长沙大气降水中稳定同位素变化及过量氘指示水汽来源

Variations of Precipitation Stable Isotope and Vapor Origins Revealed by Deuterium Excess in Changsha

基于2010年1月1日至2012年5月31日长沙日降水同位素资料,对长沙降水中稳定同位素、过量氘(记为d)的变化特征以及它们与降水、温度和湿度的关系进行了分析。研究发现:①在季风系统下,降水中稳定同位素、d均具有明显的季节变化,表现出夏半年的低值与冬半年的高值交替变化的特点;②降水中稳定同位素在不同时段均存在降水量效应和湿度效应,另外,夏半年中表现为反温度效应,冬半年则表现出温度效应;③综合考虑降水中d和δ18O与大气湿度的关系,可认为影响长沙降水中稳定同位素变化的主要原因与降水的气团性质有关。夏半年中,夏季风盛行,降水的水汽主要来源于西南季风、东南季风所携带的海洋水汽,空气湿度大,d小,重同位素在水汽输送过程中因不断冷凝而大大贫化,从而降水中δ18O(δD)较小;冬半年中,长沙受大陆性气团控制,降水的水汽则主要来源于西风带及当地蒸发,空气湿度小,降水中δ18O(δD)以及d均较高。

Variations of both stable isotope and deuterium excess （denoted as d） in precipitation as well as their relationship with precipitation, temperature and humidity were analyzed by using daily precipitation stable isotope data from January 1, 2010 to May 31, 2012. The results show that both stable isotopes and d in precipitation indicate obvious seasonal variation in the monsoon system, high value in the summer half year and low value in the winter half year. There are precipitation amour effect and humidity effect, in addition, anti-temperature effects in the summer half year and temperature effect in the winter half year. Considering both d and 5D in precipitation with atmospheric humidity, we deduced that the main causation of stable isotopic variations in precipitation is related to the property of rainfall air mass. In the summer half year, the water vapor is transported by the southwest and southeast monsoon from low latitude oceans, with high humidity, low stable isotopic ratios and d owing to the rainout of vapor on the transport way. Then, in the winter half year, the vapor is primarily from the westerly transportation and the replenishment of reevaporated vapor in inland, with low humidity, high stable isotopic ratios and d values in precipitation.