Paleoclimate Changes and the Evolution of Atmospheric Circulation in Selin Co on the Central Tibetan Plateau Since the Mid–Late Holocene

Selin Co, the largest lake on the Central Tibetan Plateau, is located at the junction of the Asian summer monsoon and the Westerlies, making it an ideal site for investigating the evolution of atmospheric circulation. In this study, variations in total organic carbon (TOC) and total carbonate contents, carbon and oxygen isotopic compositions of authigenic carbonates, together with grain-size parameters and changes in ostracod assemblages from lake sediments, are used to reconstruct the advance and retreat of the Asian summer monsoon and the Westerlies circulation since 6.20 ka. The regional climate evolution and the characteristics of specific climatic events in the Selin Co area are also discussed. The results indicate that from 6.20 to 2.21 ka, the Selin Co region was mainly dominated by the Westerlies. Lake level remained relatively high as it inherited from the highstand during the Holocene Megathermal, the supply of glacial meltwater also contributed. Between 3.32 and 2.21 ka, the regional climate experienced pronounced fluctuations. After 2.21 ka, the Indian summer monsoon became the dominant controlling factor. Nevertheless, weakened solar radiation led to reduced moisture transport by the monsoon, resulting in a gradual trend toward aridification and a progressive decline in lake level. The widely recognized 4.2 ka cold-dry event began at approximately 4.25 ka in the central Tibetan Plateau and persisted for about 370 years. It was characterized by predominantly cold conditions during its initial phase, followed by pronounced aridity during the middle to late stages, with superimposed temperature fluctuations. The Medieval Warm Period (MWP) was relatively short-lived, occurring between 1.15 and 0.79 ka, and was marked by a distinct early temperature increase followed by gradual cooling. After 0.68 ka, regional temperatures declined further, with modest cooling initially and a more pronounced temperature decrease after 0.39 ka, corresponding broadly to the Little Ice Age (LIA).