HR: 11:32h
AN: B22A-07    [Abstracts]
TI: Isotope Biogeochemistry of Sulfur in a Cold-Water Carbonate Mound (IODP Site 1317)
AU: * Ferdelman, T G
EM: tferdelm@mpi-bremen.de
AF: Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, Bremen, D-28359, Germany
AU: Boettcher, M E
EM: michael.boettcher@io-warnemuende.de
AF: Leibniz Institute for Baltic Sea Research, Warnemünde Germany, Seestrasse 15, Warnemuende, D-18119, Germany
AB: To establish a depositional model for cold-water carbonate mounds, Challenger Mound and adjacent continental slope sites were drilled during IODP Expedition 307 in May 2005. Although a role for methane seepage and subsequent anaerobic oxidation was discounted both as a hard-round substrate for mound initiation and as a principal source of carbonate within the mound succession, interstitial water profiles of sulfate, alkalinity, Mg, and Sr indicated a tight coupling between carbonate diagenesis and mircrobial sulfate reduction. The reaction of sulfide with siliciclastic iron-bearing minerals to form pyrite was proposed to account for enhanced diagenetic carbonate precipitation (Ferdelman et al., 2006; Proc. IODP, vol. 307; doi:10.2204/iodp.proc.307.2006). To characterize these geomicrobial sulfur transformations in the carbonate mound sediments, the inorganic and stable isotope geochemical compositions of pore water sulfate and solid phase reduced sulfur compounds were performed. Acid-volatile sulfur (AVS) and pyrite del 34S compositions were usually similar and exhibited an increasing trend of from -40 per mil near surface to -20 per mil at the mound base at 132 mbsf. However, several excursions to more 34S sulfur enriched pyrite to values >0 per mil were observed in the deeper sections of the mound sequence. These excursions may be linked transitory changes in the depth of the methane-sulfate transition zone during mound build-up. The oxygen isotopic composition of residual dissolved sulfate indicates intracellular isotope exchange processes within the cells of SRBs, leading to increasing equilibration between extracellular pore water and sulfate.
UR: http://www.iodp.org
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0463 Microbe/mineral interactions
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 3036 Ocean drilling
DE: 4806 Carbon cycling (0428)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting