The major findings of this project are: 1) discovery of deepwater oil and gas plumes, 2) describing the evolution of the methane cycle following the blowout, and, 3) documenting rapid sedimentation of “oil snow” to the seafloor. 

During the R/V Pelican cruise, and later the NSF-funded R/V Walton Smith, we were the first researchers to document deepwater plumes enriched in oil and gas emanating from the ruptured Macondo wellhead (Diercks et al. 2010, Joye et al. 2011, Wade et al. 2012). The deepwater plumes contained elevated concentrations of oil components, including PAH and n-alkanes, relative to waters above or beneath the plumes (Wade et al. 2012). Concentrations of methane, ethane, propane, butane and pentane were 75000 times higher than those expected from equilibrium with the atmosphere and the ratios of the low molecular weight alkanes compared to that expected from solubility equilibrium with Macondo vent gas, as well as in situ digital images of gas hydrate flakes suspended in the water column hundreds of meters above the bottom, suggests that gas hydrate formed and persisted in the deepwater layers in which the gas and oil rich plume fluids were injected (Joye et al. 2011).

Time series sampling allowed us to track the fate of the plumes over time. Methane concentration data revealed that focused gas-rich deep-water plumes were short-lived features; however, water column methane concentrations remained elevated over background throughout the study. High methane concentrations selected for a methane oxidizing bacterial population capable of extremely high oxidation rates – up to 5900 nmol L^-1 d^-1, the highest rates documented for the pelagic ocean – in the gas-rich deepwater plumes in late May. Rates decreased to <50 nmol L^-1 d^-1 by late June, when methane concentrations and oxidation activity were distributed throughout the water column. Known and novel methane oxidizers responded rapidly to methane injection and the precipitous decline in activity underscores the importance of physiological constraints and environmental factors in regulating the marine system response following large perturbations such as focused methane inputs from deep-water blowouts.

In early May, sediment samples were collected at 40 stations along a grid spanning a 40x40 mile area around the Macondo wellhead. None of the samples contained any evidence of recent sedimentation or oiling and rates of microbial activity, as well as geochemical signatures, suggested low activity, non-seep (e.g. none of the cores were collected from a natural hydrocarbon seep) background sediments. In contrast, during the August/September 2010 R/V Oceanus, and subsequently on the November/December 2010 R/V Atlantis and July 2011 R/V Endeavor cruises, re-sampling of the same stations documented a large area impacted by recent, rapid and significant sedimentation of layers containing weathered oil. These layers were characterized by high organic content, including oil components like PAH, the absence of meio- and macro- fauna, and extremely low rates of microbial activity. 

Two post doctoral associates, three graduate students, one undergraduate, and two technicians from UGA received scientific training and professional development opportunities through this award. Additional post docs and students from other Universities have worked up samples collected from the NSF-funded Walton Smith cruise. Post-doc Crespo-Medina has a paper in review and several others in preparation regarding the fate of Macondo methane following the blowout and describing changes in microbial community composition in both waters and sediments. Of all the young scientists influenced by this project, undergraduate student Mann was most certainly the most profoundly affected. The Walton Smith cruise was her...

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