NICKEL ISOTOPES LINK SIBERIAN TRAPS AEROSOL PARTICLES TO THE END-PERMIAN MASS EXTINCTION (Invited Presentation)

Of the five major Phanerozoic extinctions, the end-Permian was most severe. Siberian Traps volcanism is considered the leading cause, having produced enormous volumes of magma and associated volatiles starting ~300 kyr prior to the extinction. But how, specifically, did flood basalt eruptions lead to widespread extinction? Proposed kill mechanisms include global warming, UV exposure, ocean acidification, marine anoxia, and even mercury poisoning. Two recent discoveries have also pointed to magma-derived nickel as a potential factor: first, a mechanism by which aerosol particles traveling from eruption sites to the oceans could have carried Ni from magmatic sulfide droplets [1], and, second, a spike in marine sediment Ni concentrations concomitant with extreme perturbation of the C cycle at the start of the event [2]. Increased Ni in the oceans would have greatly stimulated methanogens, for whom Ni is often a limiting nutrient [3]. Enhanced abundance of this nutrient, as well as evolution of metabolically efficient methanogens just at this time [2], likely led to a surge in CH4 production. This can explain the gradual and then sharply worsening anoxia evident in the rock record. Using Ni stable isotopes, we present direct evidence that Ni in marine sediments just below the extinction horizon indeed originated in magmatic sulfide droplets [4]. While black shales and nearly all other sedimentary rocks have relatively heavy Ni isotopic compositions (δ60Ni = -0.2 to +2.4‰), black shales below the extinction horizon in the Buchanan Lake section of the Sverdrup Basin, Arctic Canada, are exceptionally light (-1.1 to +0.35‰). The only known explanation for such light isotopic compositions is incorporation of Ni from sulfides. The Sverdrup Basin was directly downwind from the Siberian Traps in Late Permian time and records other evidence of Siberian Traps input, including coal ash [5]. We conclude that Ni carried on aerosol particles contributed directly to degradation of the marine environment and ultimately to the demise of most life forms 251 million years ago.

[1] Le Vaillant et al. (2017) doi: 10.1073/pnas.1611086114; [2] Rothman et al. (2014) doi: 10.1073/pnas.1318106111; [3] Diekert et al. (1981), J Bacteriol, 148:459; [4] Li et al. (2021) doi: 10.1038/s41467-021-22066-7; [5] Grasby et al. (2011) doi.org/10.1038/ngeo1069