全新世季风气候突变事件和高频变率的黔西南石笋记录研究

This project provides a continuous oxygen isotope sequence based on annual-layer counting and U series dating from a 3.5 m-long stalagmite from Chengjiachun Cave in southwest Guizhou province. By combining the cave monitoring results and meteorological data, the project aims to understand the climatic significance of oxygen isotope and other multi-proxy data, thus to reconstruct an annually-resolved process of changes in Asian monsoon intensity and cave environment through the Holocene. Under the long climate backgrounds, it is instrumental to recognize the regional expressions of climate anomalies and their link to high-latitude climates. By comparing with the Δ14C, 10Be records, we can discuss the relationship between Asian monsoon and solar activities on decadal to centennial scales during the Holocene, to detect the patterns of decadal monsoon variability under different boundary conditions and the coupled mechanism with atmosphere/ocean circulations. Moreover, combined with global continent and ocean proxies and climate modeling results, we could distinguish the forcing dynamics behind the monsoon variability from internal or external factors, hence to provide basic evidence for forecasting the future trend of Asia monsoon variability.

本项目拟通过年纹层计数、U系测年法建立黔西南程家春洞一支3.5米长的连续石笋全新世氧同位素序列。结合洞穴野外观测结果以及气象气候资料明确氧同位素及其相关代用指标的气候意义，从而恢复研究区域全新世季风强度和洞穴环境的高分辨率演变过程。据长期演化背景和年际分辨率的氧同位素特征，识别类似于8.2 ka等异常气候突变事件的基本特征和发生规律，通过与格陵兰冰芯记录的对比，揭示高、低纬气候的相互关系；通过与反映太阳活动的Δ14C、10Be记录对比，探索全新世百年尺度亚洲季风与太阳活动的关系；识别不同边界条件下 (全新世早、中晚期) 十年际尺度季风变率的基本特征及其大气－海洋环流之间的耦合过程。与全球不同海陆代用指标和气候模拟结果的对比，区分地球内外因素对不同时间尺度季风气候的驱动作用，为预测未来亚洲季风气候走向提供其自然变率的理论依据。

本项目通过贵州省西南程家春洞穴石笋CJC-1的同位素和微量元素变化建立了21.5–0.2 kaBP平均分辨率为5.2 a的亚洲季风演化序列。项目实施后取得主要进展如下：（1）首次提供了从冰盛期到晚全新世长达21 ka的连续的高分辨率石笋同位素记录。（2）探讨了神秘期美国西南部大湖盆由大干旱向大湿润转型、大气CO2升高和Δ14C下降的原因。在盛冰期~19.5–17.5 ka时段，CJC-1石笋显示季风强度异常增强，达到Bølling-Allerød间冰阶水平，不同于盛冰期时季风减弱的模拟结果。此强季风事件与北大西洋温盐环流 (AMOC) 增强呈对应关系，说明海洋环流在盛冰期向欧亚大陆输送的热量足以引起季风增强。（3）通过对比CJC-1与格陵兰同位素记录，发现YD事件开始时亚洲季风环流的减弱过程要早于格陵兰温度的下降过程，表明YD事件并非由AMOC变化触发。（4）CJC-1 δ13C首次记录了北大西洋IRD事件，也与8.2 ka事件、格陵兰温度和太阳活动有明显的对应性，进一步支持了基于董歌洞石笋δ18O记录得出的北大西洋气候和太阳活动共同影响全新世东亚气候的理论。