Evidence That the Deepwater Horizon Oil Spill Caused Changes in Seasonal Mean Trace Metal Concentrations in Bottom Sediment Retrieved from the Eastern Outer Continental Shelf (OCS), Gulf of Mexico

Abstract:

Higher nickel, vanadium, and lead concentrations measured in sea bottom sediment of the eastern OCS can be explained by the presence of a new source for these metals from the damaged Mconco Well which resulted in the BP Deepwater Horizon Oil Spill during the spring of 2010. Sixty-five sediment samples were collected during the fall months for the years 2008-2011 from the eastern OCS. The Tukey range test was used to compare six metal concentrations between the relict sand deposits of the northern Gulf OCS to the relict carbonate sediments off of western Florida OCS. Tests indicated that nickel, vanadium, and lead were significantly higher (p < 0.05) in the seasonal mean concentrations in the relict sand deposits. These higher concentrations are also reflected in the vanadium to nickel ratio being statistically different (p < 0.005) for carbonate sediment (1.70 ± 0.24) when compared to relict sand (0.96 ± 0.12) in the north, which is closer to the damaged well. This difference indicates a new source of nickel that accumulated through time in the north. In the carbonate sediment there appears a zonation of the ratios with a dependency on water depth. The V/Ni ratio is 0.80 ± 0.10 for samples taken in water depths at or deeper than 200 m; and ratios are 2.06 ±0.42 for samples taken in water depths shallower than 200 m.