MIS5b以来西樵山主量地球化学元素记录的D/O旋回与古生物实证

D-O Cycle Climate Changes Inferred from Main Geochemical Elements in the Xiqiaoshan of South China since MIS5b and Paleontological Evidence

位于中国南亚热带的西樵剖面主要是一套大约MIS5b以来形成的湖沼相。根据对该剖面759个主要元素氧化物SiO2、Al2O3和TOFE(Fe2O3+FeO)含量分析结果并以Al2O3/SiO2比值作为考察"脱硅富铝"的气候代用指标,将西樵剖面MIS5b以来的主要元素波动划分出34.5个元素旋回"CY0—CY34"(其中CY0属于0.5个旋回),其平均变率—3.1 ka/旋回为千年尺度级别。通过对这些元素与气候的关系和古生物(孢粉和哺乳动物化石)指示的古生态的论证,认为气候旋回与这些元素旋回存在内在的因果关系,进而提出MIS5b以来该地曾发生过34.5个时期的寒冷与温暖即东亚冬季风与夏季风交替变化的千年尺度的气候旋回。研究表明,MIS5b以来这些旋回中的若干阶段与北半球高纬地区D/O事件存在很好的"遥相关",即在时间—气候性质上的变化节奏基本一致。这是首次在中国的南亚热带发现的MIS5b以来高分辨率的元素/气候波动,其意义在于它展现了自那时以来一个比较完整的D/O气候旋回在东亚大陆更南部区域的存在。表明,这个时代东亚季风旋回的发生、发展和演化,除了北半球冰量变化幅度的影响外,西太平洋暖池(温度与消长幅度)亦对其产生过重要的影响,其中夏季风时期对低纬地区的影响更加强烈。

The Xiqiao section located in the southern subtropical zone of China mainly comprises lacustrine facies formed since the Marine Isotope Stage 5b(MIS5b).For 759 samples from the Xiqiao section,analyses of the main element oxides Si O2,Al2O3 and TOFE(Fe2O3+FeO)content and the Al2O3/SiO2 ratio,as climate indicators,found that 34.5 cycles CY0-CY34(CY0 as 0.5 cycle)of fluctuations of the main elements have occurred since MIS5b at an average variability of 3.1 ka/cycle,which represents millennial-scale climate change.By means of the relationships between the main elements and changes of climate,and the paleoecology from paleontological evidence(spore and mammalian fossils),it is believed that there is a causal relationship between the climate changes and these element cycles,and it suggests that the study area has experienced 34.5 periods of cold-warm millennial-scale climate change in the alternation of the East Asian winter and summer monsoons since MIS5b.The study shows that several periods within these cycles since MIS5b correlate well with Dansgaard-Oeschger(D-O)events in the high latitudes of the northern hemisphere,being basically the same in terms of time and characteristics.This is the first time that high-resolution climate fluctuation records of main elements since MIS5b has been discovered in the southern subtropics of China,which suggests that relatively complete D-O climate cycles take place in the southern East Asian continent.It also probably indicates that the occurrence,development and evolution of cyclic changes in the East Asian monsoon were once greatly affected by the Western Pacific warm pool(increasing and decreasing temperature and amplitude),in addition to the influence of the variation in the ice volume in the northern hemisphere,during which it affected the low latitudes even more intensely during the summer monsoon period.