HOLIVAR2006 Abstracts
Holocene vegetation and climate history at Hurleg Lake in the Qaidam Basin, north-west China.
Yan Zhao1, Zicheng Yu2,1, Fahu Chen1 and Emi Ito3
1MOE Key Laboratory of Western China's Environmental Systems, College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, China
2Department of Earth and Environmental Sciences, Lehigh University, 31 Williams Drive, Bethlehem, PA 18015, USA
3Limnological Research Center, Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Drive SE, Minneapolis, MN 55455, USA
Contact: Yan Zhao(yanzhao@lzu.edu.cn)
We present fossil pollen data and discuss their climatic interpretations from a 688-cm sediment core (HL05-2) 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 13,000 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, through desert steppe, to desert, so the fossil pollen record can be used to reconstruct Holocene vegetation change. Our fossil pollen data showed that vegetation changed from desert before the Holocene, through desert steppe dominated by Artemisia at 11.9-9.5 kyr and desert dominated by Chenopodiaceae at 9.5-5.5 kyr, to steppe desert dominated by Artemisia and Poaceae after 5.5 kyr. This vegetation sequence indicates that, in a generally arid context, climate was relatively wet in the Early Holocene before 9.5 kyr, dry and variable at 9.5-5.5 kyr, and relatively wet and stable after 5.5 kyr. Our pollen results demonstrated that high pollen concentration does not necessarily indicate dense vegetation cover under a moist climate, as often has been interpreted in palynological literature of arid regions. Also, local presence or expansion of Nitraria may be more likely to be associated with a high water table around the lake under a wet climate, as Nitraria depends mostly on soil moisture for its water demand. Our surface pollen analysis along a water-depth transect at Hurleg Lake suggests that Pediastrum can be used as a good indicator of lake-level changes, by providing a consistent interpretation of the down-core record.
The climate pattern reconstructed from pollen data appears to be opposite to the climate pattern from Qinghai Lake, 300 km east of our study site, which shows a moist Early Holocene during the insolation and monsoon maximum and a general drying trend during the mid- and Late Holocene. This contrasting pattern suggests the importance of interactions between the subtropical monsoon, the mid-latitude Westerlies, and local topography of the NE Tibetan Plateau in determining the regional climate. Our finding has important implications for understanding complex regional vegetation and climate responses to large-scale forcings in arid central Asia.
Yan is an associate professor at the College of Earth and Environmental Sciences, Lanzhou University. Her research interests include pollen analysis, plant macrofossil analysis, Quaternary vegetational history, and palaeolimnology.