Paleoclimate-induced stress on polar forested ecosystems prior to the permian-triassic mass extinction

The end Permian extinction was the most severe mass extinction in the history of metazoan life on Earth. However, re-examined floristic records and new radiometric ages from Gondwanan successions suggest a nuanced terrestrial ecosystem response to end Permian global change. Thus, the timing of terrestrial ecosystem change may be significantly older than the well-dated marine record of the end Permian extinction; and the magnitude of the response to the end Permian was variable among terrestrial taxa. Furthermore, paleosol records and paleoclimate simulations from eastern Australia suggest climate change as a principal driver, with a lowering of hemispheric temperature gradients affecting paleo high-latitude ecosystems during the Late Permian. To evaluate the climate response of plant communities to the end Permian extinction this study focuses on applying the technique of dendrochronology to produce annual-resolution records of tree ring growth for a succession of Late Permian fossil forests and early Middle Triassic fossil forests from Antarctica. These decade to multi-centennial scale records of climate change are compared against long-term averages of paleoclimate derived from paleosol proxies. The dendrochronologic results and paleosol-based paleoclimate results are compared across space during the Late Permian and through time. The results of these paleoclimate proxies indicate that long-term averages of paleoclimate become more similar at two locations separated by ~9º latitude during the Late Permian, and paleoclimate at these locations was identical by the early Middle Triassic. The annually-resolved plant response to paleoclimate reveals a complementary trend, however, latest Permian dendrochronologic results are nearly identical to the early Middle Triassic with the exception that marked years of limited wood growth during the Late Permian occur on similar frequencies as average to enhanced growth during the early Middle Triassic. These results suggest that paleoclimate change during the Late Permian exerted significant stress on high-latitude forests, consistent with the hypothesis developed for eastern Australia, and was likely the primary driver of the extinction of the glossopterid ecosystems.