Spatiotemporal heterogeneity of Pliocene hydroclimate change across the East Asian monsoon region

Abstract

The hydroclimate evolution of the East Asian summer monsoon (EASM) during the Pliocene warm period, not clearly understood presently, is insightful for predicting its trends in future global warming. Here, we present paired biomarker records from northern South China Sea (SCS) Pliocene sediments, reconstructing sea surface temperature (SST) via TEX₈₆ proxy and terrestrial humidity through leaf wax n-alkane distributions. These datasets are systematically compared with records from the southern SCS that is part of the modern Western Pacific Warm Pool (WPWP). Our analyses reveal that Pliocene TEX₈₆-based mean SSTs in the northern SCS, exceeding the modern WPWP SSTs, co-vary with those in the Eastern Tropical Pacific and show a variable SST difference from the central WPWP, suggesting dynamic changes of the WPWP. Terrestrial humidity reconstructions demonstrate a dry-wet-dry oscillation over South China and a clear N-S moisture seesaw pattern across the SCS that are in concert with changes in Pacific zonal and meridional SST gradients. Integrated with EASM records in North China, these findings delineate a persistent tripole precipitation mode spanning the EASM domain in the Pliocene. The existence of this tripole precipitation mode suggests that atmospheric circulation mechanisms governing modern EASM variability persist as fundamental regulators of hydroclimate even under the equable climate conditions of the Pliocene.