近7000年巢湖沉积物环境磁学特征及其指示的亚洲季风变化  

MAGNETIC PROPERTIES OF SEDIMENTS FROM THE CHAOHU LAKE FOR THE LAST 7000 YEARS AND THEIR IMPLICATIONS FOR THE EVOLUTION OF ASIAN MONSOON

作　　者：张卫国[1] 戴雪荣[2] 张福瑞[2] 师育新[2] 俞立中[1] J.A.Dearing 

机构地区：[1]华东师范大学河口海岸学国家重点实验室,上海200062 [2]华东师范大学地理系,上海200062 [3]Department of Geography,University of Liverpool

出　　处：《第四纪研究》2007年第6期1053-1062,共10页Quaternary Sciences

基　　金：国家自然科学基金项目(批准号:40271107)资助

摘　　要：利用巢湖ACN钻孔,通过多参数磁性测量、粒度和AMS14C测年分析,探讨了近7000年以来巢湖沉积物磁性特征变化及其控制因素,并进而探讨了其对亚洲季风变化的指示意义。研究结果表明,ACN钻孔磁性特征由磁铁矿主导,其变化主要受沉积动力环境控制,间接反映了流域降水的变化。总体上粘土含量高的沉积物中磁性矿物含量较低、颗粒较细,形成于高湖泊水位环境,对应了降水量高的时期;而>32μm组分含量高的沉积物磁性较强、颗粒较粗,形成于低湖泊水位环境,对应了降水量低的时期。巢湖ACN的磁性记录(尤其是ARM/和ARM/SIRM两个参数)揭示了近7000年以来巢湖流域降水具有减少的趋势,导致湖泊收缩和沉积物中磁性矿物颗粒变粗。在这一长期变化的基础上,还存在6000aB.P.,5500aB.P.和3800aB.P.附近的显著干旱事件。这一磁性记录与中国东部地区的石笋、湖泊等记录可以很好地对比,是亚洲季风演变的区域响应结果。The monsoon climate changes during the Holocene, a period characterized by civilization development, has a significant impact on the living environment of the human society, especially the alteration of drought and floods associated with the strength of the summer monsoon. A variety of medias, including lake, delta, and marine sediments, corals, loess, and stalagmite, have been used to reconstruct the evolution of the Holocene Asian monsoon. Due to the broad area of Asia and the regional variations in climate and human activities, a complete picture of the Asian monsoon would be only drawn based on data integrated from extensive regional studies. The Chaohu Lake is a large shallow fresh water lake in the lower reach of the Yangtze River. Its evolution history contains information as to the paleoclimate and plaeoenvironment of northern subtropical climate zone. However, high-resolution records of Holocene environmental changes in this region are rare. In this study, a drill core（ 16.5m in length）was obtained from the present coastal plain of the Chaohu Lake, Eastern China, which covers the period of the Holocene according to AMS ^14C dating. The top 800cm part of the core was used for multi-parameter rock magnetic and bulk particle size investigations, with the purpose to retrieve high-resolution information of Asian Monsoon evolution over the last 7000 years. The magnetic properties of core are dominated by magnetite grains. Sedimentation dynamics, which is largely controlled by precipitation, plays a significant role in the variations of magnetic properties in the lake sediments. In general, sediments with higher clay content are characterized by lower concentration of magnetic minerals and finer grain size, which are deposited in a period of higher lake level due to stronger rainfall and therefore stronger summer monsoon. In contrast, sediments with a higher fraction of 〉 32μm size display stronger magnetization and coarser grain size of magnetic minerals, which are formed in a period of lower lake level

关 键 词：环境磁学 沉积动力 降水 亚洲季风 全新世 巢湖 

分 类 号：P318.41[天文地球—固体地球物理学] P532[天文地球—地球物理学]