Evolution of silicate weathering in South China since 30 Ma: Controlling factors and global implications

Silicate weathering plays a significant role in regulating the carbon cycle and global climate by consuming atmospheric CO2 over geological timescales. However, the importance of this mechanism in relation to paleoclimate changes remains controversial. A major obstacle to progress is the lack of comprehensive and detailed silicate weathering records preceding the Neogene. Here, we present a long-term and continuous record of major and trace elemental compositions of clay-sized (<2 μm) siliciclastic sediment fractions from the International Ocean Discovery Program (IODP) Site U1501 in the northern South China Sea to reconstruct the evolutionary history of silicate weathering since 30 Ma and assess its links to tectonic/climate changes. The weathering proxies of the chemical index of alteration (CIA) and K/Al ratio indicate that the silicate weathering intensity of these sediments has had a decreasing trend over the past 30 Myr, which is coupled with paleoclimate proxies, deep-sea δ18O values and black carbon δ13C values, suggesting that global cooling and regional drying are the main driving factors for weathering intensity evolution. Furthermore, this study also provides reconstructions of the silicate weathering fluxes since the early Oligocene, highlighting that the CO2 consumption fluxes caused by silicate weathering have been mainly controlled by physical erosion fluxes rather than by chemical weathering intensity over geological timescales. Consequently, our findings indicate that with increased physical erosion flux and resultant elevated silicate weathering flux, carbon output modulates the carbon cycle, contributing to global cooling and ice sheet development through enhanced CO2 consumption.