While glacial receding due to climate change is a global concern, Indian researchers have reported historical evidence on the advancing of a glacier located above Leh in Northwest Himalaya.
The Puche glacier, they say, has made three advances in the past – the oldest around 30 thousand years ago (30ka) that persisted until around 20ka; another around 14ka that led the glacier to descend about 15 km; and the youngest one that remains undated and could be 12ka (the Holocene age).
The study1 by a multi-institutional team led by Anil Shukla of Physical Research Laboratory, Ahmadabad, found "morphological, sedimentological, and chronological" evidence from the glacial deposits (moraines) suggesting that the glacier had made these three advances.
Earlier studies to determine the age of the moraines – based on measurement of the concentration of radio-nuclides like Be-10 – overestimated the age of Puche glacier to be 90-110 thousand years, suggesting the role of the Indian Summer Monsoon (ISM) in its advancement, says Shukla. His team used the 'optically stimulated luminescence' dating technique to measure the concentration of trapped electrons in the quartz crystals extracted from the moraines. They found that the moraines are much younger – only 30-20 thousand years old. This corresponds to a period during which moisture from the westerly disturbances (originating in the Mediterranean region) "was the major feeder for the growth of Puche glacier and not the ISM", Shukla says.
Himalayan glaciers are the storehouse of fresh water contributing about 45% of the total river flow in the Indus, Ganges and Brahmaputra watersheds. Over 500 million people depend on this water for agriculture and economic practices. "Moisture from the mid-latitude westerlies is critical for the advancement and sustenance of the glacier rather than enhanced summer monsoon," the authors conclude. The study, they say, has implications in terms of reassessing the role of the ISM in nurturing the glaciers in the Ladakh and Karakoram.
1. Shukla, A.D. et al. Optical chronology and climatic implication of glacial advances from the southern Ladakh Range, NW Himalaya, India. Palaeogeogr. Palaeocl. 539, 109505 (2020) doi:10.1016/j.palaeo.2019.109505