HR: 15:10h
AN: OS42B-07    [PDF]
TI: The Extent of CH$_{4}$ Emission and Oxidation in Thermogenic and Biogenic Gas Hydrate Environments
AU: Kastner, M
EM: mkastner@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, CA 92093-0212 United States
AU: * Solem, C
EM: rsolem@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, CA 92093-0212 United States
AU: Bartlett, D
EM: dbartlett@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, CA 92093-0212 United States
AU: MacDonald, I
EM: imacdonald@falcon.tamucc.edu
AF: Texas A&M University, Corpus Christi, 6300 Ocean Drive, Corpus Christi, TX 78412 United States
AU: Valentine, D
EM: dvalentine@alphahelix.seanet.int
AF: University of California, Santa Barbara, Department of Earth Sciences, Santa Barbara, CA 93106 United States
AB: The role of methane hydrate in the global methane budget is poorly understood, because relatively little is known about the transport of gaseous and dissolved methane through the seafloor into the ocean, from the water column into the atmosphere, and the extent of water-column methanotrophy that occurs en route. We characterize the transport and consumption of methane in three distinct gas hydrate environments, spanning the spectrum of thermogenic and biogenic methane occurrences: Bush Hill in the Gulf of Mexico, Eel River off the coast of Northern California, and the Noth and South Hydrate Ridges on the Cascadia Oregon margin. At all the sites studied a significant enrichment in $\delta^{13}$CH$_{4}$ with distance along isopycnals away from the methane source is observed, indicative of extensive aerobic bacterial methane oxidation in the water column. The effects of this process are principally pronounced in the mostly biogenic methane setting, with $\delta^{13}$C-CH$_{4}$ measured as high as -12 permil (PDB) between North and South Hydrate Ridge. The $\delta^{13}$C-CH$_{4}$ values ranged from -12 to -67 permil at Hydrate Ridge, -34 to -52 permil at Eel River, and -41 to -49 permil at Bush Hill. The large variation in methane carbon isotope ranges between the sites suggest that major differences exist in both the rates of aerobic methane oxidation and system openness at the studied locations. A mean kinetic isotope fractionation factor is being determined using a closed-system Rayleigh distillation model. An approximate regional methane flux from the ocean into the atmosphere is being estimated for the Gulf of Mexico, by extrapolation of the flux value from the Bush Hill methane plume over 390 plume locations having persistent oil slicks on the ocean surface, mapped by time series satellite data.
DE: 4805 Biogeochemical cycles (1615)
DE: 4806 Carbon cycling
DE: 4820 Gases
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting