The Holocene history of Lop Nur and its palaeoclimate implications

The Holocene hydrological history of Lop Nur in northwestern China's Tarim Basin and its response to climate conditions are inferred from a relatively well-dated multi-proxy record including grain-size, pollen and spores, and soluble salt data. A dated pit section (YKD0301) with a depth of 570 cm in the center of the dry Lop Nur Basin was investigated. The sediments contain a total of twenty fining-upward cycles as a result of strong discharge from the catchment to the lake during relatively wet conditions. The fluvial sediments were probably widely dispersed by wind-driven waves and currents in the large and shallow basin of Lop Nur. Higher runoff and dilution of lake waters are also indicated by lower contents of soluble salt in the sediments and recorded ostracod shells of brackish and oligohaline to freshwater species. In contrast, sediment sections with smaller mean grain size and fewer flood layers are dominated by aeolian sediments which were accumulated during drier periods. Ostracod shells are mostly lacking from these sections, suggesting a higher salinity in the lake. Lop Nur experienced six stages during the last 9 ka. Relatively wet conditions existed between 9.0–8.9, 8.7–5.1 and 2.4–1.8 ka, with periods of increased aridity in between and after 1.8 ka. The lowest salinity was recorded between 8.7 and 5.1 ka which represents the wettest phase during the last 9 ka and probably the regional Holocene Optimum. Relatively wet climate conditions between 2.4 and 1.8 ka and dry conditions afterwards possibly first fostered and later on caused the devastation of the ancient Loulan Kingdom in the region. The uppermost sediments of the section represent a massive salt crust formed during the final desiccation of the lake in the last century. The effective moisture change pattern of the Lop Nur region is roughly consistent with synthesized Holocene moisture records for western China dominated by the westerlies.