Macondo oil in deep-sea sediments: Part 1-sub-sea weathering of oil deposited on the seafloor

Chemical analysis of sediment cores collected up to 8 km from the Macondo well in 2010/2011 demonstrates the extent of weathering of the Macondo oil deposited in deep-sea sediments following the Deepwater Horizon disaster. On average, dissolution and biodegradation of the oil on the seafloor increased with distance from the well indicating that weathering occurred rapidly and overwhelmingly during the oil's transport as dispersed oil droplets within the deep-sea plume. Beyond about 5 km from the well, the oil deposited on the seafloor had lost most mass below C-25, was relatively enriched in n-C-25+ n-alkanes and C-3 and C-4-alkylated benz[a]anthracenes/chrysenes, the latter owing to 95% depletion of total PAHs. Biodegradation of C-28 and C-29 tricyclic terpanes, C-34 and C-35 17 alpha(H),21 beta(H)-homohopanes, C-27 13 beta(H),17 alpha(H)-dia and C-27 14 beta(H),17 beta(H)-steranes and dissolution of C-26 to C-29 triaromatic steroids occurred. The results provide a means to distinguish Macondo oil in deep-sea sediments from naturally-occurring seep oils and pervasive ambient background hydrocarbons. (C) 2016 Elsevier Ltd. All rights reserved.