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Miles of Gulf Seafloor Slick with Oil from BP Spill

Oct 30, 2014 01:07 PM EDT

Back in 2010, the infamous Deepwater Horizon oil spill gushed millions of barrels of oil into the Gulf of Mexico, but where a lot of that oil ended up remained a mystery. Now however, a large amount of that elusive oil has been found, coating miles of the Gulf seafloor, according to new research.

Between two and 16 percent of the total oil spilled sits just within 25 miles (40 kilometers) of the BP-operated Macondo well responsible for the environmental disaster.

"This analysis provides us with, for the first time, some closure on the question, 'Where did the oil go, and how did it get there?'" Don Rice, the program director of the National Science Foundation's (NSF) Division of Ocean Sciences, said in a statement.

Scientists estimate that about two million barrels of Deepwater Horizon oil ended up in the deep ocean, but tracing that oil has been challenging.

Led by microbial geochemist David Valentine from the University of California, Santa Barbara, and funded by the NSF, researchers gathered more than 3,000 samples from 534 locations. Through their analysis, they identified a 1,250-square-mile (3,237 square km) patch of seafloor slick with oil from the spill.

Evidence that this oil was specifically from the Macondo well came from the presence of hopane, a nonreactive hydrocarbon, in a thin layer at the bottom of the ocean.

"Based on the evidence, our findings suggest that these deposits are from Macondo oil that was first suspended in the deep ocean, then settled to the sea floor without ever reaching the ocean surface," Valentine said.

The droplets of oil started out 3,500 feet (1,067 meters) below the ocean surface before deep-ocean currents pushed them down another 1,000 feet (305 meters) to the seafloor.

"The pattern of contamination we observe is fully consistent with the Deepwater Horizon event but not with natural seeps," Valentine explained.

Much of the deep ocean oil is still missing, however, and what Valentine and his colleagues found is just a small portion. About 70 percent of the spilled oil is still floating around in the ocean somewhere, negatively affecting wildlife like dolphin and corals.

The findings appear in the journal Proceedings of the National Academy of Sciences.

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