HR: 0800h
AN: B21A-0860    [Abstracts]
TI: S and O Isotope Studies of Microbial S Cycling in the Deep Biosphere of Marine Sediments: Eastern Equatorial Pacific Ocean
AU: * Blake, R E
EM: ruth.blake@yale.edu
AF: Yale University, Geology and Geophysics, P.O. Box 208109, New Haven, CT 06520-8109 United States
AU: Bottcher, M E
EM: mboettch@mpi-bremen.de
AF: Department of Biogeochemistry, Max-Planck-Institute for Marine Microbiology, Celsiusstr, Bremen, D-28359 Germany
AU: Surkov, A V
EM: aleksandr.surkov@yale.edu
AF: Yale University, Geology and Geophysics, P.O. Box 208109, New Haven, CT 06520-8109 United States
AU: Ferdelman, T G
EM: mboettch@mpi-bremen.de
AF: Department of Biogeochemistry, Max-Planck-Institute for Marine Microbiology, Celsiusstr, Bremen, D-28359 Germany
AU: Jorgensen, B B
EM: mboettch@mpi-bremen.de
AF: Department of Biogeochemistry, Max-Planck-Institute for Marine Microbiology, Celsiusstr, Bremen, D-28359 Germany
AB: We have determined the oxygen ($^{18}$O/$^{16}$O) and sulfur ($^{34}$S/$^{32}$S) isotope ratios of porewater sulfate to depths of over 400 mbsf in sediments from open-ocean and upwelling sites in the Eastern Equatorial Pacific ocean. Sulfate $\delta$$^{18}$O ranges from near-normal seawater values (9.5 permil) at organic-poor open-ocean sites, to approximately 30 permil at sites with higher organic matter content and higher associated microbial activity. Depth-correlative trends of $\delta$$^{18}$O, $\delta$$^{34}$S, alkalinity, methane, ammonium and the presence of sulfide, indicate significant oxidation of sedimentary organic matter by sulfate-reducing microbial populations as well as anaerobic oxidation of methane. $\delta$$^{18}$O-SO$_{4}$ values at low-activity sites reveal the presence of significant microbial sulfur-cycling activity despite relatively flat sulfate concentration and $\delta$$^{34}$S profiles. This activity may include contributions from several processes including: enzyme-catalyzed equilibration between oxygen in sulfate and water superimposed upon microbial sulfate reduction, sulfide oxidation, and bacterial disproportionation of sulfur intermediates. Large isotope enrichment factors observed at low-activity sites (40-80 permil) likely reflect concurrent processes of: kinetic isotope fractionation, equilibrium fractionation between sulfate and water, and sulfide oxidation at low rates of sulfate reduction. Results of this study indicate that coupled measurements of S and O isotope ratios of porewater sulfate are a powerful tool for tracing microbial activity and sulfur cycling in marine sediments.
DE: 4805 Biogeochemical cycles (1615)
DE: 4840 Microbiology
DE: 4870 Stable isotopes
DE: 4800 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL
DE: 1050 Marine geochemistry (4835, 4850)
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting