桂林凉风洞洞穴滴水和现代沉积物对强降水/极端降水事件的响应关系研究

With global warming, extreme climate events have occurred frequently in recent years. So how to effectively predict extreme climate events is of great significance. Because meteorological instrumental recording time is short, stalagmites, which contain continuous records of ancient climate change, can be used to effectively explain the variation of extreme events. Cave monitoring is an important research basis for interpreting the information of stalagmites and building the bridge between meteorological instrumental recording and environmental pointer. The monitor’s systems in this project, based on Liangfeng Cave, Guilin, mainly include in precipitation, cave environment, drip water and modern sediments. To summarize their seasonal evolution features and explain their responds to the information of external environment, the carbon and oxygen stable isotopes, the element of precipitation, drip water and modern sediments are analysed. During the strong precipitation/extreme precipitation events, gets the cave features for the short time scales by high resolution monitoring; using stable isotope and element characteristics of drip water and modern sediments to quantitative or semi-quantitative reconstructions, researches the disturbance level of original signal value recorded by the environmental pointers in “Precipitation-Soil-Bedrock-Cave” system during epikarst in order to establish the response relationship of strong precipitation/extreme precipitation. At last discern the precipitation events in the stalagmite.

随着全球变暖，近年来极端气候事件频发，如何有效预测极端气候事件越来越受重视。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。而洞穴监测是解译石笋记录环境信息和搭建器测记录与环境替代指标之间桥梁的重要基础。本项目以桂林凉风洞为研究对象，系统监测大气降水、洞穴环境、滴水和现代沉积物，分析洞穴滴水和现代沉积物的碳氧稳定同位素、元素特征，总结季节性演变特征，解译其对外界环境信息的响应规律。在强降水/极端降水事件期间，通过高分辨率监测来查明其短时间尺度的响应特征；综合分析强降水/极端降水期间洞穴滴水和现代沉积物碳氧同位素和元素特征，定量化或者半定量化研究环境替代指标所记录的原始信号值在“降水-土壤-基岩-洞穴”垂直传递过程中受干扰的程度，建立强降水/极端降水事件的响应关系，最终实现在石笋中识别事件尺度的降水事件。

本项目对桂林凉风洞的大气降水、洞穴环境、洞穴滴水和现代沉积物开展了为期三年，每月一次的系统连续监测，总结季节变化特征，解译其对外界环境信息的响应规律。主要的研究发现如下：（1）洞穴CO2呈现夏季高、冬季低的季节变化特征。由于夏季土壤CO2升高，较多的降水下渗时将土壤CO2经基岩带入洞穴中，使得夏季洞穴CO2峰值升高。而强降水事件而产生的“活塞效应”也会导致CO2的骤然升高。（2）洞穴滴水的滴速变化对强降雨事件的响应明显，并且响应时间短（＜24小时）。洞穴滴水的水温变化也对强降雨事件有一定响应。（3）桂林地区的大气降水δD、δ18O呈现夏季偏轻、冬季偏重的季节变化特征。洞穴滴水的δD、δ18O落在区域大气降水线上，表明洞穴滴水继承了大气降水的同位素信息。洞穴滴水和现代沉积物的δD、δ18O变化趋势一致，说明现代沉积物继承了洞穴滴水的δD、δ18O信息。洞穴滴水和现代沉积物的δ18O在强降水事件后都发生了明显的负漂移，记录到了强降水事件的发生。（4）现代沉积物的沉积速率夏季高、冬季低，沉积速率的变化可以对季节的干湿变化作出响应。（5）洞穴滴水和现代沉积物的δ13C变化趋势一致，夏季偏轻、冬季偏重。δ13C在雨季主要受土壤CO2影响，在旱季则主要受降雨量影响。