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Selenium isotopes record extensive marine suboxia during the Great Oxidation Event

Kipp, Michael A. ; Stüeken, Eva E. ; Bekker, Andrey ; Buick, Roger

Proceedings of the National Academy of Sciences - PNAS, 2017-01, Vol.114 (5), p.875-880 [Periódico revisado por pares]

United States: National Academy of Sciences

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  • Título:
    Selenium isotopes record extensive marine suboxia during the Great Oxidation Event
  • Autor: Kipp, Michael A. ; Stüeken, Eva E. ; Bekker, Andrey ; Buick, Roger
  • Assuntos: Physical Sciences
  • É parte de: Proceedings of the National Academy of Sciences - PNAS, 2017-01, Vol.114 (5), p.875-880
  • Notas: ObjectType-Article-1
    SourceType-Scholarly Journals-1
    ObjectType-Feature-2
    content type line 23
    Author contributions: M.A.K., E.E.S., A.B., and R.B. designed research; M.A.K. and E.E.S. performed research; M.A.K. and E.E.S. analyzed data; and M.A.K., E.E.S., A.B., and R.B. wrote the paper.
    Edited by Mark H. Thiemens, University of California, San Diego, La Jolla, CA, and approved December 13, 2016 (received for review September 24, 2016)
  • Descrição: It has been proposed that an “oxygen overshoot” occurred during the early Paleoproterozoic Great Oxidation Event (GOE) in association with the extreme positive carbon isotopic excursion known as the Lomagundi Event. Moreover, it has also been suggested that environmental oxygen levels then crashed to very low levels during the subsequent extremely negative Shunga–Francevillian carbon isotopic anomaly. These redox fluctuations could have profoundly influenced the course of eukaryotic evolution, as eukaryotes have several metabolic processes that are obligately aerobic. Here we investigate the magnitude of these proposed oxygen perturbations using selenium (Se) geochemistry, which is sensitive to redox transitions across suboxic conditions. We find that δ82/78Se values in offshore shales show a positive excursion from 2.32 Ga until 2.1 Ga (mean +1.03 ± 0.67‰). Selenium abundances and Se/TOC (total organic carbon) ratios similarly show a peak during this interval. Together these data suggest that during the GOE there was pervasive suboxia in near-shore environments, allowing nonquantitative Se reduction to drive the residual Se oxyanions isotopically heavy. This implies O₂ levels of >0.4 μM in these settings. Unlike in the late Neoproterozoic and Phanerozoic, when negative δ82/78Se values are observed in offshore environments, only a single formation, evidently the shallowest, shows evidence of negative δ82/78Se. This suggests that there was no upwelling of Se oxyanions from an oxic deep-ocean reservoir, which is consistent with previous estimates that the deep ocean remained anoxic throughout the GOE. The abrupt decline in δ82/78Se and Se/TOC values during the subsequent Shunga–Francevillian anomaly indicates a widespread decrease in surface oxygenation.
  • Editor: United States: National Academy of Sciences
  • Idioma: Inglês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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