Sulphur and carbon isotopes as tracers of past sub-seafloor microbial activity

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  • Patrick Meister, University of Vienna, Microsensor Group
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  • Benjamin Brunner, Department of Geological Sciences, University of Texas at El Paso, Microsensor Group
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  • Aude Picard, University of Nevada Las Vegas, Microsensor Group
  • ,
  • Michael E. Böttcher, Leibniz Institute for Baltic Sea Research Warnemünde
  • ,
  • Bo Barker Jørgensen

Microbial life below the seafloor has changed over geological time, but these changes are often not obvious, as they are not recorded in the sediment. Sulphur (S) isotope values in pyrite extracted from a Plio- to Holocene sequence of the Peru Margin (Ocean Drilling Program, ODP, Site 1229) show a down-core pattern that correlates with the pattern of carbon (C) isotopes in diagenetic dolomite. Early formation of the pyrite is indicated by the mineralogical composition of iron, showing a high degree of pyritization throughout the sedimentary sequence. Hence, the S-record could not have been substantially overprinted by later pyrite formation. The S- and C-isotope profiles show, thus, evidence for two episodes of enhanced microbial methane production with a very shallow sulphate-methane transition zone. The events of high activity are correlated with zones of elevated organic C content in the stratigraphic sequence. Our results demonstrate how isotopic signatures preserved in diagenetic mineral phases provide information on changes of past biogeochemical activity in a dynamic sub-seafloor biosphere.

Original languageEnglish
Article number604
JournalScientific Reports
Number of pages9
Publication statusPublished - 2019

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