Assessment of chemical weathering mechanism and CO2 drawdown in distinct hydromicroclimate glacierized catchments, Western Himalayas

The present study investigates the role of varying subglacial drainage distribution, discharge patterns and reactive mineralogy in switching the chemical weathering mechanism and altering CO2 drawdown in distinct hydromicroclimate. Catchments with less glacierized area (Stok and Phutse in cold-arid zones) bestow high (ablation/accumulation)area ratio and large spatial extent of channelized subglacial conduits and, thus permit high specific discharge. Conversely, Chhota Shigri (CS) acquires large glacierized portion covered under accumulation zone. The low (ablation/accumulation)area ratio promotes the development of lesser channelized and more distributed subglacial drainage, allowing low specific discharge in CS basin. As a consequence of distinct drainage characteristics, carbonation reaction processed through atmospheric CO2 and calcite dissolution becomes the locus of solute generation in Phutse and Stok. Correspondingly, carbonate weathering mediated CO2 drawdown override and remains on the higher side than silicate weathering and thus makes the system potential sink to atmospheric CO2. Meltwater draining in Phutse and Stok shows neutral pH, low sulphate mass fractionation (SMF) and low pCO2. In contrary, Chhota Shigri augments predominant sulphide oxidation and carbonation via atmospheric CO2 as a major source of H+ for chemical weathering during low and high ablation seasons, respectively. Elevated role of sulphide oxidation in chemical weathering promotes high SMF, high pCO2 and lowered alkalinity during low ablation, which may act as a source of atmospheric CO2 in Chhota Shigri.