Chemical Weathering Intensity as a Reliable Indicator for Southwest Summer Monsoon Reconstruction: Evidence From Clay Minerals of Qionghai Lake Sediments Since the Last Glacial Maximum

Studying the evolution history of the southwest summer monsoon (SSM) throughout geological time, particularly during its strongest period in the Holocene, can improve our understanding of its variation and driving mechanisms, and even help predict future climate changes, due to its significant social and economic implications. 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] obtained from Qionghai Lake sediments and examined its response to paleoclimate and SSM. Our findings indicate that the intensity of chemical weathering generally aligned with changes in paleoclimate, exhibiting strong chemical weathering intensity during warm and humid climate conditions. In addition, the intensity of chemical weathering basically tracks the evolution of the SSM since the LGM. Our results support the view that the highest SSM intensity occurred during the early-middle Holocene, followed by gradual weakening during the late Holocene, with Northern Hemisphere summer insolation being the primary driver of the SSM evolution. The variations of the SSM and the corresponding intensity of chemical weathering were also influenced by the cumulative effects of glacier boundary conditions, North Atlantic climate fluctuations, and Intertropical Convergence Zone migrations.