Recurrent marine anoxia in the Paleo-Tethys linked to constriction of seaways during the Early Triassic

Recurrent global marine anoxia marked the Early Triassic in the aftermath of the Permian-Triassic mass extinction. Growing evidence suggests contrasting redox histories across regions, with differing durations and intensities of anoxic conditions, but proposed climate-induced mechanisms for marine anoxia cannot fully explain these contrasting redox histories. Here, we test the impacts of changes in continental configuration on the redox conditions during the Early Triassic. We combine redox proxy data and Earth system model simulations, together with geological evidence for continental configuration in the Paleo-Tethys, showing that regional differences in redox conditions developed in the Early Triassic, primarily as a consequence of restricted seaways. In the model, a reduction in the depth of the seaways connecting the Paleo-Tethys and Panthalassa oceans leads to deoxygenation of the seafloor in the restricted Paleo-Tethys, aligning with redox proxy data. Ocean deoxygenation in the Paleo-Tethys primarily arises from the weakening of regional ocean ventilation due to the disruption of deep-water flow across the seaways. In contrast, simulations show that changes in continental configuration prompted ocean ventilation and oxygenation in some regions of the Panthalassa and Neo-Tethys, which explains the earlier reoxygenation of these basins before the late Early Triassic, as indicated by redox proxies. These varying spatial patterns of the redox landscape throughout the Early to Middle Triassic may help account for the delayed recovery of marine taxonomic diversity until the Middle Triassic in the Paleo-Tethys, contrasting with the quicker recovery observed in other regions before the Middle Triassic.