Award: OCE-1045330

RAPID Deepwater Horizon Oil Spill: Marine Snow and Sedimentation Uta Passow, Vernon Asper and Arne Diercks It is important to understand the distribution of the accidentally released oil after the explosion of the Deep Water Horizon rig in the Gulf of Mexico (GoM) in April 2010. Damage assessment and mediation can only be achieved if we understand the pathway of the oil in the environment and through ecosystems. The released oil consisted of a mixture of chemically very diverse substances. Some of these fractions of the oil reached the surface, whereas other fractions remained at different depths, some forming a subsurface plume at about a 1000m. What is the fate of these different fractions of the spilled oil? At the surface we observed the formation of cm-sized very mucus-rich marine snow in the vicinity of the oil slicks. Within our NSF funded project we investigated how this marine snow may have formed. Experimentally we simulated different environmental conditions to determine which circumstances promote the formation of such large mucus rich marine snow. Spider-web like mucus webs formed in our experiments at the water-oil-air interface in the presence of aged oil from the spill, but not in the presence of sterile, non-weathered oil. We suggest that the presence of specific bacteria combined with environmental conditions favorable to these organisms resulted in the formation of these mucus webs. The mucus webs collapsed as they aged. The resulting marine snow looked like that observed in the GoM near the oil. Similar mucus rich marine snow was also formed when phytoplankton, especially the blue-green algae Trichodesmium spp. aggregated including oil droplets within the aggregates. In the absence of oil such aggregates remained green and algae viable and identifiable. In the presence of oil, however, these algae were decomposed rapidly and within hours mucus rich marine snow was formed. Both of these mechanisms presumably contributed to the formation of the large amount of mucus rich marine snow in the vicinity of the oil spill. Our research within this project furthermore suggests that the marine snow displayed high (100Æs meters per day) sinking velocities when aged. This was observed on snow formed in experiments and on snow collected from the surface waters of the GOM after the spill. We thus believe that at least some of the marine snow in the GoM sank to the seafloor, where it was deposited. Many marine organisms feed on marine snow and another fraction of this sinking marine snow was presumably eaten during transit and entered the food chain. Our colleagues have tracked the signature from the oil into the food web of the GoM. Within our project we also deployed a funnel-shaped particle interceptor trap, which collects sinking particles. This trap was deployed near the site of the accident after the spill, just above the sea floor and collected sinking particles continuously for 15 months. Currently these twenty samples which represent twenty 3-week collection intervals are being analyzed. The data from these traps will reveal how much oil and dispersant reached the seafloor and when it arrived there. It will also show us if large sinking events, e.g. from affected organisms, were the consequence of the spill. Last Modified: 07/03/2012 Submitted by: Uta D E Passow