RELATIONSHIPS OF GULF OF MEXICO SEAFLOOR CHARACTERISTICS WITH PETROLEUM HYDROCARBONS FOLLOWING THE DEEPWATER HORIZON OIL SPILL

The Gulf of Mexico (GoMx) is one of the most globally productive regions for offshore oil drilling and natural gas exploration and recovery. But in 2010, the Deepwater Horizon semi-submersible drilling rig exploded, burned for three days and sank, rupturing the riser and blowout protector. Over 4 million barrels of oil were released into the GoMx in the subsequent 84 days before the well head was capped. Some of this oil was buoyant enough to float to the surface, where it was removed via a myriad of techniques, but most importantly, a plume of oil remained at approximately 1,100m water depth, where it proceeded to drive a marine snow event and deposit large quantities of oil on the seafloor.

The seafloor of GoMx is complex, dynamic, and ever evolving. Submarine canyons, mounds, channels, salt domes, and knolls dominate the seafloor which can lead to an inaccurate and biased sampling of bottom sediments. Using high-resolution bathymetry data, relationships between total polycyclic aromatic hydrocarbons (TPAH), their fluxes, and inventories have been identified. Distance from the source (well) was a very important variable, and showed that stations closer to the source tended to have more oil on the seafloor. The slope of the seafloor did not show any significant relationships with higher concentrations of oil, but the aspect of these slopes relative to the well showed significant differences in concentrations of TPAHs. Station aspects facing directly opposite of the well head had significantly lower concentrations of TPAHs than stations facing directly at the well head, to the right, or to the left. Based on these observations, the distribution of TPAHs are influenced primarily by the linear distance from the source and the direction the seafloor slope is facing. These results suggest that complexity of ocean bottom topography did play a role in the distributions of oil on the seafloor.