Abrupt collapse of a swamp ecosystem in northeast China during the Paleocene–Eocene Thermal Maximum

The Paleocene–Eocene Thermal Maximum (PETM, ~56 Ma) was a geologically abrupt and extreme global warming event that had a profound effect on global climate and ecosystems. Efforts to understand the response of vegetation to this hyperthermal event have hitherto primarily focused on Europe and North America. However, a limited record from China hampers the understanding of regional terrestrial ecosystem response to PETM warming. Here, we present the a detailed palynological record from the Fushun Basin, NE China, spanning the late Paleocene to early Eocene. The palynological assemblage reveals an abrupt change in vegetation composition as a response to PETM warming. Swamps dominated by taxodioid conifers (Cupressaceae) were abruptly replaced by communities of Pinaceae conifers and the megathermal genus Aquilapollenites. This marked the abrupt collapse of the swamp ecosystem during the PETM as climate became hotter and wetter and mean annual temperature (MAT) increased from 15.6 °C to 19.7 °C. Vegetation turnover was driven by rapid global warming and localised changes due to increases in precipitation, subsequent elevated water levels, and expansion of lake systems. The marked discrepancy in the characteristics and magnitudes of the respective vegetation responses shows that the effects of PETM warming were more severe for swamp ecosystems than for other terrestrial ecosystems. The PETM warming led to swamp degradation, frequent wildfires, and concomitant peat burning; these changes may have triggered further warming through positive feedback mechanisms.