Abstract or Keywords
The Deepwater Horizon oil spill (DWHOS) released an unprecedented amount of oil ( approximately 4.0 million barrels) at a depth of 1500 m, resulting in the formation of multiple hydrocarbon mixtures at the surface and within the water column (e.g., oil slicks, submerged plumes) due to distinct weathering processes in different water column compartments. Moreover, an unexpected and protracted sedimentation event was observed of oil-associated marine snow (MOS), and oil-mineral aggregates (OMAS) referred to as MOSSFA (marine oil snow sedimentation and flocculent accumulation). Although multiple studies have examined DWH oil residues across a broad range of environments, a comprehensive discussion of the role of the different hydrocarbon mixtures from the water column on sediment chemistry, oil-residues fate, and impacts is not available. Here, we present a wide range of chemical data and diagnostic ratios from sediment cores collected in the northern GoM to identify and quantify water column hydrocarbon mixtures in the sediment samples. Results indicate that larger amounts of deposited oil-residues came from the water column (e.g., OMAS), followed by the surface, and a small portion from the submerged plumes (53%, 46%, and 1% respectively, of the total amount of oil that remained in the environment after recovery efforts). These results demonstrate that most of the weathering of the spilled oil occurred before deposition and tight connectivity between the water column and the sedimentary environment. This water-sediment connectivity is critical for understanding the effect of other physical processes (e.g., resuspension) on redistribution of oil-residues on the seafloor. Furthermore, this approach can be used for forecasting the long-term fate of deposited oil-residues on the seafloor, critical during response and planning activities associated with oil spills at depth.