Argha Banerjee, Ajinkya Jadhav, Sneha Potghan, Disha Patil, Deepak Suryavanshi

Geomorphological evidence suggests a subdued response of Himalayan glaciers during the Last Glacial Maximum (LGM), with relatively minor advances (~10 km) reported in several glacierised valleys across the region. This supports the hypothesis that a weakened Indian summer monsoon during the LGM largely counterbalanced the effects of a colder climate on Himalayan glaciers. In contrast, a recently reported major LGM advance (>100 km) along the main trunk of Chandra valley, western Himalaya, led to an alternative hypothesis that Himalayan glaciers did respond strongly to reduced LGM temperatures, in harmony with other glacierised regions in the world. We investigate this distinctive LGM response of Chandra valley glaciers using a two-dimensional ice-flow model, to show that this massive LGM advance was driven by a relatively modest lowering of equilibrium line altitude (ELA) by ~300 m. The vigourous response of Chandra valley glaciers to the ELA perturbations was governed by their high climate sensitivity due to the gentle slope of the main trunk valley. The relatively low value of estimated ELA change in this valley compares favourably with careful estimates reported from other parts of the Himalaya, indicating a prevalent weak climate forcing of glaciers in and around the Himalaya during the LGM. (This is a preprint of an article under review in Geology)