Oil Spill has profound effects on sedimentation rates in the Gulf

A recent study published in Deep-Sea Research II, conducted by researchers at Eckerd College, University of South Florida, and Franklin & Marshall College, characterizes the sedimentation geochemistry of cores from sites around the Deepwater Horizon Oil spill. The work done by this study is integral to understanding the progression of oil released by the spill, the effects this oil has on benthic ecosystems, and a mechanism for sedimentation of the oil and it’s byproducts.

Three sites in the NE Gulf of Mexico were sampled between August 2010 and August 2013. After pre-DHW baselines were determined, the three sites were studied over a three year period. Firstly, it was determined that an increase in sedimentation occurred following the event. A mechanism for this sedimentation has not been determined, but the authors of this study hypothesize that the “coagulation of phytoplankton with oil droplets, coagulation of suspended matter with the oil droplets, and production of mucosoid material from the degraders of the oil” produced marine snow that sunk rapidly to the bottom. It is also possible that the increase of outflow from the Mississippi River contributed to increased sedimentation as well.

Secondly, the geochemistry of the sediment was evaluated. Relative concentrations of Mn, Re, and Cd were used as a proxy to determine the redox state of sediments post-blowout. Observations suggest that concentrations of these elements differed from their baselines for two years after the event. During the third year they began to normalize towards pre-blowout levels. Increasing concentrations of Re resulted in increasingly reducing conditions within sediments. This also began to normalize after two years.

The alterations of redox conditions in the sediments of the NE Gulf of Mexico had an effect on the benthic ecosystems, specifically on densities of benthic foraminifera. Decreases in these densities were recorded in two sites in December 2010 and February 2011, where there was a significant increase in reducing conditions as shown by Mn depletion and Re enrichment.

To read the full article online, visit ScienceDirect