Freshwater ecosystem collapse and mass mortalities at the Paleocene-Eocene thermal maximum

The Paleocene-Eocene thermal maximum (PETM), an abrupt global warming event linked to massive injections of carbon into the ocean-atmosphere system, was associated with large-scale deep-sea benthic extinction and major changes in planktonic ecosystems. However, due to the paucity of well-preserved fossils and high-resolution paleoenvironmental records, the PETM impacts on terrestrial ecosystems remain unclear. Here, we present geochemical and biological records of a lacustrine PETM section with exquisite fossils preserved from the Jianghan Basin, eastern China. Our data reveal the temporal relationship between carbon cycle perturbation, environmental changes, and biotic responses. Paleotemperatures derived from carbonate clumped isotope indicate a rapid increase by ∼11 °C, synchronous with a negative carbon isotope excursion in organic matter and carbonates. Mass mortalities of terrestrial and aquatic animals were coincident with rapid warming during the PETM. Taphonomic features of animals, along with geochemical and sedimentological evidence, suggest that hyperthermal-induced toxigenic cyanobacterial blooms appear to be the most probable cause of the mass mortalities. Our findings expose a direct link between extreme warmth and increased probability of catastrophic ecological events in terrestrial ecosystems.