Climatological significance of δ18 O in precipitation and ice cores: a case study at the head of the Ürümqi river, Tien Shan, China

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Abstract
Stable-oxygen-isotope ratios(δ18O)of precipitation and ice-core samples collected from the headwaters of the Urümqi river, Tien Shan, China, were used to test the relationship betweenδ18Oand contemporaneous surface air temperature (Ta). A strong temporal relationship is found betweenδ18Oin precipitation andTa,particularly for the monthly averages which remove synoptic-scale influences such as changes in condensation level, condensation temperature and moisture sources ( Yao and others, 1996). Linear fits as high as 0.95‰° C-1for precipitation events and 1.23‰° C-1for monthly averages are found. Although theδ18O amplitude in ice cores drilled at the nearby Ürümqi glacier No.1(~2 km from the precipitation sampling site) decreased dramatically compared to the precipitation samples, the ice-core records of annually averagedδ18are still positively correlated with contemporaneous air temperature, especially summer air temperature, at the nearby Daxigou meteorological station. Nevertheless, the relationship between the ice-coreδ18Orecords and contemporaneous air temperature is less significant than that for the precipitation samples due to depositional and post-depositional modification processes, which are highlighted by the successive snow-pitδ18Oprofiles from the Ürümqi glacier No.1. Our results might extend the application of high-altitude and subtropical ice-coreδ18O—Tarecords for paleoclimate reconstruction.