TY - JOUR
T1 - Oxygen isotope biogeochemistry of pore water sulfate in the deep biosphere
T2 - Dominance of isotope exchange reactions with ambient water during microbial sulfate reduction (ODP Site 1130)
AU - Wortmann, Ulrich G.
AU - Chernyavsky, Boris
AU - Bernasconi, Stefano M.
AU - Brunner, Benjamin
AU - Böttcher, Michael E.
AU - Swart, Peter K.
N1 - Funding Information:
Discussions with Laura Lee and James Walker, and the comments of three anonymous reviewers helped to focus our ideas. M.E.B. thanks S. Lilienthal and the Max Planck Society for support. U.G.W. thanks the Natural Sciences and Engineering Research Council Canada NSERC, which supported this study, and the German Science Foundation DFG which supported his participation on ODP Leg 182. U.G.W. and P.K.S. thank crew, scientific party, and technicians of the JOIDES Resolution on ODP Leg 182 for their support and commitment which facilitated the recovery of these samples under difficult conditions. The authors thank B. Schnetger (ICBM Oldenburg) for XRF analyses and M.E.B. thanks A. Schipper for technical assistance.
PY - 2007/9/1
Y1 - 2007/9/1
N2 - Microbially mediated sulfate reduction affects the isotopic composition of dissolved and solid sulfur species in marine sediments. Experiments and field data show that the δ 18 OSO42 - composition is also modified in the presence of sulfate-reducing microorganisms. This has been attributed either to a kinetic isotope effect during the reduction of sulfate to sulfite, cell-internal exchange reactions between enzymatically-activated sulfate (APS), and/or sulfite with cytoplasmic water. The isotopic fingerprint of these processes may be further modified by the cell-external reoxidation of sulfide to elemental sulfur, and the subsequent disproportionation to sulfide and sulfate or by the oxidation of sulfite to sulfate. Here we report δ 18 OSO42 - values from interstitial water samples of ODP Leg 182 (Site 1130) and provide the mathematical framework to describe the oxygen isotope fractionation of sulfate during microbial sulfate reduction. We show that a purely kinetic model is unable to explain our δ 18 OSO42 - data, and that the data are well explained by a model using oxygen isotope exchange reactions. We propose that the oxygen isotope exchange occurs between APS and cytoplasmic water, and/or between sulfite and adenosine monophosphate (AMP) during APS formation. Model calculations show that cell external reoxidation of reduced sulfur species would require up to 3000 mol/m3 of an oxidant at ODP Site 1130, which is incompatible with the sediment geochemical data. In addition, we show that the volumetric fluxes required to explain the observed δ 18 OSO42 - data are on average 14 times higher than the volumetric sulfate reduction rates (SRR) obtained from inverse modeling of the porewater data. The ratio between the gross sulfate flux into the microbes and the net sulfate flux through the microbes is depth invariant, and independent of sulfide concentrations. This suggests that both fluxes are controlled by cell density and that cell-specific sulfate reduction rates remain constant with depth.
AB - Microbially mediated sulfate reduction affects the isotopic composition of dissolved and solid sulfur species in marine sediments. Experiments and field data show that the δ 18 OSO42 - composition is also modified in the presence of sulfate-reducing microorganisms. This has been attributed either to a kinetic isotope effect during the reduction of sulfate to sulfite, cell-internal exchange reactions between enzymatically-activated sulfate (APS), and/or sulfite with cytoplasmic water. The isotopic fingerprint of these processes may be further modified by the cell-external reoxidation of sulfide to elemental sulfur, and the subsequent disproportionation to sulfide and sulfate or by the oxidation of sulfite to sulfate. Here we report δ 18 OSO42 - values from interstitial water samples of ODP Leg 182 (Site 1130) and provide the mathematical framework to describe the oxygen isotope fractionation of sulfate during microbial sulfate reduction. We show that a purely kinetic model is unable to explain our δ 18 OSO42 - data, and that the data are well explained by a model using oxygen isotope exchange reactions. We propose that the oxygen isotope exchange occurs between APS and cytoplasmic water, and/or between sulfite and adenosine monophosphate (AMP) during APS formation. Model calculations show that cell external reoxidation of reduced sulfur species would require up to 3000 mol/m3 of an oxidant at ODP Site 1130, which is incompatible with the sediment geochemical data. In addition, we show that the volumetric fluxes required to explain the observed δ 18 OSO42 - data are on average 14 times higher than the volumetric sulfate reduction rates (SRR) obtained from inverse modeling of the porewater data. The ratio between the gross sulfate flux into the microbes and the net sulfate flux through the microbes is depth invariant, and independent of sulfide concentrations. This suggests that both fluxes are controlled by cell density and that cell-specific sulfate reduction rates remain constant with depth.
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U2 - 10.1016/j.gca.2007.06.033
DO - 10.1016/j.gca.2007.06.033
M3 - Article
AN - SCOPUS:34548180148
VL - 71
SP - 4221
EP - 4232
JO - Geochmica et Cosmochimica Acta
JF - Geochmica et Cosmochimica Acta
SN - 0016-7037
IS - 17
ER -