Character and sedimentation of “lingering” Macondo oil to the deep-sea after the Deepwater Horizon oil spill

Abstract

During the active 87-day Deepwater Horizon spill in the northern Gulf of Mexico, a significant fraction of the spilled Macondo oil was transported to the seafloor via the sedimentation of marine snow. Here we present a detailed characterization of oil that arrived together with marine snow at a 1400 m deep sediment trap six weeks to 13 months after the spill had ended. These data give insight into the nature and evolution of the sedimentation of the marine snow and oil, the latter of which remained as droplets in the water column after the spill ended. Four pulses of oil flux were recognized; three of which were associated with peak sedimentation rates of diatoms. Detailed chemical analysis (TPH, alkylated PAH, and petroleum biomarker fingerprints) reveal the sinking oil's lack of evaporation and photo-oxidation, which indicated it was not derived from the sea surface but had “lingered” within the water column after the spill. Measurable amounts of the increasingly weathered (biodegraded and water-washed) Macondo oil was collected in the trap for ~1 year after the active spill ended, over which time the oil flux decreased overall. The results indicate that sinking diatom aggregates and other marine snow scavenged measurable amounts of weathered Macondo oil droplets remaining in the water, and carried them to the deep-seafloor for approximately 1-year after the spill ended.