广西桂林凉风洞秋冬季滴水和沉积物氧同位素对极端降水的记录研究

The Effect of Extreme Precipitation on Stable Isotope Compositions of Drip Water and Sediments during Autumn and Winter at Liangfeng Cave in Guilin,Guangxi

近年来,全球环境变化导致的极端气候事件的发生频率剧增,引起了国内外学者的广泛关注。由于器测记录时间较短,因此需要通过精确连续记录古气候变化的石笋来解译极端气候事件的规律。本文针对桂林凉风洞2015年9月至2016年1月的大气降水、洞穴滴水和现代沉积物的氧同位素组成进行了高分辨率的监测。监测结果揭示了由于秋冬水汽源的改变,导致桂林地区大气降水δD、δ^(18)O同位素值显示逐渐偏正的季节性变化,并且建立了该区域大气降水线为:δD=8.8δ^(18)O+16.38。由于大气降水作为凉风洞水源补给唯一来源,使得洞穴滴水的δ^(18)O继承大气降水的δ^(18)O所蕴含的环境信息,进而记录在洞穴现代沉积物中。但是受到洞穴顶部岩溶表层带的平滑或者均一化的作用,使得洞穴滴水的δ^(18)O同位素值要偏正于大气降水的δ^(18)O同位素值。在极端降水信号输入岩溶表层带后由于存在不同的水文地球化学过程,从而导致洞穴沉积物对其极端降水事件的响应时间存在不同,并且在δ^(18)O同位素值也存在明显差异。因此,系统监测洞穴滴水、沉积物δ^(18)O同位素对外界环境信息的响应过程,能为量化或精确解译石笋δ^(18)O同位素记录所指代的古气候环境信息提供基础。

In recent years, extreme climate events have increased dramatically due to global environmental change. As environment information recording time is short, it is necessary to interpret extreme climate events in stalagmites. In this study, precipitation, drip water and sediments were monitored with high resolution from September 2017 to January 2018 in Liangfeng Cave, Guilin City, Guangxi. The precipitation samples were measured for δD and δ18O isotope values. The results indicate that δD and δ18O isotope compositions of precipitation have obvious positive variations caused by water vapor source in the study area. The local meteoric water line （LMWL） is δD = 8.8 δ18O ＋ 16.38. The precipitation is the only source for Liangfeng cave, its oxygen isotope signals are reflected in the drip waters, and are recorded in the sediments. Nevertheless, cave drip waters may be mixed caused by precipitation which dropped in the old days before entering the cave and precipitationwhich dropped in the old days affected by evaporation effect through the epikarst. Therefore, δ18O values of drip water show more positive excursion than precipitation. However,δ18O of the sediment response time of extreme precipitation events are different due to the influence of different hydrogeochemical processes. Therefore, monitoring δ18O of drip water and sediment response process to environmental intbrmation can provide accurate interpreting paleoclimate information recorded by oxygen isotope in the stalagmite.