Astronomically paced carbon cycle changes in East Asia during the Early Eocene Climatic Optimum (EECO)

Understanding East Asian climate dynamics during the Early Eocene Climatic Optimum (EECO) may help to assess long-term regional climate responses to future global warming. However, the scarcity of long-duration and high-resolution carbon cycle records has hindered our understanding of East Asian climate variability during this interval. To help bridge this gap, we conduct a cyclostratigraphic analysis of organic carbon isotope (δ13Corg) variations from a 1009-m-thick fluviolacustrine succession in the Milai section of the Gonjo Basin, southeastern Tibet, establishing a precise astronomical time scale across the EECO (ca. 52.78–49.95 Ma). Our results demonstrate that orbital forcing dominated terrestrial carbon cycle fluctuations in the Gonjo Basin during the ca. 52.78–49.95 Ma interval. Eccentricity (405 kyr and ~100 kyr cycles) likely modulated precipitation patterns and oceanic ventilation, while obliquity (~173 kyr and ~50–38 kyr cycles) probably controlled high-latitude insolation as well as both equator-to-pole and cross-equatorial insolation gradients. These orbital mechanisms influenced the basin’s δ13Corg record by jointly controlling global carbon cycling. These findings provide new constraints on East Asian carbon cycle behavior and climatic responses during the EECO, potentially offering insights into future long-term regional climate trends under greenhouse conditions.