HR: 16:45h
AN: B42E-04    [PDF]
TI: Sulfur Isotopic Analysis of Water and Sediment From Lake Hoare, Antarctica
AU: * Anglen, B L
EM: banglen@indiana.edu
AF: Department of Geological Sciences, Indiana University, 1001 East 10th Street, Bloomington, IN 47405 United States
AU: Pratt, L M
EM: prattl@indiana.edu
AF: Department of Geological Sciences, Indiana University, 1001 East 10th Street, Bloomington, IN 47405 United States
AU: Bishop, J L
EM: jbishop@mail.arc.nasa.gov
AF: SETI Institute/NASA-Ames Research Center, Mail Stop 239-4, Moffett Field, CA 94035 United States
AU: Doran, P T
EM: pdoran@uic.edu
AF: Earth & Environmental Sciences, University of Illinois at Chicago, 845 West Taylor Street, Chicago, IL 60607 United States
AB: Lake Hoare is a perennially ice-covered lake located in the McMurdo Dry Valleys of east Antarctica. Benthic microbial mats containing sulfate reducing and sulfide oxidizing bacteria are present in anoxic waters at depths greater than 27 m. Extreme cold and dry conditions in the valleys make them compelling analogs for possible paleolake systems on Mars. Sediment samples from 9 to 39 cm core depth were taken from cores collected from the anoxic zone. Water column samples from 6 to 22 m depth were analyzed for sulfate content. Sulfur isotopic values ($\delta$$^{34}$S) were determined for sequentially extracted sulfur species in sediment and for sulfate precipitated from the water samples. Sulfur fractions recovered from water samples show $\delta$$^{34}$S values of about 14 per mil. Sulfate recovered from sediments show sulfate $\delta$$^{34}$S values ranging from -1 to -19 per mil and pyrite $\delta$$^{34}$S values ranging from -2 to -22 per mil. Sulfate and pyrite $\delta$34S values show synchronous shifts with depth. Sulfate $\delta$$^{34}$S values exhibit a positive offset of about 5 per mil from pyrite $\delta$$^{34}$S. Given concentrations of sulfate mostly less than 1mM in Lake Hoare and the $^{34}$S-enriched sulfate present in the water column, this small positive offset is inferred to reflect porewater sulfate present in the sediments combined with labile sulfides that were oxidized to sulfate in the lab. Upward decreasing values of $\delta$$^{34}$S for sediment pyrite combined with increasing pyrite contents near the sediment-water interface are consistent with enhanced bacterial sulfate reduction due to an expanding reservoir of anaerobic water within Lake Hoare.
DE: 1040 Isotopic composition/chemistry
DE: 1045 Low-temperature geochemistry
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting