Erosion modulates the effect of chemical weathering on atmospheric pCO2, Qinghai-Tibet Plateau

Abstract

Chemical weathering plays an important role in modulating Earth's climate. However, chemical weathering is usually influenced by multiple factors simultaneously (e.g., climate, topography and lithology), and it is difficult to understand how these variables modulate the effect of chemical weathering on atmospheric pCO₂. In this study, we collected and analyzed water chemistry and multiple isotopes (δ³⁴S_SO4, δ¹⁸O_SO4 and δ¹⁸O_H2O) in the Bailong River catchment to decipher how these variables influence chemical weathering and its effect on atmospheric pCO₂. We used the Monte Carlo inversion model to partition the sources of major cations and ${\mathrm{SO}}_4^{2-}$, and the results reveal that carbonate weathering is the dominant source contributing cations in river. Sulfide oxidation is the most important source for ${\mathrm{SO}}_4^{2-}$ and a supply-limited process that is highly dependent on slope. We thus think slope is main factor modulating the effect of chemical weathering on atmospheric pCO₂. Steep slope increases sulfide oxidation rate by elevating erosion, resulting in chemical weathering acting as a CO₂ source. In contrast, gentle slope could facilitate a thick regolith that contributes long-term silicate weathering and limits sulfide oxidation, resulting in chemical weathering acting as a CO₂ sink. And it has been found that the influence of temperature on chemical weathering becomes progressively pronounced with increasing altitude. This study investigated sulfide weathering in eroding Qinghai-Tibet Plateau, highlighting the geomorphologically controlled CO₂ effects of chemical weathering.