The blowout of the Deepwater Horizon (DWH) drilling rig in 2010 released an unprecedented amount of oil at depth (1,500 m) into the Gulf of Mexico (GoM). Sedimentary geochemical data from an extensive area (∼194,000 km2) was used to characterize the amount, chemical signature, distribution, and extent of the DWH oil deposited on the seafloor in 2010-2011 from coastal to deep-sea areas in the GoM. The analysis of numerous hydrocarbon compounds (N = 158) and sediment cores (N = 2,613) suggests that, 1.9 ± 0.9 × 104 metric tons of hydrocarbons (>C9 saturated and aromatic fractions) were deposited in 56% of the studied area, containing 21± 10% (up to 47%) of the total amount of oil discharged and not recovered from the DWH spill. Examination of the spatial trends and chemical diagnostic ratios indicate large deposition of weathered DWH oil in coastal and deep-sea areas and negligible deposition on the continental shelf (behaving as a transition zone in the northern GoM). The large-scale analysis of deposited hydrocarbons following the DWH spill helps understanding the possible long-term fate of the released oil in 2010, including sedimentary transformation processes, redistribution of deposited hydrocarbons, and persistence in the environment as recycled petrocarbon.

Significance: Despite numerous publications reporting the accumulation of petroleum hydrocarbons associated with the Deepwater Horizon spill on the seafloor, the mechanisms of their delivery to the seafloor remain unclear. We demonstrate sedimentation of black carbon derived from the in situ burning of surface oil slicks for about 2 mo following the cessation of burning while other contaminants from the spill, including bioactive barium derived from drilling mud, continued to sediment for at least 5 mo after the well was capped. We also show that the episodic sinking of spill-associated substances was mainly mediated by marine particles, especially diatoms. Together, these data demonstrate delivery mechanisms of contaminants from the spill to benthic ecosystems in the deep Gulf of Mexico.