Thermal regime of a supraglacial lake on the debris-covered Koxkar Glacier, southwest Tianshan, China

摘要

A supraglacial lake was surveyed on the Koxkar Glacier in southwest Tianshan from July to September 2007 and July to September 2008, and the temperature variation characteristics of the lake, debris and debris-free ice were analyzed at different depths to determine the thermal regimes. In addition, the discrepancies of temperature variation characteristics were investigated for different geomorphic units of the ablation zone of the Koxkar Glacier. It was found that daily temperature variation curves for deep water are V-shaped because meltwater from the glacier surface at temperatures of around 0℃ feeds the lake and mixes with the relatively high-temperature surface water during the day. As the water temperature rises to approximately 4℃, the mixed water sinks and forms a low-temperature trough in the deep water of the lake in the middle of the day. The vertical lapse rate of the lake water temperature against depth (-0.33℃/m) has a magnitude lower than that of the debris (-4.29℃/m) and that of the debris-free ice (-0.38℃/m) in the Koxkar Glacier's ablation zone. The temperature curve for the surface water largely varied between the temperature curves for the debris at depths of 0.2 and 0.5 m. The surface thermal condition of the ablation zone is significantly affected by the daily weather, and there is a limited influence in debris at a depth of 1 m and in the lake at a depth of 5 m.