A Humid East Asia During the Early Pliocene Indicated by Calcite Nodules From the Chinese Loess Plateau

Understanding the monsoonal climate over East Asia during the warm Pliocene, the closest analog of the future warm climate, could better inform us of the regional hydrological responses to global climate change. However, the variations and controlling mechanisms of the regional hydrology during this warm period are not determined due to discrepancies among different proxy-derived records. Here we apply a multiproxy approach based on the geochemistry of calcite nodules from a Red Clay sequence located on the southern edge of the Chinese Loess Plateau. Both the trace metal/Ca ratios and the carbon and oxygen isotopic compositions of calcite nodules show low values during 5.4-4.1 Ma and increased during 4.1-3.3 Ma, together indicating a humid climate during the early Pliocene, the onset of drying starting at similar to 4.1 Ma and further intensification at 3.6 Ma. The timings of these hydrological transitions are consistent with global temperature changes, underlining the crucial role of meridional thermal gradient in shaping the regional hydroclimate over East Asia by modulating the strength and position of the East Asian summer monsoon. Plain Language Summary East Asia hosts one-third of the world's population. Understanding changes in the regional hydroclimate during the warm Pliocene, the nearest mid-twenty-first century climate analog in the geologic record, provides crucial knowledge for future sustainability. However, discrepancies exist among proxy-derived records, in part because few, if any, are controlled by hydroclimate only. Secondary carbonates in fossil soils are widely used to infer past hydrological changes. This study generates several records of regional hydrology based on the soil carbonate chemistry from the eolian deposits on the Chinese Loess Plateau. The results show that East Asia was wet during the early Pliocene (5.4-4.1 Ma) and became drier between 4.1 and 3.3 Ma. The timings of hydrological variations over East Asia coincide with global temperature changes, indicating the crucial role of Earth's thermal status through its control of regional wind systems.