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Bo Barker Jørgensen

The multiple sulphur isotope fingerprint of a sub-seafloor oxidative sulphur cycle driven by iron

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  • Jiarui Liu, China University of Geosciences, Wuhan, Massachusetts Institute of Technology
  • ,
  • André Pellerin
  • Gareth Izon, Massachusetts Institute of Technology
  • ,
  • Jiasheng Wang, China University of Geosciences, Wuhan
  • ,
  • Gilad Antler, Department of Geological and Environmental Sciences, Ben-Gurion University of the Negev, The Interuniversity Institute for Marine Science Eilat
  • ,
  • Jinqiang Liang, Guangzhou Marine Geological Survey
  • ,
  • Pibo Su, Guangzhou Marine Geological Survey
  • ,
  • Bo Barker Jørgensen
  • Shuhei Ono, Massachusetts Institute of Technology

Oxidative sulphur cycling is pervasive in marine sediments, replenishing the oxidised sulphur reservoir via re-oxidation of sulphide. An active, yet cryptic, sulphur cycle has been proposed to operate at depth beneath the sulphate-methane transition (SMT), fuelled by simultaneous sulphide oxidation and sulphate reduction under low-sulphate conditions. The existence of a cryptic sulphur cycle, however, is centred on porewater and genetic data that have little, to no, preservation potential, and thus are rarely accessible from the geological record. The absence of a suitable archive has hindered our ability to reconstruct the operation and importance of the cryptic sulphur cycle through space and time. To overcome this obstacle, and to develop a better understanding of the oxidative sulphur cycle in the deep biosphere, we have determined the abundance and triple sulphur isotope composition (Δ33S and δ34S) of both elemental sulphur and pyrite extracted from sediments recovered from the methane prone Taixinan Basin, South China Sea. Here, multiple sulphur isotope systematics of pyrite clearly reveal a tiering, with organoclastic sulphate reduction succumbing to sulphate-driven anaerobic oxidation of methane at depth. Importantly, a negative Δ33S-δ34S correlation was found at the periphery of the SMT that requires repeated and sustained iron-driven sulphide oxidation with concomitant disproportionation of the elemental sulphur product. We conclude that minor sulphur isotopes may provide a unique lens to resolve the cryptic sulphur cycle, allowing the importance of the deep biosphere to be evaluated over geological timescales. In turn, a better understanding of the cryptic sulphur cycle remains central to testing hypotheses linking major elemental cycles and diverse microbial activities that persist under the energy-limited conditions that typify the deep biosphere.

Original languageEnglish
Article number116165
JournalEarth and Planetary Science Letters
Number of pages10
Publication statusPublished - 2020

    Research areas

  • cryptic sulphur cycle, deep biosphere, sedimentary pyrite, South China Sea, sulphur disproportionation, triple sulphur isotopes

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