Modern Silicate Weathering Regimes Across China Revealed by Geochemical Records from Surface Soils

Knowledge of modern kinetically limited (i.e., silicate weathering depends on temperature and precipitation) and supply-limited (i.e., weathering is limited mainly by the supply of fresh material) weathering regimes is important for analyzing the weathering-CO2-climate system on geological timescales. However, on the global scale, there are large knowledge gaps in modern silicate weathering regimes and their possible shifts, due to the lack of spatial information on in situ weathering processes. Here, we present the first detailed compilation of the major element concentrations in bulk and fine fraction (<2 mu m) samples of surface soils from across China, which we use to investigate modern silicate weathering regimes across China and possible shifts between regimes induced by tectonic uplift and climate changes. The results show that changes in climatic factors, especially precipitation, exert a first-order control on spatial variations in silicate weathering intensity (expressed by the chemical index of alteration, CIA), with additional contributions from nonclimatic factors. Comparison of silicate weathering regimes with the CIA suggests that for bulk samples the supply-limited weathering regime prevails in areas with CIA > 80, and the kinetically limited regime prevails in areas with CIA < 80. A significant inference from the results is that tectonic uplift and global warming could cause shifts between supply-limited and kinetically limited weathering regimes in the active mountain belts and floodplains of southern China and in areas dominated by intermediate chemical weathering. However, no shifts would occur in some of the arid to extremely arid areas of northern China and in highland areas with extreme chemical weathering.