Multiple sulfur isotope fractionations in biological systems: A case study with sulfate reducers and sulfur disproportionators

Abstract

Multiple sulfur isotope measurements of sulfur compounds associated with dissimilatory sulfate reduction, elemental sulfur disproportionation and sulfite disproportionation indicate that different types of metabolic processes impart different multiple isotope signatures. An established network for sulfate reduction was used previously to explain the multiple isotope variability. Here, we revisit that treatment and expand it to branching networks representative of biological sulfur disproportionation, in an attempt to understand multiple sulfur isotope fractionations associated with that metabolism. We use this context to interpret experimental data for both sulfate reducers and sulfur compound disproportionators. We explore the types of information about material flow through these metabolic processes that can be extracted by using multiple sulfur isotope data. The different multiple sulfur isotope relationships (Δ³³S′ and λ) allow various metabolic processes to be distinguished from one another, even when δ³⁴S fractionations are similar, providing a tool that can be used to interpret and identify different types of biological sulfur fractionations in the geologic record.