Friday, October 28, 2011
Hall 1-2 (San Jose Convention Center)
On April 20, 2010, the United States was faced with one of the greatest environmental disasters of all time: the BP Deepwater Horizon oil spill in the Gulf of Mexico. This disaster released approximately 4.4 million barrels of oil and 300,000 tons of natural gas into the ocean. Most of this natural gas, consisting primarily of methane, ethane, and propane, dissolved in the deep ocean to form layered plumes that fueled intense bacterial respiration and a consequent decrease in oxygen throughout the region. This work targeted the water column to constrain the maximum rate of bacterial respiration of the natural gas plume. A novel method using uniformly 13C-labeled substrates as tracers was applied to determine the rate of microbial consumption of these gases in water surrounding the impacted area. Experiments were performed on board the R/V Cape Hatteras (June 12–20, 2010) and the NOAA vessel Pisces (September 7-17, 2010); samples were analyzed using an isotope ratio mass spectrometer (IRMS). Respiration rates in younger versus older plumes measured in June revealed that marine bacteria consumed propane, ethane, and methane, in order of preference with turnover times of 2-25 days, 40-200 days, >300 days, respectively. By September, with three more months of bacterial growth and gas consumption, marine bacteria had exhausted all the gas which had dissolved in layered plumes and prevented this large source of greenhouse gases from entering the atmospheric reservoir.