Analysis of Sulfur Isotopes Along a Wide Sulfide Concentration Gradient
Abstract
In this study we investigate the influence of increasing sulfide concentrations on the fractionation of stable sulfur isotopes during microbial sulfate reduction. Sulfide concentrations range from 0.2 to 40~mM in batch culture experiments with the marine sulfate reducer Desulfobacter latus. We discuss δ34S ratios of dissolved sulfate from two independent batch culture experiments where the 2nd experimental set reaches maximum sulfide concentrations of 40~mM, twice the amount of the 1st set. Both data sets are interpreted using a Rayleigh type fractionation model. The model results show that an individual Rayleigh type interpretation of the two S-isotope data sets reveals two different enrichment factors. More importantly, only the Rayleigh model curve for Exp.~1 is able to match its corresponding data. In contrast, the Rayleigh model curve for Exp.~2, where higher sulfide concentrations were present, results in a distinct S-isotope offset to its experimental data. Therefore, we introduce a single step sulfate reduction model that allows for a sulfide-S reflux (reoxidation) into the sulfate pool, to interpret our experimental data. Our proposed model is able to explain both experimental data sets including the aforementioned offset. As a consequence of the new reflux model, the apparent enrichment factor is not constant, unlike a Rayleigh model derived enrichment factor.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2009
- Bibcode:
- 2009AGUSM.H11B..01E
- Keywords:
-
- 0448 Geomicrobiology;
- 0454 Isotopic composition and chemistry (1041;
- 4870);
- 0488 Sulfur cycling;
- 1050 Marine geochemistry (4835;
- 4845;
- 4850);
- 4805 Biogeochemical cycles;
- processes;
- and modeling (0412;
- 0414;
- 0793;
- 1615;
- 4912)