HR: 10:20h
AN: B52A-01 INVITED    [Abstracts]
TI: Sulfur and oxygen isotope studies of sulfate reduction
AU: * Farquhar, J
EM: jfarquha@umd.edu
AF: University of Maryland, Essic and Geology, College Park, MD 20742,
AU: Canfield, D E
EM: DEC@biology.sdu.dk
AF: NordCEE and the Institute of Biology, University of Southern Denmark, Odense, D, Denmark
AU: Bao, H
EM: bao@lsu.edu
AF: Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803,
AU: Masterson, A
EM: delmaistro@gmail.com
AF: University of Maryland, Essic and Geology, College Park, MD 20742,
AU: Johnston, D T
EM: DTJ@oeb.harvard.edu
AF: Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138,
AU: Wing, B A
EM: wing@eps.mcgill.ca
AF: Earth and Planetary Sciences, McGill University, Quebec, QE H3A2A7, Canada
AB: I will discuss insights into sulfur and oxygen isotope fractionations of dissimilatory sulfate reduction and specifically insight provided by experiments with natural populations of sulfate-reducing bacteria from Faellestrand, Denmark. The experiments yielded relatively large magnitude sulfur isotope fractionations for dissimilatory sulfate reduction (up to approximately 45 ‰ for ³⁴S/³²S), with higher δ¹⁸O accompanying higher δ³⁴S, similar to that observed in previous studies. The seawater used in the experiments was spiked by addition of ¹⁷O-labelled water and the ¹⁷O content of residual sulfate was found to depend on the fraction of sulfate reduced in the experiments. The ¹⁷O data provides evidence for recycling of sulfur from metabolic intermediates and for an ¹⁸O/¹⁶O fractionation of ~25-30 ‰ for dissimilatory sulfate reduction, a magnitude that is consistent with isotopic exchange between a sulfite species and cell water. The molar ratio of oxygen exchange to sulfate reduction was found to be about 2.5. Using recent models of sulfur isotope fractionations we find that our combined sulfur and oxygen isotopic data places constraints on the proportion of sulfate recycled to the medium (78-96 %), the proportion of sulfur intermediate sulfite that was recycled by way of APS to sulfate and released back to the external sulfate pool (~70%) and also that a fraction of the sulfur intermediates between sulfite and sulfide were recycled to sulfate. These parameters can be constrained because of the independent information provided by δ¹⁸O, δ³⁴S, ¹⁷O labels, and Δ³³S.
DE: 0424 Biosignatures and proxies
DE: 0448 Geomicrobiology
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0488 Sulfur cycling
DE: 1041 Stable isotope geochemistry (0454, 4870)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting