Responses of the East Asian Summer Monsoon in the Low-Latitude South China Sea to High-Latitude Millennial-Scale Climatic Changes During the Last Glaciation: Evidence From a High-Resolution Clay Mineralogical Record

High-resolution clay mineral assemblage combined with Nd and Sr isotopic compositions of Core MD12-3434 located in the northern South China Sea was investigated to reveal terrigenous sediment response to the East Asian monsoon evolution during the last glaciation. Clay mineralogical variations indicate clear millennial-scale oscillations that are mainly due to rapid changes in the proportion of smectite to illite and chlorite. Smectite is derived predominantly from rapid chemical weathering of volcanic rocks in Luzon under strong summer monsoon, while illite and chlorite are mainly sourced from Taiwan through reinforced physical erosion. Thus, the smectite/(illite+chlorite) ratio is adopted to reconstruct the East Asian summer monsoon evolution during the last glaciation. Rapid increases in the smectite/(illite+chlorite) ratio imply strengthened summer monsoon occurred during Dansgaard-Oeschger and Bolling-Allerod interstadials. In contrast, rapid decreases in the ratio indicate relatively weakened summer monsoon happened during Heinrich and Younger Dryas stadials. These millennial-scale climatic signals documented by clay mineralogical compositions of deep-sea sediments in the South China Sea can be better preserved in calm deeper-water sedimentary environments. Our study highlights the prompt responses of the East Asian monsoon system to millennial-scale climatic changes occurred in high-latitude Northern Hemisphere through contemporaneous chemical weathering of volcanic rocks and/or sediment supply variations under strong physical erosion in the low-latitude South China Sea, implying an atmospheric teleconnection from the North Atlantic to the Asian monsoon region. Plain Language Summary This study presents the first deep-sea high-resolution clay mineralogical result to show the low-latitude East Asian monsoon system that actually responds to millennial-scale changes in high-latitude Northern Hemisphere. The mechanism is clay minerals as chemical weathering products on the Earth's surface to be contemporaneously affected from the global and regional climate changes. This study also indicates that millennial-scale climatic signals documented by clay minerals can be better preserved in deep and calm sedimentary environments to avoid interruptions of potential deep-sea sedimentary dynamic processes like contour currents.