Abstract
Runoff from high-elevation debris-covered glaciers represents a crucial water supply for millions of people in the Hindu Kush-Himalaya region, where peak water has already passed in places. Knowledge of glacier thermal regime is essential for predicting dynamic and geometric responses to mass balance change and determining subsurface drainage pathways, which ultimately influence proglacial discharge and hence downstream water availability. Yet, deep internal ice temperatures of these glaciers are unknown, making projections of their future response to climate change highly uncertain. Here, we show that the lower part of the ablation area of Khumbu Glacier, a high-elevation debris-covered glacier in Nepal, may contain ~56% temperate ice, with much of the colder shallow ice near to the melting-point temperature (within 0.8 °C). From boreholes drilled in the glacier’s ablation area, we measured a minimum ice temperature of −3.3 °C, and even the coldest ice we measured was 2 °C warmer than the mean annual air temperature. Our results indicate that high-elevation Himalayan glaciers are vulnerable to even minor atmospheric warming.
Highlights
A glacier’s thermal regime exerts a strong influence on its dynamics, mass balance, and its response to climatic change – a particular concern with rising atmospheric temperatures[1,2]
Debris-covered glaciers have a more complex surface topography and differing mass loss processes compared to clean-ice glaciers[13,14], complicating direct measurement of internal ice temperature
Seasonal variations in subglacial hydrology inferred from satellite-derived surface velocities suggest the presence of temperate ice at the base of high-elevation debris-covered glaciers[15,16]
Summary
Resistance was converted to temperature using a Steinhart and Hart[43] polynomial fitted to the manufacturer’s calibration curve, with a further correction using a freezing-point offset for each thermistor obtained from an ice-bath calibration Previous studies using such thermistors[44,45,46] suggest that with this secondary calibration, an accuracy of ±0.05 °C can be achieved. To estimate the CTS depth at Site 1, a line of the same gradient as for Site 2 was extrapolated from the mid-point of the error bar for the first thermistor below the seasonally-affected shallow ice layer (S1_15.0). This line intersected Tm at 20 m depth. When a line of the same gradient as Site 3 was used, it intersected Tm at 30 m depth
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