Spatiotemporal variations of chemical weathering intensity in large drainage basin and its potential climatic implications: A case study from the Yangtze River Valley.

The knowledge on continental chemical weathering has a role in understanding carbon cycle and climate change. However, regional-scale spatiotemporal analysis of chemical weathering in large drainage basins is relatively seldom performed. In this study, based on 718 A- and C-horizon soil samples, we examined the spatiotemporal variations of chemical weathering intensity (i.e., the Chemical Index of Alteration (CIA)) in the Yangtze River Valley (YRV) by using trend surface analysis (TSA) and spatial correlation analysis (SCA). We found that: (1) the average CIA values of 68.4 and 68.5 for the A- and C-horizon soils reflect an overall intermediate chemical weathering in the YRV; (2) the weathering intensities follow a latitudinal distribution pattern that they increased from 50 to 70 in the north/northwest to 70–90 in the south/southeast of the YRV; (3) the general trend of chemical weathering is preferential leaching of Ca and Na over K; (4) TSA and SCA suggest a relatively dominant control of precipitation on the weathering intensity than temperature; (5) regions with frequent, long-duration and intense heavy precipitation (≥5 days/y and daily rainfall ≥50 mm) and heatwave (≥2 times/y, ≥15 days per time, and ≥ 40 °C) are featured with anomalous silicate weathering whose intensity was diminished from C- to A-horizon; and (6) the absolute differences of the mean CIA values between C- and A-horizon whether in the YRV or sub-regions were <1, indicating a stable silicate weathering. We conclude that significant latitude effect embodies the dominant control of monsoon climate on the chemical weathering in the YRV. Local climate extremes (e.g., rainstorms) are accompanied by anomalous silicate weathering. However, decreasing weathering intensity from bottom up does not necessarily indicate alleviated climate extremes, but probably the loss of terrestrial carbon stocks. • Spatiotemporal variations of weathering intensity in the Yangtze valley were examined. • Trend surface analysis and spatial correlation analysis were performed. • Monsoon climate controls the latitudinal distribution pattern of weathering intensity. • Climate extremes create anomalous silicate weathering but decrease the intensity. [ABSTRACT FROM AUTHOR]