中文摘要：

据湖北省神农架永兴洞一支石笋的8个230Th年龄、648个δ18O数据,建立了晚全新世4.40～ 1.75ka B.P.时段平均分辨率为4a的东亚夏季风演化序列,其中在2.92～ 2.74ka B.P.期间,δ18O发生显著正偏,幅度达2.5‰,指示一个显著的弱季风事件（这里称之“2.8ka”事件）.该事件以夏季风缓慢减弱开始,迅速增强结束,事件内部有两个次一级的振荡旋回（两峰三谷结构）,在内部细节与转型特征上类似湖北和尚洞石笋δ18O记录的“8.2ka”事件,暗示发生在全新世这两个冷事件的驱动机制基本一致.这两个弱季风事件都发生在太阳活动明显减弱时期,并分别与北大西洋Bond 2和Bond 5冰漂碎屑事件同步,表明百年尺度的东亚季风环流的演化由太阳活动和北高纬气候共同驱动.

英文摘要：

The Yongxing Cave （31°35′N,111°14′E; 800m above sea level） is located at Mt.Shennongjia,Hubei Province,The terrain is averagely 1500m a.s.1.and generally become lower from SW to NE.The mean annual precipitation at the study site is between 1500mm and 2000mm,most of which falls between May to October.The relative humidity and temperature in the cave are above 100％ and 15℃,respectively.A stalagmite （No.YX57） was collected from the cave.This sample is 603-mm-long,and is composed of compact calcite deposition,without any porosity on the polished surface.Chronology for the stable oxygen isotopes （δ18O） is established by eight 230Th dates,which were conducted at the Isotope Laboratory of Geology and Geophysics Department Minnesota University,USA.The dating results are in stratigraphic order.A total of 648 δ18O measurements were obtained from along the growth axis,with an average temporal resolution of 4a.The analysis was performed with MAT-253 mass spectrometer,linked with automatic equipment,at the Isotope Laboratory of College of Geography Science,Nanjing Normal University.These results provide a detailed record of East Asian monsoon variability between 4.40ka B.P.and 1.75ka B.P.When compared with high-resolution and precisely-dated stalagmite DA from Dongge cave in Guizhou,the general replication of these o18O records during the contemptuous growth period suggests that variations of the stalagmite YX57 o18O is reliable and can reflect large spatial changes in the strength of East Asian monsoon circulation.Our high-resolution δ18O record reveals a striking weak summer monsoon event between 2.92 ～ 2.74ka B.P.At the onset,the o18O values progressively increase by 2.5‰ （from-10.48‰ to-7.98‰） and suddenly drop by 2.4‰ （from-7.68‰ to-10.09‰） at the end,forming a double peak and three plunging structure.These characteristics were consistent with the structure of ＂8.2ka＂ event recorded by stalagmite H4 from Heshang cave in Hubei.Dynamically,these two abrupt monsoon events m