Melting of the Chhota Shigri Glacier, Western Himalaya, Insensitive to Anthropogenic Emission Residues: Insights From Geochemical Evidence. Issue 19 (29th September 2021) - Nizam, Sarwar
Abstract: Himalayan glaciers are invariably covered by supra‐glacial debris. Of these glaciers, the Chhota Shigri Glacier (CSG) in the western Himalaya has minimal debris cover (3.4%), yet has a comparable melt rate to other Himalayan glaciers. Utilizing osmium isotopic composition, and major and trace element geochemistry of cryoconite, a dark colored aggregate of mineral and organic materials on the surface of the ablation zone of the CSG, we show that the surface of CSG is essentially free of anthropogenically emitted particles, contrary to many previous findings. Given this and the overall lack of debris, we conclude that the high melt rate of CSG is primarily related to the increase of the Earth's near‐surface temperature linked directly to global warming. Therefore, the future meltwater supply for glacial‐fed rivers originating from Lahaul and Spiti region would be most vulnerable for >50 million population living downstream and requires immediate attention. Plain Language Summary: Industrially derived particles are commonly deposited on Himalayan glaciers and have been proposed to be a major driver of glacier melting. Yet, the abundance of such material is highly variable across the Himalaya. The Chhota Shigri Glacier system despite having minimal debris cover and limited anthropogenic emission residues has experienced high ice volume loss since the end of the 20 th century (Azam et al., 2019, https://doi.org/10.1016/j.jhydrol.2019.04.075 ). We surmise that the elevated glacial mass wastage in Lahaul Spiti valley of the western Himalaya is much likely insensitive to anthropogenically sourced pollutants but primarily climate controlled as claimed by previous studies (Azam et al., 2014, https://doi.org/10.5194/tc-8-2195-2014 ; Gantayat et al., 2017, https://doi.org/10.1017/aog.2017.21 ). Key Points: This study presents first osmium isotopic composition on glacier surface impurities from the Himalaya Osmium isotopes and trace metal composition showed predominantly crustal sourced input Anthropogenic emission residues are not one of the significant drivers of glacier melting in the western Himalaya, as observed elsewhere