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US researchers have pinpointed the whereabouts of 2 million barrels of submerged oil in the Gulf of Mexico, spilt as a result of the Deepwater Horizon disaster in 2010, in an effort to pinpoint the exact environmental damage it caused.
The submerged oil represents more than a third of the 5 million barrels the United States government estimates the Macondo well discharged between the initial explosion in April 2010 until it was capped in July.
The researchers analysed data from more than 3,000 samples collected at 534 locations over 12 expeditions and identified a 1,250 square mile area of deep sea floor upon which up to 16% of the discharged oil was deposited.
The fallout of oil to the sea floor created thin deposits most intensive to the southwest of the Macondo well. The oil was most concentrated within the top half inch of the sea floor and was patchy even at the scale of a few feet.
David Valentine, professor of earth science and biology and a lead researcher on the project at UC Santa Barbara, said: “Based on the evidence, our findings suggest that these deposits come from Macondo oil that was first suspended in the deep ocean and then settled to the sea floor without ever reaching the ocean surface.
“The pattern is like a shadow of the tiny oil droplets that were initially trapped at ocean depths around 3,500 feet and pushed around by the deep currents. Some combination of chemistry, biology and physics ultimately caused those droplets to rain down another 1,000 feet to rest on the sea floor."
The investigation focused primarily on hopane, a nonreactive hydrocarbon that served as a proxy for the discharged oil.
Valentine and his colleagues fpimd hotspots of oil fallout in close proximity to damaged deep-sea corals, supporting previously disputed finding that these corals were damaged by the Deepwater Horizon spill. “The evidence is becoming clear that oily particles were raining down around these deep sea corals, which provides a compelling explanation for the injury they suffered," said Valentine.
While the study examined a specified area, the researchers conclude that the observed oil represents a minimum value and that oil deposition likely occurred outside the study area but so far has largely evaded detection because of its patchiness.
Don Rice, program director in the National Science Foundation's Division of Ocean Sciences, said: “This analysis provides us with, for the first time, some closure on the question 'Where did the oil go and how?' It also alerts us that this knowledge remains largely provisional until we can fully account for the remaining 70%"
BP, one of the operators of Deepwater Horizon, is still settling financial settlements for the oil spill in the US courts. Last week the oil firm announced its fourth oil discovery in the region, located 180 miles off the coast of Louisiana.