Distribution of Borehole Temperature at Four High-altitude Alpine Glaciers in Central Asia

The distribution of borehole temperature at four high-altitude alpine glaciers was investigated. The result shows that the temperature ranges from -13.4°C to -1.84°C, indicating the glaciers are cold throughout the boreholes. The negative gradient (i.e., the temperature decreasing with the increasing of depth) due to the advection of ice and climate warming, and the negative gradient moving downwards relates to climate warming, are probably responsible for the observed minimum temperature moving to lower depth in boreholes of the Gyabrag glacier and Miaoergou glacier compared to the previously investigated continental ice core borehole temperature in West China. The borehole temperature at 10 m depth ranges from -8.0°C in the Gyabrag glacier in the central Himalayas to -12.9°C in the Tsabagarav glacier in the Altai range. The borehole temperature at 10 m depth is 3~4 degrees higher than the calculated mean annual air temperature on the surface of the glaciers and the higher 10 m depth temperature is mainly caused by the production of latent heat due to melt-water percolation and refreezing. The basal temperature is far below the melting point, indicating that the glaciers are frozen to bedrock. The very low temperature gradients near the bedrock suggest that the influence of geothermal flux and ice flow on basal temperature is very weak. The low temperature and small velocity of ice flow of glaciers are beneficial for preservation of the chemical and isotopic information in ice cores.