敦煌盆地降水稳定同位素特征及水汽来源

基于敦煌盆地2012年11月至2013年11月降水氢、氧稳定同位素数据 (δD、δ¹⁸O和d-excess),结合GNIP降水同位素监测资料和HYSPLIT 4模型对降水后向气团传输路径模拟结果,对敦煌盆地降水稳定同位素特征及水汽来源进行研究。结果表明:敦煌盆地降水δD和δ¹⁸O存在明显的季节效应,即降水δD和δ¹⁸O具有夏高冬低的变化特征;同时降水δD和δ¹⁸O表现出显著的温度效应,温度每升高1 ℃,δD增加6.89‰,δ¹⁸O增加0.92‰。敦煌盆地局地大气水线(LMWL)为δD=7.45δ¹⁸O+2.72(R²=0.98),受降水二次蒸发的影响,其斜率和截距均低于全球大气水线(GMWL)。降水d-excess受当地气温和相对湿度的影响,冬半年(11月至次年4月)偏正,夏半年(5-10月)偏负。从全年来看,敦煌盆地降水水汽主要来源于西风输送,冬季和春季受极地气团的影响,夏季部分降水事件受西南季风和局地再循环水汽的影响。

Variation of Stable Isotopes and Moisture Sources in Precipitation at the Dunhuang Basin in Northwest China

In this study, event-based precipitation samples collected from October 2012 to October 2013 in the Dunhuang Basin in Northwest China, GNIP data and HYSPLIT model have been used to constrain the stable isotopes variations and moisture sources. The δD, δ¹⁸O and d-excess showed distinctively seasonal variations: with more positive δD, δ¹⁸O and lower d-excess values in summer and more negative δD, δ¹⁸O and higher d-excess values in winter. The relationship between local air temperature and stable isotopes in precipitation exhibited significant positive correlations, with a gradient of 6.89‰·℃^-1 for δD and 0.92‰·℃^-1 for δ¹⁸O. The local meteoric water line (LMWL), established as δD=7.45δ¹⁸O+2.72(R²=0.98), had a lower slope and intercept than the global meteoric water line (GMWL), which was attributed to the effect of secondary evaporation, especially in summer. The variability of d-excess values in the Dunhuang Basin was mainly induced by the changes of air temperature and relative humidity. Generally, the moisture in the Dunhuang Basin was dominantly derived from westerly air masses all year round, and the region can receives polar air mass moisture transport in winter and spring, while some precipitation events was attributed to the water vapor transport from the southwest monsoon and local recycle moisture.