Nutrient depletion as a proxy for microbial growth in Deepwater Horizon subsurface oil/gas plumes

The Deepwater Horizon accident resulted in a substantial uncontrolled hydrocarbon release to the northern Gulf of Mexico, much of which was entrained in deep submerged plumes. While bio-degradation of the hydrocarbons has been inferred from microbial biomass and genetics, the amount of conversion of oil and gas carbon to biomass remains uncertain having only been estimated in modeling studies. Here we examine correlated depletions of nitrate, phosphate and oxygen in the submerged plumes and conclude that a substantial portion of hydrocarbons in these plumes was converted to biomass (0.8–2 × 1010 mol C). This contrasts with nutrient-limited surface waters where other work has suggested hydrocarbon-induced microbial growth to have been minimal. Our results suggest the need for better monitoring of changes in nutrients as well as study of nutrient recycling in similar future hydrocarbon releases. (letter)