Stable isotopic compositions in precipitation over wet island in Central Asia

As a typical wet island in arid Central Asia, the Ili Valley located in northwestern China provides water resources for the oasis in the lower reaches. However, it is not clear whether its unique climatic characteristics will lead to different isotopes of precipitation and what is the major factor controlling the variation of precipitation isotopes in this region. Based on three sites spread over the Ili Valley, 297 precipitation samples were collected from May 2015 to April 2016. The delta O-18 and delta D values range from -37.8 parts per thousand to 3.2 parts per thousand and -261.5 parts per thousand to 34.5 parts per thousand, with a weighted mean -9.4 parts per thousand and -65.2 parts per thousand, respectively. A clear correlation exists between mean monthly delta O-18 values and mean monthly temperature, with R-2 = 0.68 for the mean monthly values increase of 0.91 parts per thousand per degree Celsius. A positive gradient of 0.32 parts per thousand/100 m was obtained from the Ili Valley when an annual weighted average of delta O-18 values was used. Considering the temporal and spatial variation of hydrogen and oxygen isotopes and d-excess value of precipitation, combined with the results from the HYSPLIT4.0 air mass trajectory model, we found that moisture source in the study area is considered mainly replenished by the westerlies, and the moisture recycle from local surface water and soil water around Yining cannot be ignored. Although the data covers a year, it can still provide a good database for studying hydrological cycle in Centeral Asian.