Temporal evolution of glacial drainage system drives chemical weathering processes change during early ablation

• The selected polar glacier has a temporal stable supraglacial drainage system. • Subglacial channels under the temperate glacier reopened during early ablation. • Chemical weathering processes in polar glacier areas show minor seasonal change. • Sulfide oxidation becomes more active when subglacial channels reopen. • Net CO 2 consumption rate is regulated by seasonal change in glacial drainage system. The glacial environment is crucial to the global carbon cycle, as increased runoff and abundant fresh minerals enhance chemical weathering and promote carbon sink effects. However, the influence of temporal evolution in glacial drainage systems on chemical weathering processes and carbon sink effects remains poorly understood on the Tibetan Plateau, which hosts the densest glacier distribution in mid-to-low latitudes. This study examined two contrasting glacial catchments on the Tibetan Plateau: Rinong Qu, draining temperate glaciers, and Kuoqiong Qu, draining polar glaciers. The hydrochemistry of the river water in both catchments was analyzed during the initial ablation period (May to July) when air temperature rose significantly. Molar ratios of Ca 2+* /H 4 SiO 4 *, combined with tracer tests, revealed that the polar glacier was predominantly influenced by a stable supraglacial drainage system with minimal temporal change. In contrast, the temperate glacier was primarily characterized by a subglacial drainage system, evolving from a closed state to the reopening of subglacial channels after May 16. Budgets of major cations and dissolved inorganic carbon reveal that chemical weathering processes within the polar glacial catchment show minor temporal changes, despite water discharge increasing 13-fold. Conversely, the temperate glacial catchment experienced a 24 % decrease in carbonate dissolution and a 23 % increase in sulfide oxidation. More DIC originating from the atmospheric CO 2 was found when subglacial channels reopened (10 %). The net CO 2 consumption rate caused by chemical weathering (ФCO 2 _net) correlates positively with runoff and physical erosion rate in the polar glacial catchment but shows weak correlations in the temperate glacial catchment. ФCO 2 _net during the early phase of subglacial channels reopening period is ∼30 % lower than during the frozen period, despite water discharge and physical erosion rates being 2.4–4.4 times higher in the former. Overall, this study highlights that the temporal evolution of glacial drainage systems exerts an important influence on the carbon cycle by regulating chemical weathering processes.