Seasonal CO fluxes from alpine river influenced by freeze-thaw in the Qinghai Lake basin, northeastern of the Qinghai-Tibet Plateau.

River CO emissions, which contribute 53 % of the basin's overall carbon emissions, are essential parts of the global and regional carbon cycles. Previous CO flux calculates are mostly based on single samples collected during ice-free periods; however, little is known about the effects of freeze-thaw cycles on the river CO flux (FCO) of inland rivers in alpine regions. Based on one year-round monthly continuous field sampling, we quantified the FCO and determined their driving factors in typical rivers during different freeze-thaw periods in the Qinghai Lake Basin (QLB) using the thin boundary layer model (TBL) and the path analysis method. The findings indicated that (1) the average FCO in the typical rivers was 184.98 ± 329.12 mmol/m/d, acting as a carbon source during different freeze-thaw periods, and showed a decreasing trend with completely thawed periods (CTP, 303.15 ± 376.56 mmol/m/d) > unstable freezing periods (UFP, 189.44 ± 344.08 mmol/m/d) > unstable thawing periods (UTP, 62.35 ± 266.71 mmol/m/d); (2) pH, surface water temperature (Tw) and total alkalinity (TA) were the dominant controlling factors during different freeze-thaw periods. Interestingly, they significantly affected FCO more before completely frozen than after frozen, with Tw and TA changing from having promoting effects to having limiting effects; (3) in addition, dissolved carbon components indirectly affected FCO primarily through the indirect effects of pH and Tw in the UTP; wind speed (U) directly promoted FCO in the CTP; and Ca and dissolved inorganic carbon (DIC) were susceptible to indirect effects, which promoted/limited the release of FCO in the UFP, respectively. Our results reveal the changes of FCO and the factors influencing it in inland rivers within alpine regions during different freeze-thaw periods, thereby offering valuable support for carbon emission-related studies in alpine regions.