季节分辨率现代石笋沉积记录与气候环境响应

The dominant characteristics of the East Asian summer monsoon are the seasonal variation of large-scale circulation and its associated persistent and heavy precipitation. Over the Yangtze–Huai River Valley, which is known as Mei-yu or Plum rain, frequently result in regional flood events. The model result showed these events was related well to the sustained strong Western Pacific Subtropics High from late Spring. This relationship, however, still has some uncertainty for the input data was limited and discontinuous. We need more rainfall information from proxy record long-lasting and continuously. In this project, we collected several modern deposit speleothem that has a seasonal resolution of Oxygen isotope. Firstly, we make sure the speleothem Oxygen isotope carried the real isotope information of the precipitation. Then we can establish a 50-year chronology of the history precipitation depending on the Mingxiaoling speleothem Oxygen isotope. Thirdly, we analyzed the phase relationship between the abnormal heavy Oxygen isotope events in precipitation and the extraordinarily Western Pacific Subtropics High as well as the Meiyu Heavy rainfall events summer after, then we may give a predict alarm of summer Meiyu Heavy rainfall events more than one months ago in the spring. At the same time, the seasonal resolution of Carbon isotope and trace elements could support us the information of environment pollution made by modern human being activity, such as sand/dust storm, acid rain and heavy mistiness.

季风区梅雨期是否会形成特大洪涝灾害一直是一个特别受关注的问题。模拟结果显示从春季开始西太副高的持续增强，是江淮地区特大梅雨异常降水事件的主要特征。然而，这些模拟结果还存在很多不确定性，需要大气降水观测数据的进一步支持。本项目以南京明孝陵季节分辨率现代石笋沉积物为研究材料，对其氧碳同位素，微量元素等指标进行对比分析，结合现场观测数据，重点解析石笋氧同位素在季节分辨率对大气降水信息的真实继承性，从而建立50年以来的具有季节分辨率的季风降水氧同位素时间序列。探讨石笋记录中氧同位素的春季正异常与西太副高春季活动增强以及其后夏季梅雨降水异常的相位关系，解析长时间尺度西太副高的春季异常活动与随后的夏季梅雨降水事件的耦合关系。为梅雨大降水灾害事件提供预警信号。同时，以碳同位素和典型微量元素为代表，解析人类活动与现代环境恶化的联系。

石笋氧同位素记录在古气候研究中占有重要地位，但其代用指标的古气候意义存在较大争议。尤其是缺少季节分辨率的材料与现代器测资料进行对比。本项目选择南京明孝陵现代石笋沉积，结合器测记录和监测结果，建立明孝陵石笋的高分辨率时间序列，并对其气候指代意义进行探讨研究。同时结合微量元素的测试，探讨人类活动对现代环境变化的贡献。我们重点关注了南京场降水同位素信息，收集了1987年6月至1992年12月全球大气降水同位素观测网(GNIP)数据，自2015年1月至2019年12月，我们对南京地区每场大气降水的同位素连续采样测试，探究场降水和月降水δ18O变化的水汽源指示意义。利用石笋现代沉积监测，表明石笋δ18O能记录场降水的信号，并且明孝陵石笋δ18O记录每个峰谷旋回代表一年，石笋δ18O值对大气降水δ18O具有很好的线性继承，波动形式和波动幅度几乎相同，确认了石笋记录了大气降水的信息。有几项初步认识：(1)南京地区的降水稳定同位素与中国东部季风区其他地点的大气降水方程线相近。 (2)南京地区大气降水根据水汽源地的不同可以分为五类：欧亚大陆水汽、西太平洋和南海水汽、西风远源水汽、局地近源水汽和印度洋水汽。五类降水δ18O平均值分别为：-3.66‰、-6.65‰、-6.45‰、-1.64‰和-8.97‰。持续降水中存在雨除效应，随着降水时间延长，降水中δ18O逐渐贫化。持续降水事件中不同水汽源气团的转换造成了δ18O剧烈波动，不同源地的水汽变化对降水δ18O的影响要比雨除效应的影响更加显著。 (3)南京地区大气降水δ18O季节变化明显，呈现春季最富集，夏季最贫化的特征。通过水汽、风场图结合HYSPLIT4拉格朗日后向轨迹模型结果分析，南京地区的大气降水反映了水汽源的变化，在一定程度上能示踪水汽来源。