Upper limits on the extent of seafloor anoxia during the PETM from uranium isotopes

Clarkson, Matthew O.; Lenton, Timothy M.; Andersen, Morten B.; Bagard, Marie-Laure; Dickson, Alexander J. and Vance, Derek (2021). Upper limits on the extent of seafloor anoxia during the PETM from uranium isotopes. Nature Communications, 12(1), article no. 399.

DOI: https://doi.org/10.1038/s41467-020-20486-5

Abstract

The Paleocene Eocene Thermal Maximum (PETM) represents a major carbon cycle and climate perturbation that was associated with ocean de-oxygenation, in a qualitatively similar manner to the more extensive Mesozoic Oceanic Anoxic Events. Although indicators of ocean de-oxygenation are common for the PETM, and linked to biotic turnover, the global extent and temporal progression of de-oxygenation is poorly constrained. Here we present carbonate associated uranium isotope data for the PETM. A lack of resolvable perturbation to the U-cycle during the event suggests a limited expansion of seafloor anoxia on a global scale. We use this result, in conjunction with a biogeochemical model, to set an upper limit on the extent of global seafloor de-oxygenation. The model suggests that the new U isotope data, whilst also being consistent with plausible carbon emission scenarios and observations of carbon cycle recovery, permit a maximum ~10-fold expansion of anoxia, covering <2% of seafloor area.

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