Contemporary inorganic carbon fluxes from rapidly changing glacierized watersheds of the Himalaya

Abstract

Transport of Dissolved Inorganic Carbon (DIC) by glacier fed Himalayan streams links the atmospheric carbon dioxide (CO2) concentrations, glacial weathering, and the global carbon cycle. However, the importance of weathering-derived DIC fluxes through glacial streams of the Himalaya with concomitant short- and long-term variability in carbon cycle has rarely been examined. This study provides new constraints on the present day CO2 drawdown by chemical weathering and glacial streams DIC fluxes in the Himalaya. Consequently, we reassessed meltwater ionic composition of five glacierized basins in the central and the western Himalaya between the ablation seasons of 1989 to 2017. We demonstrate that the drawdown of CO2 through silicate weathering is ~2.9 × 105 mol km−2 yr−1 (~17%) for Na bearing minerals, ~3.8 × 105 mol km−2 yr−1 (~22%) for K bearing minerals, and 0.5 × 105 mol km−2 yr−1 (~3%) for Ca bearing minerals. Similarly, CO2 drawdown through carbonate weathering accounts for ~9 × 105 mol km−2 yr−1 (~58%) for Ca and Mg associated minerals (Ca-Mg carbonate). The contribution of DIC flux from the Himalayan glacierized basins to the ocean suggests a total ~0.02 Gg C km−2 yr−1 (1 Gg = 109 g), of which, ~0.009 Gg C km−2 yr−1 is released through silicate weathering (Na, K, and Ca bearing minerals) and ~0.011 Gg C km−2 yr−1 through carbonate (Ca-Mg bearing minerals) weathering. We observed that the present day atmospheric CO2 drawdown and its associated DIC fluxes in retreating Himalayan glacierized basins is dominantly controlled by carbonate weathering. Our findings indicate the importance of carbonate weathering from glacial terrains in carbon sink studies for global carbon models in elucidating climate change effects.