Reconstruction of Paleo-glacier equilibrium line altitudes during the last glacial maximum in the Nubra-Shyok valley, Ladakh

Abstract

Reconstructing paleoclimatic conditions in the westerlies-dominated Karakoram is essential for understanding the response of high-altitude arid regions to global climate variability. This study presents a reconstruction of the Last Glacial Maximum (LGM) extents of 15 glaciers in the Nubra–Shyok valley, eastern Karakoram, using preserved glacial geomorphology in combination with the GlaRe model. The valley, situated within the influence zone of the mid-latitude Westerlies, provides an exceptional setting to assess westerlies-driven glacial behavior. The reconstructions indicate that the main Siachen trunk glacier (NS1) covered an area of approximately 692 km², with modeled ice thicknesses ranging between 200 and 400 m, reaching a maximum of about 370 m. Equilibrium Line Altitudes (ELAs) were estimated using a weighted average of four established geomorphometric approaches (AABR, AAR, MELM, and THAR). The results indicate a marked ELA depression of ~ 700 m for the Siachen glacier during the LGM. Based on a locally derived lapse rate, this ELA depression corresponds to the lowering of summer temperature by 1.5–2.0 °C, suggesting that enhanced westerlies-induced precipitation moderated the regional expression of global LGM cooling. A distinct spatial ELA pattern is also evident: east-facing glaciers show significantly higher values than west-facing glaciers. This asymmetry reflects the combined effects of westerlies-controlled moisture distribution and differential solar insolation influencing ablation processes. These findings provide robust quantitative constraints on the extent of LGM glaciation and the prevailing paleoclimatic conditions in the valley, highlighting the primary influence of mid-latitude westerlies in modulating glacier dynamics and temperature regimes across this high-elevation region of the Himalaya.