Purpose This study aims to clarify the previously overlooked carbon sink associated with carbonate and silicate mineral dissolution in riverine suspended sediments, using the Yangtze River Basin as a case study. The main objectives of this study are: (1) to quantify the carbon sink potential (CSP), capacity (CSC), and flux (CSF) of sediment dissolution in the Yangtze River; (2) to identify carbon sink influencing factors in the Yangtze River Basin; and (3) to assess the contributions of carbon sink functions by sediment dissolution to both local and global carbon cycles. Materials and methods Mineral and chemical compositions of suspended sediments from the Yangtze River were analyzed alongside climatic, topographic, erosion, and lithological data. A major-cation-based carbon sink model was developed and a correction index was applied to reduce systematic errors. The CSP, CSC, and CSF were quantified by the model, while key influencing factors were identified by statistical analyses. Results and discussion Calcium, magnesium, sodium, and potassium compositions in the sediment decreased along the mainstream of the Yangtze River by 62.56%, 15.09%, 11.54%, and 1.58%, respectively, confirming mineral dissolution processes and their associated carbon sink functions. The corrected CSC was 0.1215 t CO2 per ton of sediment, about 28% higher than uncorrected estimates. Among it, carbonates dominated (62.9%) over silicates (37.1%) while calcium minerals accounting for the majority (91.6%) of the total CSC of the Yangtze River. The CSF reached 1.74 Tg C yr(-)& sup1; (17.52% of the whole basin's rock weathering sink), and the extrapolated global flux was 71.47 Tg C yr(-)& sup1; (22.33% of worldwide rock weathering sink). For driving forces, calcium mineral CSP increased with erosion intensity, elevation drop, and carbonate content; sodium and magnesium with silicate rocks; and potassium with temperature and aridity index. Conclusions Suspended sediment dissolution played a significant role in the carbon cycling, contributing substantially to both regional and global carbon sinks. This study highlighted the necessity of incorporating sediment-derived carbon sinks into global carbon budgets and underscored their potential for climate change mitigation. These findings revealed a previously neglected pathway of carbon sequestration, and could improve the regional and global carbon sink estimations, and provide new directions for climate change mitigation research.