<p>Identifying the missing carbon sink is a critical challenge in carbon cycle research. Carbonate weathering constitutes a potentially important mechanism for it. However, little has been reported about the carbonate weathering<b>-</b>related inorganic carbon sink fluxes (CCSF) in Huanglong Valley. Here, we collected water samples, measured hydrochemical parameters, calculated runoff depth and CCSF. Results showed that Ca²⁺ and HCO₃⁻ were the main ions. Piper and Gibbs diagrams indicated a HCO₃-Ca hydrochemical type controlled by rock weathering. The averages of (Ca²⁺ + Mg²⁺) to HCO₃⁻ and to (HCO₃⁻ + SO₄²⁻) were 0.65 and 0.59, with data points near the 1:2 line, suggesting ion origins from calcite and dolomite dissolution. This research focuses on a simplified computational methodology to improve CCSF assessment in alpine karst systems. We do not discuss potential HCO₃⁻ sources (e.g., deep-source CO₂, sulfuric/nitric acid-driven weathering, and silicate weathering), so our reported CCSF represents “apparent CCSF”, not the net atmospheric CO₂ sink. Besides, the spatial uniformity of runoff depth is a key simplifying assumption. The preliminary estimate of CCSF was 9.37 ± 8.74 tCO₂ km^− 2 a^− 1. Sensitivity analysis indicated that the temporal variation pattern of CCSF remains consistent across different runoff depths. Seasonal comparison implied that CCSF exhibits greater sensitivity to runoff depth than HCO₃⁻ does. A comparison with other catchments revealed that higher CCSF values correlate with higher runoff depth. The runoff depth may be the key driving factor governing CCSF. Our research improves the methodologies for assessing CCSF.</p>