Abstract:

In order to reveal the characteristics and climatic controls on the stable isotopic composition of precipitation over Arid Northwestern China, eight stations have been selected from Chinese Network of Isotopes in Precipitation (CHNIP). During the year 2005 and 2006, monthly precipitation samples have been collected and analyzed for the composition of δD and δ¹⁸O. The established local meteoric water line δD=7.42δ¹⁸O+1.38, based on the 95 obtained monthly composite samples, could be treated as isotopic input function across the region. The deviations of slope and intercept from the Global Meteoric Water Line indicated the specific regional meteorological conditions. The monthly δ¹⁸O values were characterized by a positive correlation with surface air temperature (δ¹⁸O (‰) =0.33 T (℃)–13.12). The amount effect visualized during summer period (δ¹⁸O (‰) = –0.04P (mm)–3.44) though not appeared at a whole yearly-scale. Spatial distributions of δ¹⁸O have properly portrayed the atmospheric circulation background in each month over Arid Northwestern China. The quantitative simulation of δ¹⁸O, which involved a Rayleigh fractionation and a kinetic fractionation, demonstrated that the latter one was the dominating function of condensation of raindrops. Furthermore, the raindrop suffered a re-evaporation during falling processes, and the precipitation vapor might have been mixed with a quantity of local recycled water vapor. Multiple linear regression equations and a δ¹⁸O–T relation have been gained by using meteorological parameters and δ¹⁸O data to evaluate physical controls on the long-term data. The established δ¹⁸O–T relation, which has been based on the present-day precipitation, could be considered as a first step of quantitatively reconstructing the historical environmental climate.

Key words: δ¹⁸O, precipitation, water vapor origin, Arid Northwestern China (ANC)