早全新世季风演化的高分辨率石笋δ^(18)O记录研究——以河南老母洞石笋为例

Early Holocene Monsoon Evolution of High-resolution Stalagmite δ^(18)O Records: in Henan Laomu Cave

基于豫西老母洞LM2石笋8个高精度230Th年龄,449个氧碳同位素,建立了达十年际分辨率的8.2~10.9 ka B.P.亚洲季风变化的δ18O记录序列。老母洞石笋δ18O值最为偏负达-12.0‰,最偏正为-8.2‰,振幅达3.8‰。早全新世10.13~10.9 ka B.P.时段内,河南西部老母洞石笋和东石崖石笋,陕西九仙洞C996-2石笋δ18O曲线揭示该时段内季风稳定,而中国南方的衙门洞石笋、三宝洞石笋和极地冰芯GRIP记录揭示该时段季风逐渐增强;同时季风达到顶峰的时期也不相同,进一步说明中国南北方早全新世10.13~10.9 ka B.P.时段季风演变过程的差异,可能与中国南北方气候的响应机制有关。从早全新世平均分辨率10年的LM2石笋记录中识别出8.2 ka,9.5 ka,10.2 ka和10.9 ka显著弱季风事件,尤其是8.2 ka和9.5 ka事件。对比分析老母洞与已发表的高分辨率石笋δ18O记录发现:石笋所揭示的某些冷事件发生时间在亚洲季风区存在差异,主要表现在事件内部变化特征及趋势上。LM2石笋δ18O曲线并没有明显记录9.3 ka弱季风事件,而是在9.3~9.6 ka B.P.左右记录了一个弱季风事件,与DSY09(2009)、Y1、HS-4记录相似,表明在该时段内存在季风的减弱事件,但是氧同位素传输的复杂性,使其在南北方表现不同。此外,在LM2石笋δ18O的8.2 ka B.P.开始时段,氧同位素曲线阶段性下降,且变幅达3‰,与Zhang等研究万象洞石笋提出的"中国8 200阶段"吻合,表明中国北方地区的8.2 ka事件是阶段性的事件,而南方的石笋氧同位素记录揭示的8.2 ka事件并未表现出阶段性特征,其原因有待于更多北方高精度石笋记录来进一步研究。LM2石笋氧同位素记录进行功率谱分析发现:在短尺度上季风变化与太阳活动密切相关,这与近年来对早全新世极端气候变化研究的驱动机制是一致的,早全新世亚洲季风的演化与太阳活动变化引起的太阳辐射能量的变化和北半球高纬气候的变化状况有关。

Based on 8 U / Th dates,449 oxygen and carbon isotopic data from stalagmite LM2 from Laomu Cave,West Henan Province,China,a record of the Asian monsoon inter- decadal resolution sequence during 8. 2 ~ 10. 9ka B. P. was established. The minimum δ18O value is-12‰,the maximum value is-8. 2‰ and the vibration amplitude reaches 3. 8‰. In the 10. 13 ~ 10. 9 ka B. P. sessions of early Holocene,the stalagmites in Jiuxian Cave,Laomu Cave and Dongshiya Cave reveals that monsoon stable in the period,but the stalagmites of Yamen Cave and Sanbao Cave in the southern China,polar ice cores GRIP record monsoon gradually. Differences of monsoon process of evolution between north and south China in the period may be related to climate response mechanism on the North and South China. Stalagmites LM2 recorded 8. 2 ka,9. 5 ka,10. 2 ka and 10. 9 ka weak monsoon event. Comparisons of LM2 to previously published early Holocene records show significant phase differences. The record of 9. 3 ka weak monsoon event is not obvious in LM-2 stalagmite δ18O curve,but it recorded a weak monsoon event in 9. 3 ~ 9. 6 ka B. P. and similar to DSY09( 2009),Y1,HS-4 record. This indicated there was a weakening monsoon event in this time. The complexity oxygen isotope transport make it the different performance in north and south. In addition,LM2 stalagmite records the beginning of 8. 2 ka B. P.,the oxygen isotope curve showing a decline stage,and luffing up to3 ‰,with Zhang et al proposing China ' 8200 phase' agreement by studying similar Wanxiang Cave. Northern China stalagmite showed the 8. 2 ka cold event was staged event,while the south records revealed no showing phase characteristics,the reason for this need to more northern precision stalagmite records for further studying. The LM2 correlate within errors with Greenland ice core records,illustrating Asian monsoon and the North Atlantic climate change have fast atmospheric transmission. The stalagmite in Laomu Cave record confirms earlier work that suggested that Asia Monsoon is closely related to solar activity. Early Holocene Asian monsoon related with changing in solar radiation energy and climate condition on the high northern latitudes.