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| Titel |
Sulfur isotope effects during sulfide oxidation to sulfate: model meets reality |
| VerfasserIn |
Zainab Abdulrahman Beiruti, Benjamin Brunner, Casey Hubert, Timothy Ferdelman |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250040635
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| Zusammenfassung |
| The combination of laboratory experiments and numerical models in the study of stable
sulfur isotope fractionation is a useful tool that contributes to a better understanding of sulfur
transformations in the environment. Because sulfur isotope fractionation during oxidative
sulfur cycling is expected to yield much smaller isotope fractionation than sulfate reduction,
sulfur isotope effects during sulfide oxidation have not received much attention. Nevertheless,
in situations where sulfide oxidation dominates over other sulfur transformations, the imprint
of these small isotope effects is preserved. These isotope imprints provide crucial
information about the biogeochemical conditions under which sulfide oxidation
occurred. Unlike sulfate reduction, where sulfur intermediates are hardly accumulated
and rarely released to the environment, sulfide oxidation to sulfate often involves
accumulation of intra- and extracellular elemental sulfur as an intermediate, which
may be accessed later for oxidation to sulfate by the same or different organisms.
The accumulation and consumption of a pool of elemental sulfur complicates the
interpretation of sulfur isotope effects during sulfide oxidation, as kinetic sulfur isotope
effects from oxidation of sulfide to elemental sulfur are superimposed by sulfur
isotope exchange between sulfide and elemental sulfur, a pool that is simultaneously
altered by isotope effects related to the oxidation of elemental sulfur to sulfate.
We derived a numerical isotope mass balance model that combines the rates for
sulfur isotope exchange between sulfide and elemental sulfur, oxidation of sulfide to
elemental sulfur and oxidation of elemental sulfur to sulfate with the respective isotope
effects. With this model, we can predict the evolution of the isotope composition of
sulfide, elemental sulfur, and sulfate during a sulfide oxidation experiment. Sensitivity
tests show that these isotope trends not only strongly depend on the size of isotope
fractionation, but also on the individual oxidation rates and their relative timing to each
other. Our model results are compared to existing data in the literature, and with
new laboratory experiments in which sulfide was oxidized to elemental sulfur and
sulfate by pure cultures of Sulfurimonas strain CVO grown under nitrate-reducing
conditions. |
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