A 10-yr thermal regime of permafrost beneath and adjacent to an alpine thermokarst lake, Beiluhe Basin, Qinghai-Tibet Plateau, China

摘要

Thermokarst lakes are distributed widely in permafrost regions on the Qinghai-Tibet Plateau (QTP), China. Better knowledge of ground thermal variability beneath and around thermokarst lakes is important for understanding future landscape development and hydrological changes. At a typical undisturbed small, shallow, alpine thermokarst lake in the Beiluhe Basin on the QTP, ground temperatures beneath and adjacent to the lake were monitored at four locations with maximum 30 m depth from the lake center to natural ground. The lake is elliptical with an area of similar to 700 m(2) and maximum water depth of 0.6 m. Permafrost was present beneath and adjacent to the lake during the monitoring period. However, supra-taliks were present above the permafrost table beneath the lake before monitoring of ground temperature began, but were absent around the lake. The supra-permafrost taliks beneath the lake have thickened over time. The difference in mean permafrost table depth between the lake center and natural ground reached 5.14 m, and permafrost table depths increased beneath the lake, but changed indistinctively around the lake. Mean annual ground temperatures at different depths (5, 10, 20 and 30 m) were higher beneath the lake than around the lake, and mean increasing rates of ground temperature were also greater beneath the lake than around the lake. Ground temperature differences between the lake bottom and natural ground surface are important for understanding ground thermal patterns beneath and around thermokarst lakes.