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The Gulf Oil Spill Left More Damage Than We Previously Thought

Oil and other contaminates likely accumulated on the seafloor, according to a new report.

By Madeleine Thomas


(Photo: Justin E. Stumberg/U.S. Navy via Getty Images)

Oil and other contaminates from the Deepwater Horizon oil spill — one of the worst environmental disasters in history — likely lingered in the waters of the Gulf of Mexico for months longer than experts originally predicted, according to a new study published in the Proceedings of the National Academy of Sciences.

In the weeks following the spill, it appeared as though any traces of hydro- and petrocarbons from the oil had cleared from the Gulf’s surface waters. In actuality, according to the study, oil, black carbon, and drilling mud contaminates likely accumulated on the seafloor for months after the Macondo wellhead was finally capped. Until now, oil hasn’t typically been thought of as a substance that can sink to such great depths.

Blame marine snow, a naturally occurring slurry of phytoplankton, zooplankton feces, and other oceanic debris. As the “snow” sinks from the ocean’s surface waters, the mix picks up any suspended substances in its path — like oil spill contaminants — carrying them to the seafloor.

As much as 10 percent — or millions of gallons — of the oil spilled during the Deepwater disaster may have ended up on the Gulf’s seafloor.

Between August 2010 and October 2011, the research team collected water samples from a sediment trap set up 4.5 miles from the capped Macondo wellhead. They were able to link the hydrocarbons found in their samples to the same kind of crude oil that leaked from the Deepwater Horizon. The researchers dubbed the polluted marine snow a “dirty blizzard.”

According to this new analysis, black carbon — left over from burning oil slicks — kept accumulating on the Gulf’s seafloor for up to two months after the burns had stopped. Barium, a chemical additive used in mud drilling, remained on the seafloor for up to five additional months. As much as 10 percent — or millions of gallons — of the oil spilled during the Deepwater disaster may have ended up on the Gulf’s seafloor this way, the researchers estimate. Those contaminants likely entered the food web.

“Considering the widespread use of drilling mud at hundreds of ocean drilling sites around the world, the environmental implications of such an unexpectedly long residence time of barium in the water column is significant and worthy of further investigation,” the researchers write.

Linking dirty blizzards with seafloor oil accumulation could impact future spill responses and restoration efforts, the researchers note. “[T]ransport of oil-derived carbon to the seafloor was not one of the mechanisms accounted for in the reckoning of the oil spill calculator,” they write. “However, it will likely be taken into account in the future.”