The impact of the Paleocene−Eocene Thermal Maximum on a lacustrine ecosystem in northeastern China: Perturbation and recovery

The Paleocene−Eocene Thermal Maximum (PETM) was a brief yet extreme warming event that profoundly affected marine ecosystems, whereas its impact on contemporaneous lacustrine systems remains less well constrained. This event highlights the fundamentally different responses of marine and terrestrial ecosystems to rapid perturbations in the carbon cycle. Here, we investigate a Paleogene lacustrine succession from the Bohai Bay Basin (BBB) in northeastern China, integrating high-resolution biogeochemical, cyclostratigraphic, and statistical analyses to reconstruct the coupled evolution of carbon-cycle perturbations, environmental change, and ecological turnover across the PETM. During the core-PETM interval, the BBB lacustrine system experienced rapid ecosystem expansion under warm, humid conditions, characterized by elevated primary productivity and enhanced organic carbon burial. This phase was marked by increased abundance of algae and aquatic macrophytes, accompanied by the development of hypoxic to anoxic conditions. In the subsequent recovery stage, sustained warming and increasing salinity likely restructured the ecological dynamics. The abundance of aquatic macrophytes and algae communities declined, whereas cyanobacteria progressively increased among primary producers. This ecological shift may have promoted localized increases in harmful algal taxa, intensified oxygen consumption, and consequently reduced biodiversity and destabilized the ecosystem. Following the core-PETM, the BBB lacustrine depositional environment gradually recovered. However, this post-crisis state did not simply return to pre-PETM conditions; cyanobacteria continued to increase, while algal diversity remained relatively low. These patterns suggest that the ecosystem established a new ecological equilibrium characterized by elevated primary productivity and enhanced organic matter preservation, but reduced ecosystem complexity. Our findings document the ecological succession of a continental lacustrine system under hyperwarming conditions, highlighting its nonlinear, phased response to climatic forcing. These results reveal complex feedbacks among climate change, hydrological processes, and ecosystem dynamics during the PETM and provide important insights into the potential responses of modern lacustrine systems to anthropogenic global warming, particularly in the context of increasing eutrophication and harmful algal blooms.