Holocene Climate And Environmental Changes Documented By Sediments From Lake Gahai In Qaidam Basin

The proxies of sediments from inland enclosed saline lakes in the marginal region of the Asian Monsoon may have documented the detailed Holocene climatic and environmental history as such lakes are sensitive in response to regional climate. In this study, a sediment core, GHB from Lake Gahai in Delingha Basin, Qinghai was analyzed systematically for the species assemblage and abundance of ostracods, carbon and oxygen isotopes of ostracod shells, and percent content of minerals. Based on AMS 14C dating, the hydrological process of Lake Gahai since the Holocene is reconstructed. The water level, temperature and salinity of the lake are discussed in addition to the regional climate changes during the past 12.8 ka. The climate change pattern and the possible mechanism in the study area is also briefly discussed through comparison of GHB record with those from adjacent regions. The main conclusions are reached as follows:(1) The environmental history documented by GHB core are devided into several stages. A cool and dry period dominated 12.8～11.3 ka BP, corresponding to the YD period and the lake was shallow. During the early- and mid-Holocene (11.3-7.8 ka BP), the climate was warm and wet and the lake was less saline. A warm but dry period occurred during 7.8～5.7 ka BP. Typical cold-wet climate situation appeared between 5.7 and 3.1 ka BP with lowered salinity and higher lake level. The lake reached modern state since 3.1 ka BP and experienced several dry and wet variations.(2) The GHB core recorded some typical centennial- to millennial-scale climate events, such as Younger Dryas cold event,8.2 ka BP cold event, Medieval Warm Period, and the Little Ice Age.(3) Regional comparison suggests a rough consistency of climate changes documented in Lake Gahai with that in Lake Qinghai. When ompared with the speleothem records, the Asian monsoon strength proxy, weak coherence is indicated, especially during the late Holocene. In addition to the local geomorphology of Qaidam Basin, interactions between the monsoon system and the westerlies may be responsible the climatic and environmental evolution in Lake Gahai area.