Sulfide oxidation affects the preservation of sulfur isotope signals

• Published in: Geology (Boulder) 2019-08, Vol.47 (8), p.739-743
• Main Authors: Findlay, Alyssa J, Boyko, Valeria, Pellerin, André, Avetisyan, Khoren, Guo Qingjun, Guo Qingjun, Yang Xi, Yang Xi, Kamyshny, Alexey
• Format: Article
• Language: English
• Subjects: Aha Reservoir; Archean; Asia; Biogeochemistry; Biological activity; chemical fractionation; Chemical reactions; China; Cycles; Earth; Earth atmosphere; Evolution; Far East; geochemical cycle; geochemistry; Geology; Guizhou China; hydrochemistry; isotope ratios; Isotopes; lacustrine environment; lake sediments; Lakes; Microorganisms; Minerals; modern analogs; Neoarchean; Oceans; Organic chemistry; Oxidation; Oxygen; Planetary evolution; Precambrian; Preservation; pyrite; Reduction; S-34/S-32; Sediments; stable isotopes; sulfate ion; Sulfate reduction; Sulfates; Sulfides; Sulfur; sulfur cycle; Sulfur isotopes; Sulphate reduction; Sulphides; Sulphur; Water circulation; Water column
• ISSN: 0091-7613; 1943-2682
• DOI: 10.1130/G46153.1

The accumulation of oxygen in Earth's atmosphere and oceans in the late Archean had profound implications for the planet's biogeochemical evolution. Oxygen impacts sulfur cycling through the oxidation of sulfide minerals and the production of sulfate for microbial sulfate reduction (MSR). The isotopic signature of sulfur species preserved in the geologic record is affected by the prevailing biological and chemical processes and can therefore be used to constrain past oxygen and sulfate concentrations. Here, in a study of a late Archean analogue, we find that the sulfur isotopic signature in the water column of a seasonally stratified lake in southern China is influenced by MSR, whereas model results indicate that the isotopic signature of the underlying sediments can be best explained by concurrent sulfate reduction and sulfide oxidation. These data demonstrate that small apparent sulfur isotope fractionations (#2d34Ssulfate-AVS = 4.2ppm-1.5ppm; AVS-acid volatile sulfides) can be caused by dynamic sulfur cycling at millimolar sulfate concentrations. This is in contrast to current interpretations of the isotopic record and indicates that small fractionations do not necessarily indicate very low sulfate or oxygen.