HR: 0800h
AN: B21D-0908    [Abstracts]
TI: Carbon Biogeochemistry of Marine Sediments at the ODP Leg 204, Hydrate Ridge
AU: * Li, Y
EM: li@srel.edu
AF: Savannah River Ecology Laboratory, Savannah River Site Drawer E, Bldg 737A, Aiken, SC 29802 United States
AU: Zhang, C L
EM: zhang@srel.edu
AF: Savannah River Ecology Laboratory, Savannah River Site Drawer E, Bldg 737A, Aiken, SC 29802 United States
AU: White, D C
AF: Center for Biomarker Analysis, University of Tennessee, Knoxville, TN 37932 United States
AU: Peacock, A
AF: Center for Biomarker Analysis, University of Tennessee, Knoxville, TN 37932 United States
AU: Romanek, C S
EM: romanek@srel.edu
AF: Savannah River Ecology Laboratory, Savannah River Site Drawer E, Bldg 737A, Aiken, SC 29802 United States
AU: Wang, Y
AF: Department of Geological Sciences, Brown University, Providence, RI 02912 United States
AU: Huang, Y
AF: Department of Geological Sciences, Brown University, Providence, RI 02912 United States
AU: Holland, M
EM: melanie.holland@asu.edu
AF: Department of Geological Sciences, Arizona State University, Tempe, AZ 85287 United States
AB: ODP Leg 204 was drilled on the Oregon continental margin to determine the distribution and concentration of gas hydrates in an accretionary ridge. The microbiological communities and biogeochemical properties of the hydrates are of special interest. Our goal was to study carbon biogeochemistry in the marine sediments collected from boreholes 1245B, 1245C, 1250D, 1244E and 1244F. The total organic carbon of all boreholes had a narrow range of \delta$^{13}$C values (-21.3 to -22.3\permil), indicating the predominance of a homogeneous source. Lipids were extracted from bulk sediment and separated into neutral-, glycol- and polar-fractions using silicic acid columns. The polar lipids were treated further for analyses of phospholipids fatty acids (PLFA) and compound-specific carbon isotope ratios. Total PLFA was low (less than 80 pmol/g) in boreholes 1245B and 1245C and generally decreased with depth. Total PLFA in borehole 1250D, however, increased with depth, ranging from 33 pmol/g at 30.24 mbsf (meters below seafloor) to 426 pmol/g at 134.7 mbsf. On the other hand, total PLFA in boreholes 1244E and 1244F were high (338.1 to 444.2 pmol/g) but without any obvious trends with depth. Overall, saturated fatty acids were predominant (less than 45% to 82%) in these borehole sediments and terminally branched fatty acids, indicative of sulfate-reducing bacteria, were up to 15% of total PLFA. In borehole 1250D, saturated fatty acids decreased from greater than 80% at the top of the core to less than 45% at depth. Meanwhile, the monounsaturated fatty acids increased from several percent to more than 20% with depth. The \delta$^{13}$C values of PLFA ranged from -45\permil to -50\permil, which were significantly lower than bulk organic carbon. It is unclear, however, whether these low values are attributed to the anaerobic oxidation of methane, which is known to occur in other gas hydrates of the Hydrate Ridge and Gulf of Mexico.
DE: 4806 Carbon cycling
DE: 4840 Microbiology
DE: 4870 Stable isotopes
DE: 4803 Bacteria
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting