Eccentricity Forcing of the Hydrological Cycle in East Asia During the Early Eocene Climatic Optimum (EECO)

Abstract

The Early Eocene Climatic Optimum (EECO) may be a potentially useful analog for future global warming under high CO2 concentrations. However, a paucity of orbital-scale terrestrial records limits our understanding of how the hydrological cycle responded during this protracted (∼4 Myr) interval of global warmth. In this study, we combine zircon U-Pb dating and cyclostratigraphy to establish a high-resolution astronomical timescale spanning the EECO (∼52.9 Ma to ∼49.9 Ma) through a >1 km fluviolacustrine succession from the Gonjo Basin, Southeast Tibet. Our results suggest that hydroclimate variability in the region during this interval was strongly controlled by eccentricity forcing (∼405 Kyr, ∼135–100 Kyr, and possibly ∼200 Kyr cycles). The dominance of eccentricity forcing in our record is consistent with coeval marine records, and indicates that modulation of low-latitude summer insolation through nonlinear interactions with the global carbon cycle likely controlled hydroclimate and paleolake level in the Gonjo basin during the EECO. Our study offers new perspectives for the forcing mechanisms of terrestrial hydroclimate changes of East Asia in response to subtle changes in insolation during the EECO.