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

AbstractStable-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 between δ18O and contemporaneous surface air temperature (Ta). A strong temporal relationship is found between δ18O in precipitation and Ta, 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-1 for precipitation events and 1.23‰° C-1 for monthly averages are found. Although the δ18O 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 averaged δ18 are still positively correlated with contemporaneous air temperature, especially summer air temperature, at the nearby Daxigou meteorological station. Nevertheless, the relationship between the ice-core δ18O records 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-pit δ18O profiles from the Ürümqi glacier No.1. Our results might extend the application of high-altitude and subtropical ice-core δ18O —Ta records for paleoclimate reconstruction.