GOBI DYNAMICS OF THE PAST 50,000 YEARS IN CENTRAL-EAST ASIA

The eolian sequences in the Mongolian Plateau suggest that the northern boundary of the Gobi deserts and its adjacent arid-semiarid areas dramatically retreated (southward) 5-7 times during MIS 2 and MIS 3 (between 10,000 and 57,000 14C yr BP): (1) from ~13,000 to ~16,000 14C yr BP, (2) from ~21,000 to ~25,000 14C yr BP, (3) around 29,000 14C yr BP, (4) around 31,000 14C yr BP, and (5) around 34,000 14C yr BP. One or two more retreats might have occurred during the earlier part of MIS 3 (between 35,000 and 57,000 14C yr BP). In comparison, the southern boundary of the Gobi deserts and its adjacent arid-semiarid areas retreated northward only three times during MIS 2 and MIS 3: (1) from 23,000 to 29,000 14C yr BP, (2) from 32,000-37,000 14C yr BP, and (3) from 40,000 to 50,000 TL yr BP. The maximal extent occurred twice: (1) from ~21,000 to ~16,000 14C yr BP and from ~13,000 to ~8,600 14C yr BP when the eolian deposition conditions extended at least from 55o N to 33o N. The extent of hyperarid and arid areas retreated to somewhere between 48 o N and 38 o N several times during MIS 3. During the Holocene, the northern boundary retreated most dramatically from ~8600 to 7000 14C yr BP when a well-developed Mollisol (~2 m thick) covered a large area in the Northern Mongolian Plateau. Minor soils (Entisols) and associated pollen assemblages indicate that the northern boundary retreated four times during mid-late Holocene: (1) around 4800 14C yr BP, (2) around 3800 14C yr BP, (3) around 3000 14C yr BP, and (4) during the past 1600 14C yr BP. The southern boundary retreated most dramatically from ~9000 to ~4000 14C yr BP and much less dramatically during the following periods: (1) from ~3500 to ~3100 14C yr BP, (2) from ~2900 to ~2400 14C yr BP, and (3) from ~2000 to ~1000 14C yr BP. To sum up, the climate did not change synchronously between the north and the south during MIS 3 and MIS2. and even during MIS1, suggesting that the summer monsoon has been changed asynchronously with the winter monsoon during the past 50,000 year and futher implying that the summer and winter monsoons might have not always forced each other.