【作者】 吴永红；

【导师】 郑祥民；

【作者基本信息】 华东师范大学 ， 第四纪地质学， 2012， 博士

【摘要】 古环境研究是认识人类现存环境的主要途径之一,而重建与人类现存环境相近的温暖气候阶段环境特征越来越得到更多的重视。全新世是现代人类进化最重要的时期,其气候变化特征与现存环境最为相似,所以对其气候特征的研究已经成为古环境研究的焦点。全新世气候变化的主要特征表现为末次冰期以来的快速转暖,但不同区域由于其特殊的地理环境特点,致使全新世的气候研究都带有区域分异的烙印。通过不同区域气候特征的对比研究,可以揭示各种自然地理要素之间影响耦合关系,如局地大气环流模式,地形地势差异引起的环境变化,青藏高原隆升造成的世界大气环流模式变化对中国局地大气循环产生的影响等,从而发现其中更为准确详细的变化,探索其内部机制。亚洲季风系统在全球水文及能量循环中扮演着非常重要的角色,它直接影响着南亚、东南亚及周边地区的气候环境特征,特别是青藏高原的隆升,使得该区域以及全球大气环流都变得更加复杂。长江三角洲位于太平洋西岸,亚洲大陆东缘,处于东亚季风影响范围内,有着典型的季风气候特征。长江三角洲沉积物特征很好的记录着全新世亚洲东南季风的发展变化旋回,通过对长江三角洲南翼平原PJ钻孔及太湖北部TH-004钻孔沉积物的分析研究,重建该区域全新世气候变化及东亚季风旋回特征。全新世期间,东亚季风经历了两次大幅度加强阶段,在PJ钻孔研究中,表现为8800～5400cal yr BP.2800～1200cal yr BP的温暖期,而在TH-004钻孔研究中表现为8000～7000cal yr BP及2600cal yr BP～1200aA.D.的气候暖湿阶段。贵州草海地区环境演变主要受印度洋季风的强弱转换和空间变迁的控制,草海NT泥炭沉积记录了近11800cal yr BP以来该区域气候环境变化特征,据此推测末次冰期晚期以来印度洋季风的变化旋回。印度洋季风季风在11800cal yr BP以来有两个阶段的强盛期,从11800cal yr BP加强,到9000cal yr BP左右开始快速减弱。在6500cal yr BP左右,季风再一次明显加强,最盛期在5000cal yr BP左右,之后开始缓慢减弱,一直持续到2000cal yr BP左右,2000cal yr BP之后季风强度大幅度减弱。在千年尺度的气候旋回上,有着多次快速的突变寒冷气候事件,这些突变寒冷气候事件在TH-004钻孔研究以及PJ钻孔研究中有着较好的对应性。在贵州草海NT泥炭沉积研究中,多次突变寒冷事件分别在1200、2600、4300、5800、6800、7600及8130cal yr BP左右,与PJ钻孔、TH-004钻孔研究结果有着较好的对应性。而且这些突变气候事件与董哥洞石笋氧同位素变化记录以及北大西洋气候变化有着很好的相关性。从以上结果得知,亚洲西南季风要比东南季风的加强提前约3000～4000calyr BP,本文认为这可能是由于东南季风与西南季风的推进与退缩的驱动因素有一致性(热带辐合带的南北移动),但由于东南季风与西南季风形成机理的不同,使其旋回特征具有不同步性。西南季风的形成是由于南半球东南信风越过赤道后在科里奥力作用下转而成为西南风,形成了影响我国的西南季风,当热带辐合带向北移动时,西南季风随之增强,能够携带大量的印度洋水汽影响我国西南地区。而东南季风的形成是由于海陆热力差异导致,当热带辐合带向北移动时,北半球接受更多的太阳辐射能量,太平洋表面温度有增加的趋势,但由于海洋巨大的热容,使得这一过程要延后几千年。同时由于北半球冰盖及末次冰期较低的大气CO2浓度的影响,也有效地延迟了东亚季风的加强,但是这些因素对西南季风却没有很大影响。另一方面,海平面升高以及青藏高原夏季热源冬季冷源的效应也很大程度上促进了印度洋夏季风的加强。由于以上诸方面的影响,致使热带辐合带向北移动时,西南季风能够很快作出响应,而东南季风要滞后几千年才能做出响应；相反,热带辐合带向南移动时,西南季风与东南季风都有退缩的趋势,但东南季风要滞后几千年。但由于二者的变化都受到热带辐合带南北移动的控制,使得西南季风区与东部季风区全新世气候变化表现出相似的“双峰型”变化特征,也就是全新世期间亚洲季风可能经历两次大范围的加强。而在突变气候事件方面,长江三角洲PJ钻孔、TH-004钻孔及贵州草海NT泥炭沉积物研究揭示的全新世突变气候事件与北大西洋气候及全球其它地区研究成果有着很好的可比性,我们认为,能够在全球范围内引起这些突变气候事件的同步性发生,可能是由于全球性气候因子的周期性变化导致,而并非热带辐合带的南北移动引起的季风变化或者其它区域性气候因子变化引起。更多还原

