Glacier sensitivity to climate variability since MIS-2: Insights from monsoon dominated north-eastern Himalaya

Abstract

The present study investigates the stratigraphically sequential glacial landform evolution using moraine stratigraphy in the Lashar and the Chopta valleys (Thangu) of north Sikkim, eastern Indian Himalaya. The glacial and associated landforms have been dated using luminescence and radiocarbon dating techniques which has allowed an understanding of the causes, and patterns of glacier advances/retreat. Chrono-stratigraphy of multiple glacier advances reveals that the oldest glacier advance preserved in the region corresponds to the Marine Isotopic Stgae-2 (MIS-2; global Last Glacial Maxima - gLGM) while the subsequent advances are younger. Our data provides a record of four glacier advances, named Thangu Glacier Advance (TGA-I to TGA-IV). The oldest preserved glacier advance (TGA-I) has been constrained between 28±2.8 and 22±2.4 ka. The second prominent glacier advance (TGA-II) is correlated with the Younger Dryas cooling event based on pro-glacial sediment ages 11±0.8 and 9.9±0.8 ka. A minor advance/standstill, TGA-III seems to coincide with the early mid Holocene and may be an artifact of 8.2 ka cooling event. TGA-IV is represented by prominent terminal moraines close to the present day glaciers and would have possibly occurred during the mid-late Holocene cooling. Post-gLGM deglaciation is dated between 18±2.2 and 15±2.6 ka whereas the second deglaciation following TGA-II represented by pro-glacial lake sediments abutting the TGA-II moraines, is dated between 11±0.8 and 9.9±0.8 ka. A close correspondence of glacier advances with periods of temperature minima would imply that the glaciers have actively responded to cooler temperatures associated with the mid-latitude westerlies in response to global variations and retreated during the enhanced monsoonal phases.