Hydrology controls sulfuric acid-mediated weathering in an orogenic regime of southwestern Taiwan.

Chemical weathering is a pivotal geochemical process that shapes the carbon cycling and climates in the critical zone. Among its critical drivers, river discharge holds a particular significance, especially in the orogenic landscapes. Here, we examined the impact of discharge on mineral weathering in southwestern (SW) Taiwan by analyzing river water chemistry across a wide discharge range. Current observations indicated that carbonate contributes significantly to total weathering (50-80 %), with sulfuric acid accounting for one-half to two-thirds of carbonate weathering. A statistically strong correlation between river discharge and sulfuric acid-mediated carbonate weathering was highlighted, while the silicate weathering remained constant. This relationship suggests an increased influx of fresh minerals, such as pyrite, into the weathering regime as water flow increases. Our model identifies a critical discharge threshold of 4.6 m s, determining whether mineral weathering acts as a net source or sink of CO. Consequently, mineral weathering in SW Taiwan acts as a net CO sink during dry periods but turns into a net source during wet periods. Through analyzing a decade of daily discharge data, we found mineral weathering in SW Taiwan is a net CO source, with a 2.6-fold increase in annual mean discharge causing a 3.8-fold increase in net CO flux. This pattern is likely to be applicable to other similar minerals containing mountain-building regions, highlighting the significant role of hydrology in determining weathering sources and their potential impact on the carbon cycle balance.