基于石笋钙同位素的长江中游地区近千年极端干旱事件的定量重建

The reconstruction of high-resolution aridity sequence over the last 1 ka has important science and social implications. Due to the merits of precise dating, higher temporal resolution, and plenty of paleoclimate proxies, stalagmites are well known archives for high resolution paleoclimate studies. The novel calcite isotope compositions have the potential to be considered as a proxy of extreme aridity. The preliminary studies conducted in Heshang Cave, Hubei Province, show the calcite isotope ratios are sensitive with the extreme drought events such as the famous 8.2 ky event and the ca. 1900 A.D. event in Yichang City. Based on this information, this project plans to analyze samples retrieved from the annual layers of HS-4 and HS-6 stalagmites through the last 1000 year. By comparing the annual resolution of calcite isotopic data and the precipitation in Yichang City over the last 150 years, we will try to develop a quantitative model between calcite isotope compositions and aridity. With this quantitative model, we will reconstruct the histories of extreme drought event over the last 1000 years in the middle Yangtze River, and explore the rhythms of extreme drought in this climate sensitive region. This study has important implications for future climate prediction and ecosystem management.

建立近千年来高分辨率的干旱序列有着重要的科学研究价值和社会意义。洞穴石笋定年准确、时间分辨率高、代用指标丰富，是进行高分辨率古气候研究的优良载体。前期在湖北清江和尚洞开展的研究发现，新近发展起来的石笋钙同位素非常有潜力用来定量指示当地极端干旱事件(如8200事件和1900年左右干旱事件)有效降雨量的变化。本项目将在前期工作的基础上，对和尚洞有年纹的HS-4和HS-6石笋进行年际尺度的钙同位素组成分析，结合有器测记录的极端干旱事件有效降雨量值，建立石笋钙同位素定量重建极端干旱事件有效降雨量变化的模型。进而利用建立的模型，定量重建长江中游地区近千年来的年际分辨率的干旱事件序列，探讨该地区近千年来年际分辨率的干旱事件发生的规律，为预测未来气候变化下干旱事件的演化提供理论依据。

洞穴石笋钙同位素在定量重建极端干旱事件方面具有很大潜力，因而石笋钙同位素重建是古气候研究的一个重要内容。本研究对和尚洞有年纹的HS-4和HS-6石笋进行年际尺度的钙同位素组成分析，结合有器测记录的极端干旱事件有效降雨量值，建立了应用石笋钙同位素定量重建极端干旱事件有效降雨量变化的模型。进而利用该模型，定量重建了长江中游地区近千年来的年际分辨率的干旱事件序列，探讨了该地区近千年来年际分辨率的干旱事件发生的规律。我们发现，1394-1498AD，1628-1716AD和1795-1822AD年三个历史时期都发生了极端干旱事件。其中，1628-1716AD时期与黄爷洞石笋氧同位素出现的正偏一致，表明此次干旱事件可能是全国大范围的一次干旱事件。此次大范围异常干旱气候，正好对应了明末清初这样一个朝代更迭社会动荡时期。进一步对其驱动机制进行研究，发现石笋钙同位素表现出来的三个极端干旱时期（1394-1498AD，1628-1716AD和1795-1822AD），正好对应于太阳辐射的三个极小期（史波勒极小期，蒙德极小期和道尔顿极小期），暗示太阳活动减弱期对长江中游小冰期水文振荡的调控作用。并且，太阳辐射的三个极小期有逐渐减弱的趋势，石笋钙同位素表现出来的三个极端干旱事件也有逐渐减小的趋势。但其与区域季风的关系仍不明确，有待于下一步的深入研究。