Uranium isotope evidence for two episodes of deoxygenation during Oceanic Anoxic Event 2
Pogge von Strandmann, PAE
Proceedings of the National Academy of Sciences
National Academy of Sciences
Oceanic Anoxic Event 2 (OAE 2), occurring ∼94 million years ago, was one of the most extreme carbon cycle and climatic perturbations of the Phanerozoic Eon. It was typified by a rapid rise in atmospheric CO2, global warming, and marine anoxia, leading to the widespread devastation of marine ecosystems. However, the precise timing and extent to which oceanic anoxic conditions expanded during OAE 2 remains unresolved. We present a record of global ocean redox changes during OAE 2 using a combined geochemical and carbon cycle modeling approach. We utilize a continuous, high-resolution record of uranium isotopes in pelagic and platform carbonate sediments to quantify the global extent of seafloor anoxia during OAE 2. This dataset is then compared with a dynamic model of the coupled global carbon, phosphorus, and uranium cycles to test hypotheses for OAE 2 initiation. This unique approach highlights an intra-OAE complexity that has previously been underconstrained, characterized by two expansions of anoxia separated by an episode of globally significant reoxygenation coincident with the "Plenus Cold Event." Each anoxic expansion event was likely driven by rapid atmospheric CO2injections from multiphase Large Igneous Province activity.
For their contributions to this work, M.O.C., C.H.S., C.M.M., I.R.C., and H.C.J. were supported by the Royal Society of New Zealand, Marsden Fund Standard Grant UOO1314. T.M.L. was supported by the Natural Environment Research Council “Jurassic Earth System and Timescale” large grant and a Royal Society Wolfson Research Merit Award. P.A.E.P.v.S. was funded by European Research Council Consolidator Grant 682760 - CONTROLPASTCO2.
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