Exploring the feedbacks of vegetation and carbon cycle processes to climate changes under thermal events in Northeast China by reconstructing Eocene climate and atmospheric CO2 levels

Paleoclimate fluctuations recorded in lake sediments provide critical evidence for global carbon cycle disturbances. The Eocene epoch marks a pivotal period in Earth's transition to modern climate patterns and vegetation, offering insights into future global warming and ecological responses. Lacustrine deposits in Northeast China preserve important “deep-time” paleoclimatic information, providing a terrestrial perspective for studying Eocene climate change. This study reconstructed Eocene vegetation dynamics, climate parameters and CO₂ levels of the Yilan Basin in Northeast China through palynological analysis, the Coexistence Approach (CA) method, the Climate Amplitude Method (CAM) and δ¹³C_wood records. An Eocene climate evolution model for Northeast China was established, addressing climate sensitivity, oceanic-lacustrine thermal event correlations, vegetation responses, and post-thermal event climate regulation mechanisms against the backdrop of extreme hot-cold alternations during the Eocene. Our study fills the gap in understanding the Eocene climate of Heilongjiang Province. By comparing the Yilan Basin's climate reconstruction results with those from other regions, as well as CO₂ reconstruction data with global Eocene atmospheric CO₂ trends, we elucidated the climate evolution dynamics of Northeast China throughout the entire Eocene. The Yilan Basin featured a typical Ca (Humid subtropical) climate with significant seasonal variations, with a MAT of 11.6 ± 0.1–21.3 ± 0.6 °C and MAP of 652 ± 40–1823 ± 99 mm. Thermal events (ETM2, ETM3) and warmer intervals (EECO, MECO) triggered significant negative carbon isotope excursions, with these continental responses lagging behind their marine counterparts. Regional temperature and precipitation associated with thermal events increased notably, and vegetation and CO₂ feedbacks to thermal and cooling events during the Eocene were consistent and coordinated. In post-thermal event climate regulation, silicate weathering and organic carbon burial played crucial roles, exerting negative feedbacks on CO₂-driven warming.