Holocene vegetation and climate history at Hurleg Lake in the Qaidam Basin, northwest China

We present fossil pollen data and discuss their climatic interpretations from a 688-cm-long sediment core from Hurleg Lake, a freshwater lake located in the Qaidam Basin on the NE Tibetan Plateau, just beyond the northern limit of the East Asian summer monsoon influence. The reconstruction of the Holocene vegetation and climate history was aided by modern surface pollen analysis. The 14000-yr chronology of the sediment core was controlled by seven AMS 14C dates on plant macrofossils. The results of the surface pollen analysis showed that modern pollen spectra faithfully reflect the regional vegetation along a transect from alpine meadow to desert steppe and desert, so fossil pollen record can be used to reconstruct Holocene vegetation change. The pollen data showed that vegetation changed from desert before the Holocene to desert steppe dominated by Artemisia from 11.9 to 9.5 ka, desert dominated by Chenopodiaceae from 9.5 to 5.5 ka, and steppe desert dominated by Artemisia and Poaceae after 5.5 ka. This vegetation sequence indicates that climate was relatively wet before 9.5 ka, dry and variable from 9.5 to 5.5 ka, and relatively wet and stable after 5.5 ka. The climate pattern reconstructed from pollen data appears to be opposite to the paleoclimate pattern inferred at Qinghai Lake, 300 km east of our study site. That site shows a moist early Holocene during the insolation and monsoon maximum followed by a drying trend during the mid- and late Holocene. The contrast between the two sites suggests the importance of the position of the subtropical monsoon, the mid-latitude westerlies and interactions between local topography and regional climate. Our finding has important implications for understanding complex regional vegetation and climate responses to large-scale forcings in arid central Asia.