title: 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, 17α(H),21β(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.
authors.affiliation: Department of Earth Science and Marine Science Institute, University of California, Santa Barbara, CA 93106; valentine@geol.ucsb.edu.
authors.forename: David L
authors.initials: DL
authors.lastname: Valentine
authors.affiliation: Department of Earth Science and Marine Science Institute, University of California, Santa Barbara, CA 93106;
authors.forename: G Burch
authors.initials: GB
authors.lastname: Fisher
authors.affiliation: Department of Earth Science and Marine Science Institute, University of California, Santa Barbara, CA 93106;
authors.forename: Sarah C
authors.initials: SC
authors.lastname: Bagby
authors.affiliation: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole MA 02543; and.
authors.forename: Robert K
authors.initials: RK
authors.lastname: Nelson
authors.affiliation: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole MA 02543; and.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Reddy
authors.affiliation: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole MA 02543; and.
authors.forename: Sean P
authors.initials: SP
authors.lastname: Sylva
authors.affiliation: Department of Earth System Science, University of California, Irvine, CA 92697.
authors.forename: Mary A
authors.initials: MA
authors.lastname: Woo
keywords: Gulf of Mexico; Macondo Well blowout; deep plumes; ocean pollution; petroleum spill