Primary data

Understanding the changes in the southwest summer monsoon (SSM) is of great social and economic significance to the areas affected by it. Studying the evolution of SSM cover the course of geological history can help us understand current monsoon changes and even predict future ones. Given that there is still debate about the period when the SSM was strongest during the Holocene, along with a lack of longer timescale studies of monsoon evolution, we still have a limited understanding of the variation of the SSM and the mechanism driving it. Here we reconstructed the history of chemical weathering intensity since the Last Glacial Maximum (LGM) based on clay mineral proxies ((illite/smectite)/(illite+chlorite) and illite crystallinity) retrieved from Qionghai Lake sediments and discussed its response to paleoclimate and SSM. Our results showed that the intensity of chemical weathering was roughly consistent with the change of paleoclimate, exhibiting high-intensity chemical weathering in warm and humid climate conditions. In addition, the intensity of chemical weathering generally tracked the evolution of SSM since the LGM. Our results support the view that the highest SSM intensity occurred in the early-middle Holocene, followed by gradual weakening in the middle-late Holocene. The evolution of SSM is primarily forced by the Northern Hemisphere summer insolation. The glacier boundary conditions, North Atlantic climate fluctuations, and ITCZ migrations also exerted cumulative influences on the variations of the SSM and the corresponding intensity of chemical weathering.