[1] Dune fields in parts of northern China contain important stratigraphic records of late Quaternary change in the East Asian monsoon. In this study, 33 new optically stimulated luminescence (OSL) ages and other measurements from aeolian sediment sections are used to reconstruct the timing of wet-dry climate variation in the Mu Us and Otindag dune fields of north China. The results indicate dune activity and dry climate in the last few hundred years, 14 ka to about 7 -8 ka, and 50 ka to 60 ka. The dunes were mainly stable, implying a wetter climate, between about 7 -8 ka and 2.4 ka. These results imply a lag of several thousand years between peak summer insolation at 10-11 ka and high summer monsoon rainfall after 7 -8 ka. In the investigated regions, the monsoon climate may not respond directly to orbital forcing over millennial time scales. Land surface feedbacks may account for lagged dune field response.

The Last Glacial Maximum (LGM, and the Holocene Optimum (HO, c. 9-5 ka) were characterized by cold-dry and warm-wet climates respectively in the recently geological Earth. How Chinese deserts and sand fields responded to these distinctive climatic changes is still not clear, however. To reconstruct environments of the deserts and sand fields during the LGM and HO is helpful to understand the forcing mechanisms of environment change in this arid region, and to test paleoclimatic modeling results. Through our long-term field and laboratory investigations, 400 optically stimulated luminescence (OSL) ages and more than 100 depositional records in the Chinese deserts and sand fields were obtained; on the basis of these data, we reconstruct spatial distributions of the deserts and sand fields during the LGM and HO. Our results show that the sand fields of Mu Us, Hunshandake, Horqin and Hulun Buir in northern and northeastern China had expanded 25%, 37%, 38% and 270%, respectively, during the LGM; the sand fields of Gonghe in the northeastern Qinghai-Tibetan Plateau had expanded 20%, and the deserts of Badain Jaran, Tengger in central northern China had expanded 39% and 29% separately during the LGM; the deserts of Taklimakan, Gurbantünggüt and Kumtag in northwestern China had expanded 10%-20% respectively, compared to their modern areas. On the other hand, all of the sand fields were nearly completely covered by vegetation during the HO; the deserts in northwestern and central northern China were reduced by around 5%-20% in area during this time. Lakes in this arid region were probably expanded during the HO but this conclusion needs more investigation. Compared with the geological distributions of deserts and sand fields, human activity has clearly changed (expanded) the area of active sand dunes at the present time. Our observations show that environmental conditions of Chinese deserts and sand fields are controlled by regional climate together with human activity. deserts and sand fields in China, Last Glacial Maximum, Holocene Optimum, OSL dating, active sand dunes Citation:

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