【Abstract】 The study of paleoenvironment is the main way of understanding of present environment, and paleoenvironment reconstruction during the warm climate phase which is similar to the present environment draws more and more attention. Holocene is the most important period of modern human evolution, and characteristics of Holocene climate is most similar with the present environment. So, the study of characteristics of Holocene climate change has become the focus of paleoenvironment researches. The Holocene climate change is characterized by the rapid warming since the last glacial, but each region has its an unique geographical environment characteristics, leading to the results of Holocene climate research with the imprints of regional differentiation. By the contrast research between the regional and another, we can uncover the influence and relationship of mutual coupling between the various physical geographical factors, such as local atmospheric circulation model, environmental changes being caused by the differences in topography and the atmospheric circulation changes of the world that was influenced by Qinghai-Tibet Plateau uplift which affect Chinese local atmospheric circulation. Thus we can reveal that subtle changes of the various physical geographical factors, and explore its internal mechanisms.The Asian monsoon is an important component of atmospheric circulation and plays a significant role in the global hydrologic and energy cycles. It directly affects the features of climate and environment in South Asia, Southeast Asia and the surrounding areas. Especially, the uplift of the Qinghai-Tibet Plateau makes the regional and global atmospheric circulation become more complex. Yangtze River Delta is located in the west coast of the Pacific Ocean and east of the Asian Continent, within the sphere of the East Asian monsoon, has a typical monsoon climate characteristic. The changes of the strength of the monsoon circulation is caused by changes of solar radiation in the northern hemisphere. Analysis of sediment characteristics of the Yangtze River Delta can be a good instruction of the cycle characteristics of the East Asian monsoon in Holocene. Depending on analyses of core P J in southern wing of the Yangtze River Delta and core TH-004in the northern area of Taihu Lake, we try to reconstruct the characteristics of Holocene climate change in this region and the cycle characteristics of the East Asian monsoon. During the Holocene, the East Asian monsoon has experienced two significant fluctuations. In the study of core PJ, there are two warm periods in the8800～5400cal yr BP,2800～1200cal yr BP, and in the study of core TH-004, two warm and humid climate phases in the8000～7000cal yr BP and2600cal yr BP～1200a A.D..The regional environment evolution of Caohai in Guizhou is mainly affected by the changes of the strength and spatial conversion of the Indian Ocean monsoon. Analysis of NT peat sediment of Caohai can be a good instruction of the characteristics of climate change in the region since11800cal yr BP, and based on it we can infer the cycle characteristics of the Asian southwest monsoon since the late glacial. Overall, there are two powerful periods of the Asian southwest monsoon since11800cal yr BP. The southwest monsoon began to strengthen since11800cal yr BP, and decreased quickly about9000cal yr BP. The second significantly powerful period of the southwest monsoon began around6500cal yr BP, the most peak is around5000cal yr BP, and began to weaken until around2000cal yr BP.In millennial-scale climate cycles, there are a number of rapid mutation climate events. These mutations cold climate events has a perfect correlation between the study of TH-004core and PJ core. In the study of NT peat sediment in Caohai Guizhou, there are a number of rapid mutation climate events around1200,2600, 4300,5800,6800,7600and8130cal yr BP. The time of occurrence of these mutations climate events have a perfect correlation with changes of oxygen isotope of stalagmite in the Dongge cave and climate change in the North Atlantic.These results suggest that the Asian southwest monsoon strengthened than the southeast monsoon in advance about3000-4000cal yr BP. This paper argue that it may be caused by the consistency of the drivers of the Asian southwest monsoon and the southeast monsoon (north-south movement of intertropical convergence zone (ITCZ)), however, the formation mechanism of the Asian southeast monsoon and southwest monsoon is different, making their asynchronous of strengthening of the monsoon. The southwest monsoon, when southeast trade winds of the southern hemisphere across the equator by the Coriolis force, turns into a southwest wind, and forms the southwest monsoon that has an influence on the climate of the southwest China. When the ITCZ move to the north, the Asian southwest monsoon enhances and be able to carry a lot of water vapor from the Indian Ocean to southwest China. The Asian southeast monsoon is due to the sea-land thermodynamic contrast. When the ITCZ move to the north, the northern hemisphere receive more solar radiation energy, the Pacific Ocean surface temperature has an increasing trend, but because of the huge heat tolerance of ocean, making it should be delayed for thousands of years. And possibly the remnant Northern Hemisphere ice sheets and the lowered concentration of carbon dioxide in the atmosphere during the last glaciation that delayed the development of the East Asian monsoon, but had less influence on the tropical Indian monsoon. On the other hand, the signficant rising of sea level during deglaciation and the progressive warming of the high Qinghai-Xizang Plateau, both are favorable for the development of the Indian Ocean summer monsoon. Due to the impact of the above factors, when the ITCZ move northward, the Asian southwest monsoon can quickly respond to it, but strengthening of the southeast monsoon lags thousands of years. On the contrary, when the ITCZ move southward, the Asian southwest monsoon and the southeast monsoon has the trend of shrinking, but southeast monsoon lags thousands of years. However, changes of the Asian southwest monsoon and the southeast monsoon are controlled by north-south moving of the ITCZ. So, Holocene climate chang of the Asian southwest monsoon region and the southeast monsoon region showed similar changes characteristics. That is, the Asian monsoon may experience two large-scale strengthening during Holocene.Mutation climate events recorded in the PJ core in the Yangtze River Delta, the TH-004core in Taihu lake, and the NT peat sediments of Caohai Guizhou are supported by eviences from the Norhte Atalntic, Indian Ocean, and West Pacific Ocean. We thus believe that these climate events can be regarded as synchronization worldwide, and that they may be caused by cyclical changes of global climate factors, rather than regional climatic factors such as monsoon changes due to north-south shift of the ITCZ.更多还原