新仙女木(Younger Dryas,简称YD)事件是发生在末次冰消期升温过程中北半球的一次急剧降温事件.文章基于福建西部仙云洞石笋(编号:XY IV-14)9个高精度~(230)Th年龄和233个氧同位素分析,建立了12.68~ 11.25 ka B.P.时段平均分辨率达7 a的东亚夏季风强度的演变序列.该石笋氧同位素记录最为显著的特征是在11.89~11.51 ka B.P.时delta~(18)O在38095 a内偏负约1.3,指示了YD事件缓慢的结束过程.与基于年层时标的我国北方苦栗树洞、南京葫芦洞和神农架青天洞石笋记录对比发现,仙云洞记录的YD结束过程的时间(38095 a)明显比苦栗树洞、葫芦洞和青天洞记录(38 a、10 a和11 a)长300多年.仙云洞石笋所记录的YD事件缓慢结束的特征与低纬菲律宾Palawan洞穴石笋记录十分相似.分析结果表明,受热带西太平洋海气耦合的影响,低纬水文循环过程的变化比高纬的气候突变要缓慢的多.
英文摘要:
The Younger Dryas( YD) event is a sharp cold event in the warming transition from the last deglaciation in the northern hemisphere approximately during 12.9 ~11.6 ka B.P. During the event, the Greenland temperature has dropped by 15 ℃. This climate anomaly appears to have been prevailing within the Northern Hemisphere. The pervasive hypothesis for the mechanism of the YD is the ice raft extended southward and large amount of cold and fresh water was integrated into the North Atlantic Ocean,and resulted in the attendant weakening of the Atlantic Meridional Overturning Circulation ( AMOC ). Xianyun cave ( 25°33'N, 116°59'E; 1200 m a. s. l.) is located in Laiyuan Town, Longyan City, Fujian Province, Southeast China. The cave is approximately 970 m in altitude, and overlain by 30 ~50 m of Permian limestone bedrock. The relative humidity inside is close to 100%. This region is strongly influenced by the East Asian Summer Monsoon ( EASM). The annual average temperature is 19 ~21 ℃ and the mean precipitation is 1600 ~1800 mm. Cave temperature is 17.5 ℃. The stalagmite ( number:XY IV-14) was collected on the bottom layer of Xianyun cave with 210 mm in height and 65 mm in diameter. An apparent unconformity was observable at a depth of 110 mm from the top of XYIV - 14, which is the sedimentary discontinuity. This study focuses on the 60 ~109 mm of this stalagmite. For stable isotopic measurements,5 subsamples were drilled with 0.5 mm diameter carbide dental burs along the growth axis between 60 mm and 65 mm and 228 additional subsamples were shaved from between 65 mm and 109 mm of stalagmite with a knife. Therefore, a total of 233 subsamples were drilled for delta~(18)O measurements between 60 mm and 109 mm. In this study, interannual-scale EASM variability 12.68 ka B.P. to 11.25 ka B.P. is reconstructed based on 9 high-precision ~(230)Th ages and 233 oxygen isotope data, yielding an average resolution of 7 a. This high resolution stalagmite delta~(18)O) record is characterized by negative shift process in the interval of 11.89~ 11.51 ka B.P. with an amplitude of 1.3%o within 38095a,which indicates the terminating of YD event. Comparing our record with published stalagmite records from Kulishu cave,Hulu cave and Qingtian cave,all of 4 stalagmites records captured the YD abrupt climate changes. However, changes in Xianyun cave are much more prolonged(38095 a),different from the abrupt changes in other caves ( 38 a, 10 a and 11a). This slowly ending of YD event recorded in the Xianyun cave stalagmite is very similar to that in the Palawan cave, Philippines. We conclude that the prolonged process of the Xianyun cave is influenced,to some extent, by ocean-atmosphere coupling processes over the tropical western Pacific Ocean. The hydro-climate of the tropical west Pacific may cause the different responses.