永兴洞石笋记录的倒三-四冰期季风事件及其与南半球气候的联系

Studies on the characteristics of monsoon events and their correlation with southern hemisphere climate changes during the several recent ice-age cycles are a hotly debating topic in the palaeoclimatic community. This may help us understand the causes of the abrupt climate events and its potential correlation for climate changes at orbital scale. In this project, we present a high-resolution Asian monsoon record over a period from 410-240 kaBP, based on U-Th dates and δ18O data as well as lithological microsequences from multiple stalagmites, collected from Yongxing cave, Shennongjia Mountain, Hubei Province. This project focuses on the structure and pattern of millennial-scale climate variability in the third- and fourth most recent ice age cycles, and explores the evolution process and oscillation frequency of monsoon events under the different glacial climate boundaries. The Hulu/Sanbao cave isotopic records have characterized millennial-scale monsoon events during the last two ice age cycles, and the Yongxing record further extends the millennial-scale monsoon record back to the last four glacial cycles. Thus, our new record can detect the forcing factors of monsoon events after the Mid-Brunhes Event (MBE). Based on the correlation of millennial-scale events in the Antarctic ice core and Chinese stalagmite isotopic records, we would establish a relationship between Asian monsoon and Antarctic climate. This may help us test if the relationship of millennial climate events between two hemispheres in the last glaciation repeatedly occurred in the last four glacial cycles. By comparing the similarities and differences of abrupt climate changes between two hemispheres under the different climate boundaries, we can further discuss the potential forcing mechanisms associated with changes in solar radiation and global ice volume, and understand the importance of the potential feedbacks, such as the Meridional Overturning Circulation and/or the Intertropical Convergence Zone, in orbital climate changes.

研究数个冰期旋回季风事件的特征及其与南半球气候的联系，有助于深入理解全球性事件的成因及其对轨道气候变化的反馈机制。本项目基于湖北永兴洞7支生长在410-240kaBP时段石笋样品，通过U-Th年龄和石笋岩相学研究，建立氧碳同位素等高分辨率气候和环境代用指标序列。聚焦研究相对薄弱的倒数第三和倒数第四冰期旋回千年尺度季风事件的内部振荡和转型特征，探索不同边界条件下季风事件的突变过程和演变规律。综合已发表的葫芦/三宝洞最近两个冰期旋回的数据，分析最近四个冰期旋回内亚洲季风气候事件的准周期特征和控制因素。以千年事件为桥梁，对比中国洞穴石笋和南极冰芯记录，建立最近四个冰期旋回季风强度与南极温度的联系，诊断南北半球千年事件在轨道变化中的协同性和差异性。在分析太阳辐射、冰量变化与气候事件联系基础上，判断气候边界条件对事件耦合的阀值效应，了解温盐环流、热带辐合带等反馈机制在轨道变化中的可能作用。

研究数个冰期旋回季风事件的特征及其与南半球气候的联系，有助于深入理解全球性事件的成因及其对轨道气候变化的反馈机制。本项目主要研究冰期-间冰期旋回季风事件的内部振荡和转型特征，探索不同地球边界条件下季风事件的突变过程和演变规律。基于湖北永兴洞及其周边地区洞穴石笋U-Th年龄、氧碳同位素和岩相学研究结果，重建了亚洲季风高分辨率气候变化序列，取得的重要结果及其科学意义主要包括以下几个方面：（1）发现中低纬季风在轨道尺度上的影响因素除了传统认识上的岁差周期外，半岁差周期同样重要。显著的半岁差周期信号与南北半球30°太阳辐射极大值变化的半岁差周期基本吻合, 说明低纬降雨和温度变率对半球间低纬太阳辐射放大响应, 进而影响亚洲季风的强度变化.（2）石笋记录的亚洲季风变化特征与北大西洋海洋沉积非常相似，特别是5ka周期稳定贯穿石笋记录和海洋记录始终，说明千年尺度亚洲季风和北高纬气候变化的耦合关系不仅发生在末次冰期, 而且稳定持续在最近数个冰期旋回。（3）研究结果发现亚洲季风事件与南极温度呈线性相关，这种关系既包括发生在冰消期的大事件，也有一般意义上千年事件，甚至还有这些事件内部的次级变化，说明大气循环可能在半球间千年尺度信号的传输中发挥着重要作用。（4）研究表明60年准周期特征不仅出现在近现代季风变化中, 而且存在于末次间冰期, 甚至可能是间冰期亚洲季风系统的固有属性。理解这些气候特征形成的动力学过程和成因机制为气候预测在多种时间尺度上提供可靠的数据和理论基础.