Paleoenvironmental and archaeological investigations at Qinghai Lake, western China: Geomorphic and chronometric evidence of lake level history

摘要

Qinghai Lake, located on the northeastern Qinghai-Tibet Plateau (Qing-Zang Gaoyuan), is China's largest extant closed-basin lake. Its position relative to major Asian climate systems makes it sensitive to global climate change. The lake has been the subject of numerous paleoenvironmental investigations including dating of shoreline features around the lake basin. Here we report new age estimates of shoreline features, geomorphic exposures and archaeological sites that contribute to the development of a lake-level history for Qinghai Lake and a landscape model of the Qinghai Lake Basin. Lake highstands above 3230 m (～ 36 m above the modern lake level) appear to date to late MIS 5, ～ 70-110 ka. The lake has had much more modest highstands since then: no evidence of MIS 3 lake stands higher than modern were found, and early Holocene highstands are no more than ～ 12 m above modern. If the age of highstands greater than 3230 m is confirmed through future work, then the Qinghai Lake Basin hydrologic balance prior to ～70 ka was dramatically different than after that time, including during the Holocene. A simple hydrologic balance model provides insights into the combination of precipitation, evaporation, and runoff generation needed to sustain the lake at 3260 m, the highest shoreline observed. A range of factors may explain the difference, primarily the relative strength of the East Asian monsoon. The basin was apparently subject to extensive alluviation during MIS 3, interrupted by widespread erosion and development of cryogenic features before and during the last glacial maximum (LGM). Loess that presently drapes much of the lower basin landscape began to be deposited after the LGM, ～ 16-18 ka. The landscape model outlined here has implications for archaeological visibility of early human occupation of the Qinghai-Tibet Plateau.