²¹⁰Pb Dating Of The Miaoergou Ice Core From The Eastern Tien Shan, China

Ice core was used to study the past climate change as one of the important approaches because of its distinctive characteristics such as high fidelity and resolution, large amount of information, long time series and spotlessness. Ice core records not only the change of the past climate, but also the various factors, such as solar activity, volcanic activity and greenhouse gases etc., that affect the climate change. The impacts of human activities on the environment also can be found form ice core record. Ice core is a good indicator of past climate and environmental change. Accurate dating is an essential prerequisite for the correct interpretation of paleoclimatic information from ice core records. In AD2005, two ice cores with lengths of58.7and57.6m respectively to bedrock were recovered from the Miaoergou flat-topped glacier (43°03’19"N,94°19’21"E;4512m a.s.l.), eastern Tien Shan. This study mainly dated one of the ice cores (57.6m) through210Pb dating method to study the environmental information record of the past climate and environmental change in this area. The results were showed as following:(1) An age of AD1851±6at a depth of41.5m (35.2m w. e.) was determined. At the nearby oasis city of Hami (-80km from the Miaoergou flattopped glacier) the annual precipitation rate is38mm w. e. y’1. With the effects of global warming, Miaoergou glacial meltwater is a major water supply for local residents.(2) The surface activity concentrations of210Pbex was found to be～400mBq/kg, which is higher than observed at other continental sites such as Belukha, Russia, and Tsambagarav, Monglia, which have surface concetrations of280mBq/kg.(3) The estimated210Pb age-depth relation change is linear, which indicates a thinning of annual-layer thickness with depth does not exist in Miaoergou flattopped glacier. This phenomenon is the result of factors such as the high altitude and the flat terrain of Miaoergou glacier, the low glacier temperature and the large amount of ice snow accumulated in warm season etc.(4) The210Pb dating agrees within error well with the bomb horizon during AD1963at11m w. e. but also with the annual counting result of AD1953at14m w. e. The results of different dating methods are therefore highly consistent. We conclude the210Pb analysis is a suitable method for obtaining a continuous dating of the Miaoergou ice core for～150years, which can also be applied to other ice cores recovered from the mountains of western China.