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An enormous sulfur isotope excursion indicates marine anoxia during the end-Triassic mass extinction

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Science Advances  09 Sep 2020:
Vol. 6, no. 37, eabb6704
DOI: 10.1126/sciadv.abb6704
  • Fig. 1 Simplified paleogeographical map for Triassic-Jurassic transition showing localities for all three studied sections.

    This figure is modified after the work of Luo et al. (16). T-J, Triassic-Jurassic. Yellow filled triangles indicate the location of studied sections. The paleogeographical location and the extent of CAMP are based on the work of Marzoli et al. (42).

  • Fig. 2 δ34SCAS profiles from Late Triassic to Early Jurassic for the three studied sites of the Tethys and Panthalassa oceans.

    R., Rhaetian. The orange shadowed field indicates the extended extinction interval following the major mass extinction horizon. The light green field indicates a hiatus between Norian and Rhaetian at the BBR. Dark green bars represent the fossil occurrence ranges. See the Supplementary Materials for further stratigraphic details. Vertical dash lines indicate pre- or postexcursion average baseline values.

  • Fig. 3 Sulfur cycle box model outputs.

    (A and B) Increased in the pyrite burial rate under different values for the starting oceanic sulfate inventory, with tests of 1 mM (A) (yellow) and 0.33 mM (B) (red). For both scenarios, a step increase in pyrite burial is assumed to occur at t = 0 over a period of 50 ka, which represents the ETME. Both models assume the same increase in pyrite burial rates, which ranges from 2- to 10-fold to create the shaded area, with the centerline showing a fivefold increase. The best fit to the data occurs for marine sulfate concentration [SO4] = 0.33 mM (B). (C) Attempts to fit the δ34SCAS data by instead reducing the pyrite weathering rate to zero over the same 50-ka time frame. Here, regardless of [SO4], the shape of the curve cannot be fit. This is because creating the large excursion this way requires extremely low [SO4], and, in these circumstances, the system is quick to regain isotopic stability. (D to F) Repetition of these experiments with the addition of a change in the enrichment factor ΔS between oceanic sulfate and sedimentary pyrite and continuation to produce a better fit when [SO4] = 0.33 mM.

  • Fig. 4 Conceptual model of the methane-oxygen link under high and low sulfate conditions.

    (A) The fate of organic carbon in the modern high sulfate ocean: More organic carbon and methane are oxidized by sulfate with negligible benthic methane flux, which limits water column oxygen demand. (B) The effect of enhanced methanogenesis in a low sulfate setting: The proportion of organic carbon available for methane production is increased, sulfate-driven anaerobic AOM oxidation is suppressed, and methane production moves closer to the sediment surface producing a high benthic oxygen demand. Red arrows in (B) indicate acceleration of biogeochemical pathways relative to modern, whereas dotted black arrows indicate retardation. (C and D) The envisaged oxygen depletion responses of the ocean to the same CO2 forcing under high and low sulfate conditions. Sulfate is thought to be removed by evaporite deposition. Marine anoxia is exacerbated by the increased oxygen demand as net seafloor methane fluxes increase during warming. MG, methanogenesis. SMTZ, sulfate-methane transition zone.

Supplementary Materials

  • Supplementary Materials

    An enormous sulfur isotope excursion indicates marine anoxia during the end-Triassic mass extinction

    Tianchen He, Jacopo Dal Corso, Robert J. Newton, Paul B. Wignall, Benjamin J. W. Mills, Simona Todaro, Pietro Di Stefano, Emily C. Turner, Robert A. Jamieson, Vincenzo Randazzo, Manuel Rigo, Rosemary E. Jones, Alexander M. Dunhill

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    The PDF file includes:

    • Figs. S1 and S2
    • Tables S1 and S2
    • Legend for data file S1
    • References

    Other Supplementary Material for this manuscript includes the following:

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