Trends and Features of Climatic Changes during the Late Quaternary Recorded in Ulaan Lake Sediments, Mongolia

Ulaan Lake, which is located in Umungobi Province, South Mongolia, was a large lake with 25 km in length and 15 km in width when the lake level was the highest. But the lake has been dried-up since 1990s, and only the vestige of this lake remains now. This phenomenon seems to be related to global warming, especially reflecting desertification of East Asia. Three sets of core sediment were collected at three sites of Ulaan Lake for delineation of the Quaternary paleoclimatic variations through integration of sedimentological, mineralogical and geochemical studies. The sediment is being dated using 14C and OSL methods. Core sediments are analyzed by grain size, sedimentary facies, X-radiography and magnetic susceptibility. In the 584 cm-long core, sediment from the top to 100 cm is dominantly composed of clay and homogeneous in color (reddish brown), whereas core interval between 100 cm and 400 cm is largely composed of silt and contain mottled features and several cm-thick grayish layer. Sediment below 400 cm horizon is composed of sand, silt and clay and includes features of bioturbation and soil bleaching. Magnetic susceptibility value sharply drops down at near 100 cm and increases sharply to 400 cm downcore, and stays nearly constant in the rest of the core. This observation indicates that the core site has been well-drained above ground water level with some faunal and floral activities. Plant debris are included ubiquitously and abundantly in the core interval from top to 150 cm, suggestive of root activity due to low groundwater level. The multi-proxy study of sediment cores will provide the continuous record of the paleoclimatic conditions in the southern Mongolia during the Late Quaternary period.