HR: 0830h
AN: B51C-0976    [PDF]
TI: A laboratory study of anaerobic oxidation of methane in the presence of methane hydrate
AU: * Solem, R
EM:
AF: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0202 United States
AU: Bartlett, D
EM: dbartlett@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0202 United States
AU: Kastner, M
EM: mkastner@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0202 United States
AU: Valentine, D
EM: valentine@geol.ucsb.edu
AF: Department of Geological Sciences, University of California, Santa Barbara, Santa Barbara, CA 93106 United States
AB: In order to mimic and study the process of anaerobic methane oxidation in methane hydrate regions we developed four high-pressure anaerobic bioreactors, designed to incubate environmental sediment samples, and enrich for populations of microbes associated with anaerobic methane oxidation (AMO). We obtained sediment inocula from a bacterial mat at the southern Hydrate Ridge, Cascadia, having cell counts approaching 10$^{10}$ cells/cc. Ultimately, our goal is to produce an enriched culture of these microbes for characterization of the biochemical processes and chemical fluxes involved, as well as the unique adaptations required for, AMO. Molecular phylogenetic information along with results from fluorescent {\it in situ} hybridization indicate that consortia of Archaea and Bacteria are present which are related to those previously described for marine sediment AMO environments. Using a medium of enriched seawater and sediment in a 3:1 ratio, the system was incubated at $4\deg$C under 43 atm of methane pressure; the temperature and pressure were kept constant. We have followed the reactions for seven months, particularly the vigorous consumption rates of dissolved sulfate and alkalinity production, as well as increases in HS-, and decreases in Ca concentrations. We also monitored the dissolved inorganic C (DIC) $\delta^{13}$C values. The data were reproduced, and indicated that the process is extremely sensitive to changes in methane pressure. The rates of decrease in sulfate and increase in alkalinity concentrations were complimentary and showed considerable linearity with time. When the pressure in the reactor was decreased below the methane hydrate stability field, following the methane hydrate dissociation, sulfate reduction abruptly decreased. When the pressure was restored all the reactions returned to their previous rates. Much of the methane oxidation activity in the reactor is believed to occur in association with the methane hydrate. Upon the completion of one of the experiments, the chamber methane hydrate, liquid phase, and sediment were separated. FISH analyses of the dissociated hydrate fluid indicate a significant presence of Archaea in or on the hydrate. The cell densities in the bioreactor medium liquid phase were 7.2 x 10$^{7}$ cells/cc, and with the methane hydrate, 2.8 x 10$^{8}$ cells/cc.
DE: 0330 Geochemical cycles
DE: 0400 Biogeosciences
DE: 4840 Microbiology
SC: Biogeosciences [B]
MN: 2003 Fall Meeting