Sulphur Isotopes and Microbial Sulphur Cycling in Sediments

Abstract

The relative abundances of the main isotopes of sulfur (32S, 34S) in sediments are influenced only by kinetic fractionations, which principally occur during the the formation of H2S by microbial sulfate redn. The isotopic compn. of the H2S being produced at any instant varies with rates of oxidn. recycling of sulfate (which det. the max. fractionation) and rates of sulfate supply relative to rates of sulfate redn. (which det. the isotopic compn. of the sulfate being reduced). The isotopic compn. of seawater sulfate fluctuates over geol. time, consistent with variations in the amts. of sulfate removed to form pyrite by microbial sulfate redn. Analogous variations are seen in the compn. of marine pyrite through time. By contrast variations in the isotopic compn. of sulfate oxygen are affected by sulfate redn. and also by sulfide oxidn. (since oxygen can be supplied both from atm. O2 or water). Future research is likely to focus increasingly on the role of oxidn. processes in modifying sulfur isotope and sulfate oxygen isotope signatures. on SciFinder (R)