Atmospheric ozone destruction and the end-Permian crisis: Evidence from multiple sulfur isotopes

The end-Permian mass extinction (EPME) is considered the largest biotic crisis of the Phanerozoic. To explain the worldwide destruction and mutation of land plants, previous work has emphasized the role of enhanced UV irradiation linked to volcanism-induced disruption of the ozone shield. However, direct evidence for a link between volcanic SO2 emission and stratospheric ozone deterioration is missing. Previous bulk analysis (i.e., SF6 method) found no Mass-Independent Fractionation of sulfur isotopes (MIF-S, noted A33S). However, possible grain scale sulfur isotope anomaly can be easily overlooked during bulk analysis. To detect possible sulfur isotope anomaly in grain scale, we applied in-situ multiple sulfur isotope analysis of the sulfide using secondary ion mass spectrometry (SIMS). We found a marked positive shift (higher than +0.30%o and up to +0.94%o) just before the end-Permian extinction in the Meishan section. Modelling shows that these positive A33S anomalies cannot be explained by Mass Dependent Fractionation (MDF) processes alone, rather by UV-induced photolysis of volcanic SO2. The formation and preservation of MIF-S anomalies in the atmosphere and subsequent transport to the oceans require intense and prolonged irradiation of the Earth's surface with solar UV, thus fingerprinting severe disruption of the atmospheric ozone balance at the onset of Earth's largest mass extinction.