Undersea plumes of oil and dissolved gas and sedimented oil along the seafloor alter the ocean system following the BP oil well blowout. (Invited)

The explosion and subsequent sinking of the Deepwater Horizon drilling rig resulted in a deepwater blowout that injected vast quantities of crude oil and low molecular weight hydrocarbon gases into Gulf of Mexico for almost three months. The depth of the blowout (1500m), the rate of oil and gas injection, and the duration of the event underscore the unprecedented nature of this environmental disaster. While most of the released crude oil reached the ocean surface, generating massive surface slicks, some of the oil was trapped in extensive undersea plumes. These oil plumes occupied discrete layers of varying thickness between 1000 and 1300m water depth to the southwest of the wellhead. Unlike the crude oil, the vast majority of methane released from the wellhead appears to have dissolved into the deep cold seawater: concentrations of thermogenic gases (methane, ethane, propane, butane and pentane) were 10,000 to 1,000,000 times higher than previous concentrations measured at similar depths in the Gulf of Mexico. Very little gas appears to have fluxed to the atmosphere; most of the released gas was trapped in the undersea plumes. The injection of hydrocarbons into undersea plumes generated a swift phylogenetic and metabolic response in the microbial community -- hydrocarbon degrading microorganisms flourished and rates of methane oxidation and oxygen consumption were elevated by several orders of magnitude relative to background rates. Oil on the surface ocean was weathered and dispersed, resulting in an “oil aggregate snow storm” on the seafloor. Oil deposition to the seafloor generated substantial changes in microbial community and patterns of microbial activity.