David Valentine has been studying the aftermath of the 2010 Deepwater Horizon oil blowout ever since the disaster killed 11 Macondo well workers and sent about 4.1 million barrels of oil into the Gulf of Mexico. A recognized expert in subsea oil, during 2015’s Refugio Oil Spill in Santa Barbara, the UCSB Earth Sciences and Marine Institute professor would often return calls and emails to reporters from his ship’s berth along the Gulf. One of the larger questions from the Macondo blowout was what would happen to such a quantity of oil in the deep, cold ocean. The results from the first four years of his team’s research on the fate of that oil appeared in November’s Proceedings of the National Academy of Sciences (PNAS) in a paper titled “Persistence and biodegradation of oil at the ocean floor following Deepwater Horizon.”
Valentine’s group, which included lead author Sarah Bagby, a postdoc at the Valentine Lab at the time, identified “compound-specific rates of biodegradation for 125 aliphatic, aromatic, and biomarker petroleum hydrocarbons,” as its abstract summarizes. The massive quantity of research data was examined chiefly by Bagby, now an assistant professor at Case Western Reserve in Cleveland, Ohio, in order to first identify Macondo oil “biomarkers” — no easy feat when the spilled oil was flowing from below-ground as do natural seeps — and then how each of the 125 hydrocarbon components broke down over the four-year study. At the time, the degrading of oil from shallower-water spills had been studied, but the Macondo oil, which was being pulled out at roughly 1,500 meters below sea level, was uncharted territory.
The oil, which flowed from the sheared well pipe for a total of 87 days, was skimmed from the surface, accumulated in the water column, or washed ashore and biodegraded. About half is assumed to have settled on the seafloor, the study states, mostly within about 5 kilometers of the well. The team’s samples, collected with submersibles, included the deep plume fallout, or a 3,200 square-kilometer deposition “footprint” extending to the southwest from the wellhead.