The coupling between tectonic uplift and carbon cycling in collisional orogens is typically framed through silicate weathering−driven CO2 drawdown. However, the role of hydrothermal systems in modulating carbon budgets remains underexplored. We integrated hydrochemical and dual-carbon isotopic (δ13C, Δ14C) data from the Yarlung Tsangpo River(YTR) in Tibet and hot springs to quantify hydrothermal contributions to dissolved inorganic carbon (DIC) and CO2 degassing. Hydrothermal HCO3− accounts for 0%−30% of riverine DIC across the YTR system, showing a positive correlation (R2 = 0.62) with fault density. Fault-enhanced deep CO2 evasion from the YTR network was estimated at 8.4 × 109 mol/yr, offsetting 49.7% of the long-term CO2 drawdown by silicate weathering. The area-normalized deep CO2 evasion flux from surface waters (9.2 × 106 mol/km2/yr) is more than seven times higher than regional averages for solid Earth degassing in the Himalayan-Tibetan orogen, indicating that deep CO2 evasion from river systems constitutes 4%−11% of this regional degassing flux. When integrated with hydrothermal fluxes, chemical weathering in the YTR basin maintains a short-term net sink (−2.15 × 1010 mol/yr) but acts as a long-term net carbon source (+0.90 × 1010 mol/yr). Our findings challenge the paradigm of active tectonic regions serving as net carbon sinks, emphasizing rivers as critical, yet overlooked, conduits for deep carbon release.
Sun et al. (Thu,) studied this question.