Microbes likely processed most of the oil within months of the spill, but not all of it. A new hypothesis suggests the oil acted as a catalyst for plankton and other surface materials to clump together and fall to the sea floor in a massive sedimentation event - what they have termed a "dirty blizzard."

 The Deep-C (Deep Sea to Coast Connectivity in the Eastern Gulf of Mexico) Consortium is composed of 10 major institutions 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. They presented the dirty blizzard hypothesis at a recent conference in New Orleans that focused on the effects of the oil spill on the Gulf of Mexico ecosystem. The consortium came up with the never-before-observed dirty blizzard hypothesis by using thorium, lead and radiocarbon isotopes in addition to DNA analyses of sediments.

"Some of the missing oil may have mixed with deep ocean sediments, creating a dirty bathtub effect," said  Jeff Chanton, Professor of Oceanography at Florida State University. "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 oily sediments deposited on the sea floor could cause significant damage to ecosystems and may affect commercial fisheries in the future, he 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.

Deep-C is continuing their research to determine exactly how much of the oil ended up on the sea floor.