PANGEAN SEASONALITY CHANGES ACROSS THE PERMIAN-TRIASSIC BOUNDARY INFERRED FROM CLIMATE MODELING IN CONJUNCTION WITH FOSSIL AND SEDIMENT DATA

The Permian-Triassic boundary (PTB,252Ma)is of interest because it encompasses severe geochemical, climate, and environmental changes that contributed to the extinction of morethan90%ofmarinespecies and70%ofterrestrialspecies. In particular, the massive eruption of the Siberian flood basalts and related processes coincide with a rise in temperature to a lethal hothouse climate, in particular in the tropics. The substantial climate change likely led not only to changes in the mean climate but also in climate variability. In this study, we assess the changes in seasonality across the Pangean continent inferred from sensitivity experiments with a comprehensive climate model in response to CO₂radiative forcing and cloud optical depth. The seasonality of the central Sydney Basin in southeastern Gondwana, as revealed from the climate simulations in agreement with geochemical and floral data, was characterized by dry warm summers and cold wet winters. The maximum modeled summer-to-winter temperature difference is about 21°C for the 4´the preindustrial atmospheric CO₂concentration, and 19°C for the 12.7´preindustrial CO₂concentration, potentially representing the transition from pre-PTB to PTB conditions. Under these simulations, proximity to the ocean led to high precipitation during the Gondwanan summer but markedly drier conditions during the Gondwanan winter. When considering a lower cloud optical depth parameterization in the 12.7´CO₂simulation, owing to biophysical-climate feedbacks in a higher CO₂world, average temperature increases but the seasonal temperature difference decreases to about 17°C. These modeling results are compared to seasonality changes in other locations of the Pangean continent. Changes in seasonality affect fluctuations in the correlation between diversity and locality of fossil data. These findings, together with climate-sensitive sediments, are used for biome reconstruction across the PTB.