全新世以来长江中游年际-年代际水热配置演化的石笋记录

Precipitation, temperature and its correlations are the main concerns of the global change. In recent decades, the climate is characterized by warm-dry or cold-wet conditions, instead of warm-wet or cold-dry conditions as it used to be in most parts of Eastern China. The reason for the anomaly is still unclear, which might just be an oscillation of the earth climate or might be a result from the anthropogenic greenhouse effect. A long-term record of the correlations between temperature and precipitation may provide a clue. However, the limitation of the chronology and the paleoclimate proxies makes it difficult to figure out the correlations between temperature and precipitation, especially at interannual-interdecadal scale. A continuous monitoring over ten years on Heshang cave located in Qingjiang valley, Hubei shows that the correlations between stalagmite carbon and oxygen isotope match well with those between temperature and precipitation, which provides a key proxy to reconstruct the temperature and rainfall correlations in geological time and might bring a breakthrough in this field. In this project, based on three stalagmites carbon and oxygen isotope measurements on each lamination, both inter-annual stalagmite carbon and oxygen isotope records during the Holocene could be reconstructed synchronously. The correlations between temperature and precipitation at interannual to interdecadal scale with its evolution history around the middle reaches of Yangtze River could be understood, which is helpful to investigate the climate forcing in the East Asian Monsoon area.

降水与温度及其组合（水热配置）是全球变化的重要研究内容。最近几十年中国东部的大部分地区，水热配置呈现暖干/冷湿特征，与传统认为的季风区暖湿/冷干的气候不同。这种反常是地球气候的间歇性颤动还是人类温室气体效应尚不清楚，需要了解长期的水热配置历史。然而，受年代学和气候替代指标的限制，过去陆地的水热配置研究相当困难，尤其是在年际-年代际时间尺度上。湖北和尚洞10余年的连续监测发现，石笋d13C-d18O的相关系数与水热配置（温度与滴水速率的相关性）高度契合，为建立本地区地质历史时期水热配置提供了关键的代用指标，由此可能带来水热配置研究的重要突破。本研究基于3支快速生长的年层石笋，通过逐层采样分析石笋碳和氧同位素组成，重建全新世年际分辨石笋碳和氧同位素的同步记录；在已经完成百年尺度的水热配置研究的基础上，重点建立年际-年代际时间尺度上长江中游的水热配置及其演化历史，探索东亚季风气候的驱动机制。

降水与气温是反映气候环境变化的重要要素。由于降水与气温之间存在着内在的热力学和动力学机制的联系，使得研究二者之间关系（即水热配置）的演变，相比于仅研究气温或降水单一变量更为重要。水热配置研究不仅有利于认识高温-干旱或低温-阴雨事件的驱动机制及其对区域工农业的影响，也有利于我们从能量循环和水循环耦合的角度去理解地球气候系统的整体行为。然而，局限于现代气象观测时段较短，且与工业革命之后人类二氧化碳大量排放时间重叠，目前的证据并不能很好地评估近年来极端气候灾害频发所代表的水热关系异常是自然变率还是人类温室气体效应主导，亟需长时间高分辨率的水热配置的历史数据及其相关分析予以支持。本研究通过对湖北清江和尚洞过去19年连续的高频监测，创建了一个基于石笋d13C-d18O耦合的区域水热配置新指标，用于重建长江中游全新世以来年际-年代际水热配置的演化历史。研究发现，在年际-年代际时间尺度上，全新世以来d13C和d18O的相关系数具有逐渐升高的趋势，指示水热配置的耦合加强，与季风、ENSO, PDO和AMO的变化有关。强烈的水热解耦出现在最近150年（工业化以来）和全新世大暖期（8-6kaBP），说明温度升高，容易引起长江中游的高温干旱。最近100年水热解耦出现的概率最高（34%），超过全新世大暖期（<28%），表明长江中游现代气候异常固然有地球气候间歇性颤动的贡献，但温室气体增暖的影响更为重要。结合古气候重建和气候模拟结果，我们认为未来全球继续变暖下长江中游的水热配置解耦的程度加深，高温热浪导致的干旱事件更加频繁，将严重地影响区域工农业生产和用水安全。