Evolution of chemical weathering processes and CO2 sequestration in the glaciated basins of Western Himalayas

Understanding of chemical weathering process involved in ionic elution helps in distinguishing the CO₂ sequestration rate at the different micro-climatic setup of Himalayan catchments. In the present study, we have selected three glaciated basins from two different climatic zones of Western Himalayas (Lato and Phutse from the cold-arid zone of Ladakh and Chhota Shigri from the monsoon-arid zone of Himachal Pradesh, India) for determining various solute sources, CO₂ sequestration rate and its control over melt-water quality. Solute sourcing models used in this work shows major cations like Ca²⁺  and Mg²⁺ are from crustal rock-weathering while Na⁺ and K⁺ sourced out from the sea-salt origin. However, major anions like SO₄^2- (> 85%) were derived from the crustal origin and HCO₃^- mostly derived from atmospheric sources (39% to 45 %) in all catchments except HCO₃^- contribution from carbonation dissolution and silicate weathering is ~29% and ~16% for Ladakh catchments compared to ~9 % and ~29% in Chhota Shigri respectively. The solute model also reveals that the contribution of sulphate oxidative mediated carbonate dissolution (SOCD) in HCO₃^- flux is relatively higher in Chhota Shigri (~16%) than others (~9%). It is also observed that catchment like Chhota Shigri having a combined network of channelized and distributed drainage patterns with lower specific discharge, more glacierized area, low pH, high pCO₂, Low molar ratio [Ca²⁺ + Mg²⁺]/[ Na⁺ + K⁺], high SMF (~ 0.4), low CO_{2 carbonate}/CO_{2 silicate} ratio (~1.3) show relatively more sulphide oxidative and silicate weathered products than other catchments. Conversely, presence of excess non-glaciated areas in Stok and Phutse having well-channelized subsurface discharge with high CO_{2 carbonate}/CO_{2 silicate} ratio (~10 to ~5) show enhanced carbonation via atmospheric CO₂ (CAC) and carbonate dissolution with high annual CO₂ sequestration. Thus, varying subglacial drainage system, specific discharge pattern and reactive rock-types with distinct hydro-micro-climatic set up alters the chemical weathering mechanism in these catchments and control meltwater quality.