Isotopic insights into cold region hydrology: Decoding isotopic signatures of snow and glacier in Khangeri glacier, North-eastern Himalaya. 

The hydrology of the glacier-fed systems plays a critical role in maintaining sustainability, water availability, and livelihood in the downstream region. The Khangeri glacier of the north-eastern Himalaya belongs to the Mago basin, which is a small catchment in the major Brahmaputra river system. Understanding the isotopic characteristics of these cold regions offers a unique lens to decode the dynamics of snow and glacier behaviour to the regional water resources. This study investigates the stable isotopic signature of snow, ice, glacier, and meltwater within the Khangeri glacier system, employing the stable isotopes of oxygen (δ18O) and hydrogen (δ2H) as tracers. The isotopic analysis was performed using the Liquid Triple Isotopic Water Analyser (L-TIWA) following the conventional analytical procedure for laser-based, off-axis integrated cavity output spectroscopy (ICOS). The isotopic analysis reveals distinct seasonal variations, with heavier isotope enrichment during the premonsoon period and depletion during the postmonsoon period. All the snow samples show regression lines with similar slopes and intercepts greater than the Global Meteoric Water Line (GMWL), but the glacier samples show a regression line with a lesser slope and intercept than the GMWL. This study also identifies the critical processes involved in the fractionation of isotopes during snow/glacier melting and isotope mixing, which shapes the isotopic signature of meltwater coming downstream. This isotopic study offers the significance of this tracer technique in understanding hydrological processes and predicting climate change on cryospheric hydrology.Keywords: Stable isotope, Snow, Khangeri glacier, North-eastern Himalaya, Mago basin