Millennial-scale East Asian summer monsoon hydroclimate variability during 47–39 kyr B.P. inferred from a stalagmite IRMsoft-flux record in Southeastern China

Abstract

The East Asian Summer Monsoon (EASM) exhibited millennial-scale oscillations during the Last Glacial Period, characterized by alternating cold stadials and warm interstadials that were broadly synchronous with climate changes in the North Atlantic. However, the mechanism linking regional hydroclimate variability to high- and low-latitude forcing remains debated. Here, we present precisely dated speleothem multi-proxy records, including δ¹⁸O, δ¹³C, and an environmental magnetic proxy (IRM_soft-flux), spanning 46.92–39.18 kyr B.P. from Xianyun Cave, southeastern China. The IRM_soft-flux, serves as an indicator of precipitation intensity, revealing increases during Dansgaard-Oeschger (DO) events 12 and 11, consistent with enhanced water vapor influx into southern China. Maximum moisture availability occurred between 43.96 and 42.98 kyr B.P., encompassing the DO 11 event and a weak monsoon interval, as corroborated by concurrent δ¹³C depletion, enhanced growth rate, and high initial ²³⁴U/²³⁸U ratio. This period of increased hydrological activity coincides with the peak of the half-precession cycle, which influences the vertical temperature gradient in the equatorial western Pacific, as well as the minima of west-east sea surface temperature gradient (ΔSST) in the equatorial Pacific. During this El Niño-like state, a weakened East Asia Hadley circulation (EAHC) and a southward shift of the Western Pacific Subtropical High (WPSH) amplified moisture convergence over southern China. Our findings demonstrate that the thermocline variability in the tropical Pacific, propagated hydroclimatic signals to subtropical East Asia via ocean-atmosphere circulation coupling, particularly affecting regions near the water vapor source from tropical Pacific.