Trends of geochemical and climate proxies indicating Late Ordovician–Silurian conditions and their relationship to mass extinction pulses (horizontal bars marked LOME-1 and -2). (A) δ13C of carbonates, used with biostratigraphic markers to correlate records in time. Previously published records of δ238U (B) recording non-sulfidic anoxia; and δ34S of carbonates (C) comparing previously published work from other sites with new datasets generated in this study (green and orange dots/line). Summary of generalized changes in extent of global marine anoxia (D) and euxinia (E) inferred from these proxies. Rightmost panels show inferred average sea surface temperatures (SSTs) (F) and eustatic sea level (G) over this period. Data are taken from a number of sources; see paper for citations. Credit: Kozik et al., 2022, Figure 6
Source: AGU Advances
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.

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. [2021] 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. [2021]. Geochemical records reveal protracted and differential marine redox change associated with Late Ordovician climate and mass extinctions. AGU Advances, 2, e2021AV000563.

—Susan Trumbore, Editor in Chief, AGU Advances

Text © 2022. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.