Chemical weathering in the Himalayan system in response to the evolution of the Indian summer monsoon since 37 ka

Clay minerals and Th-La elements indicate a mixture of sediments originating from the Ganges-Brahmaputra (G-B) Rivers, Indo-Burman ranges/Irrawaddy River and Godavari-Krishna (G-K) Rivers.

The Th-La quantitative reconstruction revealed that sediment supply from the G-B Rivers was reduced during a series of millennial-scale cold climate events (i.e., Younger Dryas and Heinrich Events) and the Last Glacial Maximum. By removing the control of sea-level factors on the percentage of clay minerals in the sediments, we suggest that the marked decrease in the illite chemistry index and the increase in the (illite+chlorite)/smectite ratio during cold climate periods reflect enhanced physical weathering and weakened chemical weathering in the Himalayan system.