Fallout plume of submerged oil from Deepwater Horizon.

ABSTRACT: The sinking of the Deepwater Horizon in the Gulf of Mexico led to uncontrolled emission of oil to the ocean, with an official government estimate of ? 5.0 million barrels released. Among the pressing uncertainties surrounding this event is the fate of ? 2 million barrels of submerged oil thought to have been trapped in deep-ocean intrusion layers at depths of ? 1,000-1,300 m. Here we use chemical distributions of hydrocarbons in >3,000 sediment samples from 534 locations to describe a footprint of oil deposited on the deep-ocean floor. Using a recalcitrant biomarker of crude oil, 17?(H),21?(H)-hopane (hopane), we have identified a 3,200-km(2) region around the Macondo Well contaminated by ? 1.8 ± 1.0 × 10(6) g of excess hopane. Based on spatial, chemical, oceanographic, and mass balance considerations, we calculate that this contamination represents 4-31% of the oil sequestered in the deep ocean. The pattern of contamination points to deep-ocean intrusion layers as the source and is most consistent with dual modes of deposition: a "bathtub ring" formed from an oil-rich layer of water impinging laterally upon the continental slope (at a depth of ? 900-1,300 m) and a higher-flux "fallout plume" where suspended oil particles sank to underlying sediment (at a depth of ? 1,300-1,700 m). We also suggest that a significant quantity of oil was deposited on the ocean floor outside this area but so far has evaded detection because of its heterogeneous spatial distribution.

SUBMITTER: Valentine DL 

PROVIDER: S-EPMC4234598 | biostudies-literature | 2014 Nov

REPOSITORIES: biostudies-literature