黄土高原石笋记录的DO 25季风增强事件

STRONG EAST ASIAN SUMMER MONSOON DURING THE DO 25 EVENT RECORDED BY AN ABSOLUTE-DATED STALAGMITE FROM DRAGON CAVE, NORTHERN CHINA

基于山西龙洞L4石笋4个铀钍年代和110个氧同位素数据（δ18O），重建了深海氧同位素5d（MIS 5d）期间中国北方地区东亚夏季风强度变化的历史。石笋的L4δ18O序列在113.9±0.6ka B.P.突然负偏1.1‰，指示了Dansgaard-Oeschger（DO）25季风增强事件的开始。在MIS 5d晚期，L4石笋突然停止生长，结合湖北三宝洞δ18O值明显偏重，揭示东亚季风区可能经历了一次显著的弱季风过程。不同纬度相同生长时段高分辨率石笋δ18O记录对比结果表明：在113.9~111.3ka B.P.期间，亚洲夏季风强度明显增强，与减弱的南美夏季风强度呈“镜像”关系；石笋δ18O记录的DO 24与DO 25季风事件的强弱对比表明太阳辐射变化仍是调控千年尺度亚洲夏季风强度变化的主要因素；此外，MIS 5d期间东亚夏季风强弱变化也响应于北高纬地区气温的冷暖波动，表明高低纬气候系统在末次冰期早期仍可能存在遥相关关系。北大西洋热盐环流的周期性变化可能是导致两者耦合的原因之一。

The Dragon Cave （38°46＇N,113°16＇E,1600m above sea level） is located at transition between semi-humid and semi-arid areas on the Chinese Loess Plateau,where is very sensitive to the changes of the monsoon precipitation.In summer,the inflow of warm/humid air delivered by summer monsoon extends northwesterly into the interior as far as the China-Mongolia border.In winter,the southward-migrating Siberian High cold and dry air mass dominates the regional climate.More than 76% of the yearly precipitation （ca.530mm） falls in summer,from June to September.Stalagmite L4 was collected from the Dragon cave,ca.10km southeast of Shiquan Village in Wuxiang County,Shanxi Province,North China.Its length is 115mm,with a diameter ca.60mm.A total of 4 sub-samples were measured by an inductively Multi-collection coupled plasma mass spectrometry on a Finnigan-NEPTUNE in the High-precision Mass Spectrometry and Environment Change Laboratory,Department of Geosciences,National Taiwan University.The uncertainty of reported age is ±2σ.110 sub-samples for δ18O measurement were analyzed with on-line automated carbonate preparation system linked to Finnigan MAT-253 mass spectrometer at the Isotope Laboratory of College of Geography Science,Nanjing Normal University.Results are reported relative to Vienna Pee Belemnite （VPDB） and standardization was accomplished using NBS-19.Two-sigma reproducibility was ±0.06‰.High-resolution oxygen isotope profile established with 110 oxygen isotope and 4 230Th dates,provides a continuous history of East Asian summer monsoon （EASM） intensity for the period of Marine Isotope Stages （MIS） 5d.The δ18O abruptly decreased from -7.7‰ to -8.8‰ at 113.9±0.6ka B.P.,indicating of the onset of Dansgaard-Oeschger （DO）25 event in monsoonal China.After 111.3±0.6ka B.P.,the L4 abruptly creased growing,and the stalagmite δ18O from Sanbao cave in Hubei Province rapidly increased by 1‰ at the same time,which suggests the EASM again weakened at the end of the DO 25 event in East Asian monsoon region.Comparison of our record with previous published contemporaneous stalagmite records across monsoonal China shows that the Asian summer monsoon intensity indeed increased from 113.9ka B.P.to 111.3ka B.P.,which also was supported by the opposite changes of the South American summer monsoon during this interval.In addition,comparison between typical DO 24 and DO 25 monsoon events as recorded by Chinese stalagmites suggests that the insolation is the primary factor controlling the millennial-scale variability of the Asian summer monsoon precipitation in monsoonal China.However,the millennial-scale variabilities of the EASM are well related in time with cold and warm shifts of the North Atlantic climate conditions as constructed by European stalagmite records during the MIS 5d period.This consistence suggests that there is relatively strong teleconnection between the North Atlantic and East Asian region under low ice volume conditions of the early MIS 5,likely due to the periodic changes of the Atlantic thermohaline circulation.