Holocene Vegetation And Environmental Change At Qingtu Lake In The Shiyang River Drainage

Holocene variability of the summer monsoons has been documents in a variety of proxy records in east and southwest China. However, its influence on regional climate in other parts of China is still poorly understood, especially further inland in north China and northwest China. Here we review a fossil pollen record from Qingtu Lake, on the northwestern Tengger Desert which is located near the limit of the present -day Southeast Monsoon limit. The paper aimed to reconstruct the Holocene vegetation and environment change at Qingtu Lake using pollen analysis and other indices and to understand its possible mechanisms .The 14,000-year chronology of the sediment core was controlled by 2 AMS ¹⁴C dates on bulk oraganic matter. The fossil pollen date showed that vetetation changed from desert steppe dominated by Artemisia in early Holocene, though desert dominated by Chenopodiaceae at 9.0-6.3 ka, desert steppe dominated by Artemisia at 6.3-2.5 ka, to desert dominated by Compositae at 2.5-1.0 ka and Chenopodiaceae after 1.0 ka. This vegetation sequence indicates that, in a generally arid context, climate was relatively wet in the early Holocene before 9.0 ka, dry at 9.0-6.3 ka, relatively wet at 9.0-6.3 ka, dry at 6.3-2.5 ka and dry and variable after 2.5 ka. Magnetic susceptibility, grain size and carbonate content of Qingtu Lake also reflect the climate drying and the lake gradually drying up before Holocene and after 2.5 ka.The climate pattern reconstructed from pollen date appears to the climate pattern from many records from nearby sites in Inner Mongolia and Loess Plateau, which shows a relatively dry early and wet mid-latitude Westerlies and local geomorphology in determining the regional climate. The finding has important implications for understanding complex regional vegetation and climate responses to large-scale forcings in arid central Asia.