Mercury isotope evidence for marine photic zone euxinia across the end-Permian mass extinction

Marine photic zone euxinia was likely an important kill mechanism and obstacle to recovery during the end-Permian mass extinction alongside the dominant influence of volcanism, according to a global box model evaluated against mercury isotopes from the Meishan Section, China The driving forces, kill and recovery mechanisms for the end-Permian mass extinction (EPME), the largest Phanerozoic biological crisis, are under debate. Sedimentary records of mercury enrichment and mercury isotopes have suggested the impact of volcanism on the EPME, yet the causes of mercury enrichment and isotope variations remain controversial. Here, we model mercury isotope variations across the EPME to quantitatively assess the effects of volcanism, terrestrial erosion and photic zone euxinia (PZE, toxic, sulfide-rich conditions). Our numerical model shows that while large-scale volcanism remains the main driver of widespread mercury enrichment, the negative shifts of Delta Hg-199 isotope signature across the EPME cannot be fully explained by volcanism or terrestrial erosion as proposed before, but require additional fractionation by marine mercury photoreduction under enhanced PZE conditions. Thus our model provides further evidence for widespread and prolonged PZE as a key kill mechanism for both the EPME and the impeded recovery afterward.

Automated summary

According to the evaluation of mercury isotopes from the Meishan Section, China and a global box model, marine photic zone euxinia (PZE) with toxic, sulfide-rich conditions was likely an important kill mechanism and obstacle to recovery during the end-Permian mass extinction (EPME), alongside the dominant influence of volcanism. This model provides further evidence that PZE played a crucial role in both the EPME and the impeded recovery afterward.