Vegetation and climate history reconstructed from an alpine lake in central Tienshan Mountains since 8.5 ka BP

High mountains are humid islands in arid central Asia, and alpine vegetation is sensitive to climate change, especially to temperature variations. Here we present a palynological sequence and discuss the past vegetation and climate changes based on core BY10A from the Swan Lake, an alpine lake situated at an inter-montane basin in the central Tienshan Mountains, Xinjiang, northwestern China. We collected 52 modern pollen surface samples at different elevations to aid in the interpretation of fossil-pollen data, which provide a reconstruction of vegetation and climate history for the last 8.5 ka (1 ka = 1000 cal yr BP). Artemisia and Amaranthaceae (= Chenopodiaceae) are the main pollen types in desert steppe zone below 1800 m elevation, while Poaceae and Picea dominate the mid-elevation forest steppe zone (1800-2800 m). Cyperaceae is the main indicator of high alpine meadows (>2800 m). From 8.5 to 6.9 ka, the vegetation was steppe meadow suggesting relatively warm climate. From 6.9 to 2.6 ka generally high values of Cyperaceae and peaty sediments indicate a fen environment and cooler, more humid conditions. Interrupting this mid-Holocene period is a 5.5-4.5 ka millennium of lacustrine sediments with lower Cyperaceae, higher Poaceae and Artemisia, and high values of Myriophyllum and Pediastrum indicating higher water levels and warmer temperatures. After 2.6 ka, pollen data indicate alpine steppe and warmer climate. The mid-Holocene pattern of cooler climate interrupted by a warmer period is consistent from other regional records from Xinjiang, including the Guliya ice core and Kesang Cave speleothem record. During the cooler periods, the regional record indicates that a weakened summer Asian monsoon is countered to some extent by a stronger winter monsoon. (C) 2015 Elsevier B.V. All rights reserved.