Environmental changes documented by sedimentation of Lake Yiema in arid China since the Late Glaciation

In this study, a 6 m long core (16,000 BP) at the center of the dry Lake Yi ema, a closed lake of Shiyang River drainage in Minqin Basin of the arid no rthwestern China, was retrieved to recover the history of climate changes a nd lake evolution in the area. Five radiocarbon dates on organic matter wer e obtained. A chronological sequence is established based on these five dat es and other dates from nearby sites. Magnetic susceptibility, particle siz e and chemical composition were analysized for climate proxies. The proxies indicate that a drier climate prevailed in the Shiyang River drainage duri ng the last glacial. Lake Yiema was dry and eolian sand covered most part o f the lake basin. During the early and middle Holocene, a moister climate p revailed in the drainage. Climate became dry stepwise with an abrupt transi tion from one stage to another during the entire Holocene and became driest since about 4,200 BP. Maximum dry climate spells occurred at about 12,000- 10,000 BP and after about 4,200 BP. A dry climate event also existed at abo ut 7,600 BP. Periodical sand storms with about 400-yr cycle happened during the middle Holocene. Desiccation processes of the lake started at 4,200 BP , and were accelerated since the last 2,500 yrs by the inflow water diversi on for agriculture irrigation. During the past 2,500 yrs, the lake size has been closed associated with the human population, implying that the human impact has been accelerating the lake desiccation superimposed on the natur al climate deterioration.