贵州黔西县水西洞石笋记录的末次冰期Heinrich Stadial 4气候突变事件

Last glacial Heinrich Stadial 4 abrupt climatic events recorded by a stalagmite from Shuixi cave, Qianxi County, Guizhou Province

末次冰期Heinrich Stadial 4气候突变事件(HS4事件)是发生于约40 ka B.P.(B.P.表示Before Present, Present为公元1950年)最为显著的一次海因里希冰阶事件,对其转型特征和精细结构的刻画有助于深入理解千年尺度气候突变事件的机制。本研究基于贵州黔西县水西洞SXG-3石笋的11个高精度230Th年龄和277个δ^(18)O数据,重建了40.77~37.17 ka B.P.时段平均分辨率为13 a的亚洲夏季风强度演变序列。该石笋氧同位素记录清晰地捕捉到了HS4弱季风事件,呈现出三阶段变化的特征,即:第1阶段(39.97~39.13 ka B.P.),石笋δ^(18)O在840±90 a内偏正1.32‰,夏季风缓慢减弱,对应于热带辐合带(Intertropical Convergence Zone,简称ITCZ)的南移和格陵兰气候快速变冷;第2阶段(39.13~38.35 ka B.P.),石笋δ^(18)O整体偏正,平均为-8.34‰,夏季风强度达到最弱,而南美季风达到最强,对应于ITCZ移动至最南端;第3阶段(38.35~37.59 ka B.P.),石笋δ^(18)O在760±89 a的时间内偏负至-9.25‰,对应于ITCZ的向北移动和格陵兰气候快速变暖。水西洞石笋记录的HS4事件三阶段变化特征与福建仙云洞记录十分相似,对应于NEEM(Northern Greenland Eemian Ice Drilling)冰心^(17)O-excess所反映的低纬水文循环过程变化,同时与南美Toca da Boa Vista(TBV)和Toca da Barrigude(TBR)洞穴石笋记录呈“镜像关系”。分析结果表明,在北半球高纬气候触发后,热带海洋和南半球热量的不断积聚及其随后的释放所引起的ITCZ的南北移动是造成这种三阶段变化的主要原因。

The last glacial Heinrich Stadial 4 event(HS4 event),which occurred at about 40 ka B.P.(“B.P.”is short for “Before Present, “Present”refers to 1950 AD),is the most significant Heinrich event. The characterization of its transition characteristics and detailed structure is helpful to further understand the mechanism of millennial-scale abrupt climate events in the last glacial period. We reconstructed the intensity evolution of Asian summer monsoon with average resolution of 13 a from 40.77 ka B.P. to 37.17 ka B.P. based on 11230Th ages and 277 δ^(18)O data derived from a stalagmite(SXG-3)at Shuixi Cave, Qianxi County, Guizhou Province. Our record captured the detailed structure of the HS4 event, showing three phages of change: In the first phase(from 39.97 to 39.13 ka B.P.),the stalagmite δ^(18)O showed a positive excursion by 1.32‰ within 840±90 a, indicating that the summer monsoon weakened slowly, associated with the southward shift of the Intertropical Convergence Zone(ITCZ)and the rapid cooling in Greenland area;in the second phase(from 39.13 to 38.35 ka B.P.),the stalagmite δ^(18)O was generally positive, with an average of-8.34‰. During this phase, the summer monsoon intensity reached the weakest point, while the South American monsoon reached the strongest point, corresponding to the ITCZ lingered at its southernmost position;in the third phase(from 38.35 to 37.59 ka B.P.),the stalagmite δ^(18)O was gradually negative to-9.25‰ at 760±89 a, corresponding to the northward movement of the ITCZ and the rapid warming of Greenland area. The three-phase structure of the HS4 event recorded in Shuixi Cave is similar to that recorded in Xianyun Cave, Fujian Province, and corresponds to the changes in low-latitude hydrological cycle processes reflected by the NEEM(Northern Greenland Eemian Ice Drilling)Ice core^(17)O-excess. It also represents a “mirror image”of the stalagmite records of the Toca da Boa Vista(TBV)and Toca da Barrigude(TBR)caves in South America. The analy sis results show that upon triggering the high latitude climate in the northern hemisphere, the north-south movement of the ITCZ caused by the continuous accumulation and subsequent release of heat in the tropical ocean and the southern hemisphere is the main cause of such three-stage change.