Source: AGU Advances
The Late Ordovician (Hirnantian; 445 Ma) hosted the second-most severe mass extinction in Earth history, eliminating 85% of marine species between two pulses, and is the only major mass extinction associated with icehouse conditions. However, the exact causes of extinction, especially the potential role of marine oxygenation, remain uncertain. Kozik et al.  present paired iodine concentrations and sulfur isotope data to constrain both local and global marine oxygenation surrounding the extinction. Their results indicate that during the two extinction pulses, local shelf anoxia (I/Ca proxy) persisted against a backdrop of waning and then waxing global euxinia – anoxia plus sulfidic water columns – based on δ34S variations in carbonates. Using geochemical models, they find that the mass extinction is strongly associated with expansions of non-sulfidic anoxia on shelves combined with glacioeustatic sea-level change and climatic cooling. This study provides new details on paleoredox conditions for Late Ordovician oceans and places them into the context of coincident changes in climate, eustatic sea level, and the biosphere.
Citation: Kozik, N., Gill, B., Owens, J., Lyons, T. & Young, S. . Geochemical records reveal protracted and differential marine redox change associated with Late Ordovician climate and mass extinctions. AGU Advances, 2, e2021AV000563. https://doi.org/10.1029/2021AV000563
—Susan Trumbore, Editor in Chief, AGU Advances