Droplets of weathered Macondo crude oil continued to sink to 1400 m for one year after the spill ended.
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The lack of evaporation and photooxidation indicated sinking of weathered oil that had lingered in the water column.
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Marine snow, especially diatom aggregates transported oil droplets to depth, but there was no evidence of soluble oil hydrocarbons that would have been sorbed to surfaces.
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The oil itself did not directly cause the formation of these marine snow aggregates.
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Priority Pollutant PAH-rich combustion particles stemming from in situ burning, was also transported to depth.
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.
