Stable isotope composition of precipitation in the south and north slopes of Wushaoling Mountain, northwestern China

Abstract A study of spatial and temporal variability of precipitation isotope composition on the southern and north slopes of Wushaoling Mountain was conducted in order to explore the processes influencing its evolution. The analysis indicated that the isotopic composition, the slopes and intercepts of Local Meteroic Water Lines, altitude gradients and temperature effect are higher on the north slope than those on the south slope. The d -excess showed an increase from lower to higher altitudes, and the altitude gradients changed with season. The correlation coefficients between δ 18 O and d -excess decreased with increasing altitude due to weakening sub-cloud evaporation. Westerly wind principally dominates Wushaoling Mountain, so the relatively negative stable isotope values observed are related to the long distance transportation of water vapor in spring and winter. In summer and autumn, the locally strong sub-cloud evaporation cause relatively higher δ 18 O and lower d -excess. The results suggested that the sub-cloud evaporation has enriched the δ 18 O composition by 23%, 23%, 32%, 42% and 29% in May, June, July, August and September, respectively. In some circumstances, δ 18 O and δD were depleted at the end of multi-days rainfall events due to the rainout process. In addition, monsoonal moisture caused some negative δ 18 O in summer when an enhanced cyclonic circulation had developed on Tibetan Plateau. The study enhances the knowledge of isotopic evolution of precipitation and provides a basis for further study of isotopic hydrology in arid regions.