【作者】 隆浩；

【导师】 王乃昂；

【作者基本信息】 兰州大学 ， 自然地理学， 2006， 硕士

【摘要】 季风边缘区对气候变化比较敏感,是过去全球变化研究的理想场所。中国学术界对季风边缘区全新世气候变化研究颇多,但分歧较大,尤其是全新世中期的气候状况一直是古气候学家争论的焦点。传统的观点认为,中国的全新世中期气候温暖湿润,而最近的研究表明中全新世季风边缘区存在千年尺度的干旱事件。因此,中国季风边缘区全新世中期是温暖湿润还是干旱甚至寒冷时期,是一个值得学术界探讨的重要科学问题。为此我们选择了位于季风边缘区的石羊河终端湖泊（ZYC剖面）和毛乌素北缘的泊江海子湖泊（PJHZ剖面）作为研究对象,通过对两个区域的湖泊沉积学、地球化学、第四纪年代学和湖泊地貌学分析,重建了季风边缘区全新世中期的环境演化历史,并对气候变化韵律和驱动机制进行了探讨。主要结论如下: 1.已有的研究表明,泥炭有机质的碳库效应是比较小的,而湖相淤泥和螺壳在湖泊中都存在一定的碳库效应。根据测年结果（第三章）我们发现同一层位（如QTL剖面315cm）的泥炭有机质的常规¹⁴C测年结果和螺壳AMS测年结果几乎相同,QTL剖面425cm层位湖相淤泥和螺壳测年也显示了相同的结果,其差异完全在误差范围之内,据此我们认为该区域碳库效应较小,两个实验室的测年结果是比较可信的。 2.季风边缘区9～3Cal kaB.P.的气候变化历史可划分为4个阶段:9Cal kaB.P.到7.8Cal kaB.P.期间,气候类型属于湿润背景下的转暖过程,植被状况好转:而在7.8～7.5Cal kaB.P.出现了显著的百年尺度的干旱事件,沉积物主要以砂质沉积为主,此时湖泊生产力显著下降,与石羊河中游地区对比发现此干旱事件具有区域性;湖泊沉积学和地貌学证据表明全新世最为暖湿的气候适宜期出现在7.5～5Cal kaB.P.,此阶段气候是整个全新世期间最为暖湿的,水热状况良好;5～3Cal kaB.P.以来,区域出现了较为明显的干旱化趋势,且这一结论也得到了湖泊地貌学和年代学证据的支持。 3.对气候代用指标数据的小波分析表明C/N、TOC、δ¹³C、CaCO₃序列的512a、900～1100a的振荡周期非常显著,并通过了99%红噪声（red noise）检验。更多还原

【Abstract】 The East Asian monsoon margin areas of China are very profit to study the past global environment change because of their sensitivities to the climate changes. Therefore, these areas received intensive attention from paleoclimatologists in recent years. There are a large number of researches on the Holocene climatic variabilities in these areas as yet, but quite different opinions have been expressed as to the climatic conditions of Mid-holocene. Traditionally, the Mid-holocene in most parts of China was thought to be warmer with higher precipitation, resulting from a strong Asian summer monsoon. However, some recent researches have proposed a Mid-holocene drought interval of millennial-scale in East Asian monsoon margin areas. Thus whether Mid-holocene was dry or humid remains an open issue. In this paper, the Mid-holocene （9³Cal kaBP） climate variations and rhythm are reconstructed on the basis of sedimentological and geomorphological data recovered from two series of well-dated lake records. According to the study, we come to some conclusions as follows:1. According to the principle and technology of ¹⁴C dating, researchers found that the reservoir effect on radiocarbon ages is different between peat material and mollusk shells or inorganic carbon in the lake. Dating results of ZYC and QTL section indicate the ages of peat material are almost equal to those of mollusk shells at depth 315cm and 425cm, measured in Chronology Laboratory of Lanzhou University and Chronology laboratory of Peking University, respectively. Accordingly, it seems that reservoir effects of the research region are not evident. Hence the dating results are reliable.2. Based on the reconstruction with multi-proxy records and well-dated data, the climate evolution in the East Asian monsoon margin areas during 9-3 Cal kaBP is divided into four stages: ①from cold and dry to warm and humid during the period of 9⁷.8Cal kaBP. ②a significant drought interval of multicentennial scalebetween 7.8-7.5 Cal kaBP. ?Holocene optimum characterized by a warm and moist climate during the period of 7.5⁵Cal kaBP. ?from humid to dry during 5³Cal kaBP.3. Wavelet spectral analysis of C/N^ TOC\ 8I3C\ CaCO3 records of QTL section shows that statistically significant multicentennial and millennial periodicities centered on 512 and 1000 years, which are close to the significant periodicities of residual A14C （reflecting solar activity）. These results indicate there is a close relation between climate change of East Asia monsoon margin areas and solar activity. It was supported by the suggestion that climate change in East Asia monsoon margin areas is probably mainly driven by solar activity with two dominant periodicities—512a and 1000a, which was proposed in more and more relative researches.更多还原