Timing and extent of late Quaternary glaciation in the western Himalaya constrained by 10Be moraine dating in Garhwal, India

Glacial chronologies from the Himalayan region indicate various degrees of asynchronous glacial behavior. Part of this has been related to different sensitivities of glaciers situated in contrasting climatic compartments of the orogen, but so far field data in support for this hypothesis is lacking. Here, we present a new 10Be-derived glacial chronology for the upper Tons valley in western Garhwal, India, and initial results for the Pin and Thangi valleys in eastern Himachal Pradesh. These areas cover a steep gradient in orographic precipitation and allow testing for different climatic sensitivities. Our data provide a record of five glacial episodes at ∼16 ka, ∼11–12 ka, ∼8–9 ka, ∼5 ka, and <1 ka. In the Thangi valley, our results indicate a glacial episode at ∼19 ka, but no data are available for younger glacial deposits in this valley. At their largest mapped extent (∼16 ka), the two main glaciers in the upper Tons valley joined and descended down to ∼2500 m asl, which represents a drop of ∼1400 m compared to the present-day glacial extent. During the Holocene the two largest glaciers produced distinct glacial landforms that allowed us to reconstruct changes in the Equilibrium Line Altitude (ELA) over ∼20 km north-south distance that is presently associated with a steep gradient in rainfall. We observe that ELA-changes have been consistently ∼2 times higher for the glacier located in a presently wetter climate, pointing at different climate sensitivities, related to the amount of precipitation that they receive. At regional scale, our data is in reasonable agreement with other published glacial chronologies from the western Himalaya and suggest that glacial advances during the Holocene have been largely synchronous in this region. Comparison of glacial chronologies from the western Himalaya with other palaeoclimatic proxy data suggests that long-term changes in glacial extents are controlled by glacial-interglacial temperature oscillations related to the waxing and waning of the large northern-hemisphere ice sheets, while the timing of millennial-scale advance-and-retreat cycles are more directly related to monsoon strength.