新仙女木事件内部百年尺度弱季风事件的龙腑宫洞石笋记录

Centennial-Scale Monsoon Failure During the Younger Dryas Event Record in a High-Resolution Stalagmite from Longfugong Cave,Central China

基于湖北省神农架龙腑宫洞一支石笋(LFG21)7个U/Th年龄和461组氧、碳同位素数据,建立了末次冰消期12.42~10.53 ka B.P.平均分辨率达3 a的亚洲夏季风强度演化序列.LFG21石笋δ^(18)O详细记录了新仙女木事件(YD)期间的季风突变细节,揭示了YD事件内部的不稳定性.在YD事件结构特征和转型模式上,石笋记录与格陵兰冰芯δ^(18)O记录具有良好的一致性,支持北高纬驱动机制以及高低纬之间的气候联系.其中,在~11.71 ka B.P.氧、碳同位素明显正偏,δ^(18)O从-8.6‰快速正偏至-7.9‰,δ^(13)C从-7.4‰快速正偏至-6.0‰,指示YD内部存在百年尺度的弱季风事件,持续时间为~200 a.这些特征与南京葫芦洞石笋δ^(18)O记录H1事件的内部结构和转型特征十分相似,暗示两者很可能受到同一驱动机制的影响.通过高、低纬地质资料的对比研究和波谱分析,本文认为YD内部百年尺度季风突变事件可能与热带大洋水汽输送变化导致的亚洲季风区水文循环异常以及太阳活动密切相关.

A 461-mm long stalagmite from Longfugong Cave in Hubei province, cenrtal China,was 230Th dated and meas- ured with stable isotopic analysis to reconstruct a high-resolution（ 3 a）Asian Monsoon history over a period from 12.42 to 10.53 ka B. P., equivalent to the Younger Dyras （YD）episode. The overall pattern of δ^（18）O record, characterized by gradual onset but rapid end, agrees well with other high-resolution and precisely-dated speleothem records from Hulu, Ya- men and Qingtian Caves. A positive shift of δ^（18）O values from -8.6‰ to -7.9‰ at around 11.71 ka B.P. ,which is also mirrored in the carbon isotope composition with δ^（13）C values from -7.4‰ to -6.0‰,indicates a~ 200 a monsoon failure within the YD. The structures and transitions of YD event are equally registered by the δ^（18）O record of the H1 event （Heinrich 1 ）from Hulu Cave, possibly implying the same forcing mechanism. The calcite δ^（18）O record, which presents ab- rupt fluctuations and detailed instabilities in monsoon over the studied interval, shows coherence with ice-core δ（18）O record from Greenland, supporting the direct linkage between Greenland climate and monsoonal circulation. Based on the comparison with the bulk sedimentary titanium （Ti）records from the Cariaco Basin, we attribute the internal centennial monsoon failure to the southward displacement of the Intertropical Convergence Zone（ ITCZ）. The statistically significant periodicities of 128 a（δ（13）C） and-200 a（ δ（18）O ）from the wavelet analysis likely indicate the role of solar activity playing in monsoon,and this is further supported by the 10Be flux record derived from ice core.