Inverse relationship between chemical weathering and monsoon intensity in the Northwestern South China Sea during the past 120 kyr

Silicate weathering is a critical component of the global carbon cycle over geological timescales. Marine sediments serve as key archives for reconstructing continental weathering histories; however， disentangling primary weathering signals from the effects of sea-level fluctuations remains a challenge. Here， we present a high-resolution geochemical record from core SYD2 on the northwestern shelf of the South China Sea （SCS）， spanning the last ～120 kyr. Provenance analysis indicates that the sediments are primarily derived from Hainan Island. We observe a strong positive correlation between the Chemical Index of Alteration （CIA） and Al/Si ratios， suggesting that the raw weathering signal is significantly biased by grain-size sorting modulated by sea-level changes. After correcting for this sorting effect， the adjusted CIA_c record exhibits a distinct anti-phase relationship with Asian Summer Monsoon intensity recorded by stalagmite δ¹⁸O from southern China. This suggests that intensified Asian Summer Monsoon precipitation enhanced physical erosion and shortened sediment residence time， thereby limiting the degree of chemical weathering. Spectral analysis reveals a dominant precession cycle in CIA_c， highlighting the regulation of low-latitude insolation on monsoon intensity and， consequently， the weathering regime in the northwestern SCS.