19. Lake Terkhiin Tsagaan

Lake Terkhiin Tsagaan, a volcanic freshwater lake, occurs in the Terkh River valley of the Khangai Mountain Range in central Mongolia. The lake plays an important role in the hydrological system of the North Arctic Ocean drainage basin through the activities of Terkh, Suman, Chuluut, Ider, and Selenge Rivers and Lake Baikal the lake constitutes an extraordinary scenery in the Khangai region, and Terkh River in the west, Suman River in the east, and the basaltic landscape of Mt. Khorgo in the northeast are notable. Lake Terkhiin Tsagaan responds to the climate change with a slow rate as the lake gained an area for only 0.51 km² during the last 45 years. The short-term changes of the lake area are directly related to the fluctuations of annual and winter precipitations. Meanwhile, the long-term changes of the lake area are related to the rises in annual, summer, autumn, and spring average air temperatures, leading to thawing of snow cover and permafrost in the Khangai Mountain Range to discharge into the lake. The linear regression analysis shows that the lake area between 1970 and 2015 was moderately related to the annual precipitation (R² = 0.47), but not clearly related to the annual average air temperature (R² = 0.0186). The correlation analysis shows that the lake area during 1970–2015 had a moderate positive correlation with the precipitation (r = 0.685) and a weak negative correlation with the air temperature (r = −0.136). Physical and chemical properties of stratigraphic sequences of sediments in Lake Terkhiin Tsagaan indicate this lake to be a montane type with high contents of organic matter and biogenic silica and fine sediments, implying warm and humid climate conditions in the Khangai region within central Mongolia at that time of their deposition.