Indian summer monsoon variations since late MIS3: A perspective from multiproxy evidence from Lake Xingyun in southwestern China

The variability of the Indian summer monsoon (ISM) is a central research topic tightly linked to precipitation changes in the highly populated South Asian monsoon region. Understanding the variability and related dynamic mechanisms of the ISM on orbital-millennial time scale provides insight into the metastable nature of the Earth's system, which offers favorable conditions for disaster prevention and mitigation. Here, we present a multiproxy record spanning the late Marine Isotope Stage 3 (40.2–0.0 cal ka BP), including median grain size, n-alkane distribution pattern, hydrogen isotope of C₃₁ n-alkane (δD_C31), and stable oxygen isotope of endogenic carbonates (δ¹⁸O_carb) from Lake Xingyun in southwestern China. The results showed that the ISM relatively strong during 40.2–30.0 cal ka BP, weakened during 30.0–16.0 cal ka BP and then it was progressively enhanced during 16.0–11.7 cal ka BP. The strongest ISM occurred during 10.7–6.5 cal ka BP and became weakened during 6.5–0.0 cal ka BP. The ISM precipitation increased overall with rising temperatures on the orbital scale despite of some millennial exceptions. The ISM variations were strongly controlled by changes in Northern Hemisphere summer insolation, and influenced by Earth's boundary conditions (i.e., CO₂ concentration and ice sheets) during the glacial-interglacial period. Moreover, the Heinrich Events (i.e., H3, H2, and H1) and Younger Dryas (YD) occurred in different climatic states of the Earth system, and thus the ISM responded differently in magnitude to these millennial-scale cold events. As such, the ISM during Heinrich Events (i.e., H3, H2, and H1) was more significantly weakened than that during the YD. These findings highlight the complexity of ISM changes with different warming scenarios, and provide a perspective for understanding the different hydrological responses to abrupt cold events in terms of magnitude.