Mapping spatial and temporal variation of seafloor organic matter Δ14C and δ13C in the Northern Gulf of Mexico following the Deepwater Horizon Oil Spill

Following the Deepwater Horizon oil spill of 2010, large amounts of biodegraded oil (petrocarbon) sank to the seafloor. Our objectives were to 1) determine post-spill isotopic values as the sediments approached a new baseline and 2) track the recovery of affected sediments. Sediment organic carbon Delta C-13 and Delta C-14 reached a post spill baseline averaging -21.2 +/- 0.9 parts per thousand (n = 129) and-220 +/- 66 parts per thousand (n = 95). Spatial variations in seafloor organic carbon baseline isotopic values, C-13 and C-14, were influenced by river discharge and hydrocarbon seepage, respectively. Inverse Distance Weighting of surface sediment Delta C-14 values away from seep sites showed a 50% decrease in the total mass of petrocarbon, from 2010 to 2014. We estimated a rate of loss of -2 x 10(9) g of petrocarbon-C/year, 2-11% of the degradation rates in surface slicks. Despite the observed recovery in sediments, lingering residual material in the surface sediments was evident seven years following the blowout.

Automated summary

Following the Deepwater Horizon oil spill of 2010, post-spill isotopic values of sediment organic carbon reached a new baseline, influenced by river discharge and hydrocarbon seepage. Spatial variations in seafloor organic carbon baseline isotopic values showed a 50% decrease in petrocarbon mass from 2010 to 2014. Despite observed recovery, residual material was still evident in surface sediments seven years after the blowout.