C3/C4 vegetation dynamics and hydroclimate variations in South China over the last two glacial-interglacial cycles

The responses of climate and environment in the tropical-subtropical monsoon region of East Asia to both internal and external forcings remain poorly understood, largely due to the scarcity of high-resolution terrestrial records that span multiple glacial-interglacial cycles. In this study, we present an organic carbon isotope (δ¹³C_org) record from Tianyang maar lake in Guangdong Province, tropical South China, covering the past ∼250 kyr. This record reflects significant variations in the relative abundance of C₃ and C₄ biomass in the local terrestrial vegetation at orbital timescales, which we contend are primarily driven by changes in regional precipitation. Specifically, C₄ plants dominate in the drier climates of glacial periods, while C₃ plants thrive in the more humid conditions of interglacial periods. Superimposed on glacial-interglacial alternations, C₃/C₄ vegetation composition and associated precipitation exhibit high-frequency fluctuations, for which corresponding spectral analysis reveals prominent half-precession signals. This suggests a linkage between the ecosystem and hydroclimate dynamics in the study region and equatorial insolation at orbital timescales, with El Niño/Southern Oscillation (ENSO)-like variability possibly acting as a bridging mechanism. Our findings highlight the combined influence of glacial and low-latitude insolation forcings on terrestrial ecosystems and hydroclimate in tropical East Asia, thereby enhancing our understanding of the variability and forcing mechanisms of the East Asian Summer Monsoon (EASM) during the late Quaternary.