Effect of the El Niño–Southern Oscillation on hydrogen and oxygen isotope ratios of precipitation in Guilin, SW China

This study monitored the isotopic compositions of precipitation in Guilin as well as the influence of El Niño–Southern Oscillation (ENSO) on the isotope ratios and water vapour sources from 2015 to 2016. The results indicate that the lower isotope values of precipitation from ocean water vapour source are affected by long transport distance and fractionation during summer and autumn. In contrast, the isotope values of winter and spring precipitation are affected by continental air masses and their evaporation sources yielding higher values. The intercepts of the local meteoric water line in Guilin are larger than those of the global meteoric water line, which is typical for subtropical monsoon climate. During the El Niño event, development of anomalous anticyclonic circulation enhances the northbound transport over the western Pacific and brings abundant water vapour to the southern part of China. During El Niño event prevailing period, precipitations exhibit a lower δ18O value and low d (deuterium excess) value, indicating that the 2015/2016 ENSO event had a significant effect on the precipitation distribution, precipitation amount, and isotope ratios in regional precipitation.

本研究于2015至2016年间，对桂林地区降水的同位素组成，以及厄尔尼诺-南方涛动（El Niño–Southern Oscillation, ENSO）对降水同位素比值与水汽来源的影响进行了监测。研究结果表明，夏秋季来自海洋水汽源的降水同位素值偏低，这一现象受长距离输送与同位素分馏作用的影响。与之相反，冬春季降水的同位素值偏高，其主要影响因素为大陆气团及其蒸发源。桂林地区局地大气降水线的截距大于全球大气降水线，这一特征符合亚热带季风气候的典型特点。在厄尔尼诺事件发生期间，异常反气旋环流的发展增强了西太平洋区域的北向水汽输送，为中国南方地区带来充足水汽。在厄尔尼诺事件盛行期，降水的δ¹⁸O值与氘盈余（deuterium excess, d）值均偏低，表明2015/2016年厄尔尼诺-南方涛动事件对区域降水的分布、降水量及同位素比值均具有显著影响。