Rapid marine oxygen variability: Driver of the Late Ordovician mass extinction

Abstract

The timing and connections between global cooling, marine redox conditions, and biotic turnover are underconstrained for the Late Ordovician. The second most severe mass extinction occurred at the end of the Ordovician period, resulting in ~85% loss of marine species between two extinction pulses. As the only “Big 5” extinction that occurred during icehouse conditions, this interval is an important modern analog to constrain environmental feedbacks. We present a previously unexplored thallium isotope records from two paleobasins that record global marine redox conditions and document two distinct and rapid excursions suggesting vacillating (de)oxygenation. The strong temporal link between these perturbations and extinctions highlights the possibility that dynamic marine oxygen fluctuations, rather than persistent, stable global anoxia, played a major role in driving the extinction. This evidence for rapid oxygen changes leading to mass extinction has important implications for modern deoxygenation and biodiversity declines.

Protracted oxygenation across the Cambrian–Ordovician transition: A key initiator of the Great Ordovician Biodiversification Event?

“…These changes in our geochemical records may indicate a global decrease in marine reducing conditions, as latest Cambrian oceans potentially increased their capacity to bury additional Mn‐oxides, as well as increased the marine inventory of vanadium. While a contraction in reducing conditions may seem counter intuitive with respect to stressors of marine biota, brief oxygenation events associated with other major mass extinctions have been documented in ε 205 Tl auth records(i.e., Kozik et al, 2022; Newby et al, 2021). Brief oxygenation events like the one identified here, and in the latest Ordovician and end Permian, may have provided an additional stressor to faunas adapted to low oxygen conditions.…”