Monsoonal and westerly influences on interglacial calcite deposition and environmental conditions in southern Tibetan Plateau

Two atmospheric circulation systems, the mid-latitude Westerlies and the Indian summer monsoon (ISM), are key drivers of hydroclimate variability in the Tibetan Plateau (TP). However, the variability of the Westerlies and the ISM in the TP and their relationship remain unclear. Here, we present a new, precisely dated speleothem record from Pumu Cave in the southern TP, spanning the past 339,000 years. The Pumu δ¹⁸O record closely tracks Northern Hemisphere summer insolation (NHSI) and aligns with speleothem δ¹⁸O records from both the ISM and East Asian Summer Monsoon regimes. In comparison to previous studies, the Pumu δ¹⁸O record is primarily interpreted as a proxy indicating the ISM intensity. Furthermore, the orbital-scale variability in Pumu δ¹⁸O, δ¹³C, and trace element records reveals that the ISM intensity governs effective rainfall in the southern TP. Additionally, the Pumu speleothem growth occurred exclusively during warm, wet interglacial periods, while hiatuses persisted throughout cold, dry glacial periods. This pattern mirrors findings from Tianmen Cave, reinforcing the hypothesis that interglacial temperatures are a prerequisite for speleothem formation in the TP, with strong ISM precipitation, low ice volume and high CO₂ levels providing sufficient conditions. Besides, differences in growth periods and δ¹⁸O amplitudes are also observed between Pumu and Tianmen speleothems, which likely suggest variations in their moisture sources and duration of seasonal ground thaw in different parts of the TP. While the Westerlies-related moisture does not appear to change orbital phases of the δ¹⁸O variability in the TP, which follows the NHSI dominantly, it modulates the amplitude of δ¹⁸O fluctuations. Finally, the different roles of the ISM and Westerlies suggest that while the ISM controls the hydroclimate dynamic variability, environmental conditions in the southern TP appear to be also influenced by global ice volume and CO₂ levels, highlighting the complex interplay among these climatic forcings.