【作者】 赵爽；

【导师】 夏敦胜； 靳鹤龄；

【作者基本信息】 兰州大学 ， 自然地理学， 2013， 硕士

【摘要】 在全球变暖背景下,气候变化的趋势和规律是当今社会和学术界关注的热点问题。全新世是人类社会迅速发展的关键时期,全新世气候变化研究是预测未来人类生存环境演变的主要依据之一,因而备受学术界的重视。科尔沁沙地位于现代东亚季风影响的边缘地带,生态环境脆弱,对气候变化反应敏感,是气候变化研究的理想区域。本研究通过对科尔沁沙地东北缘的六户屯风成沉积剖面进行粒度、CaCO3含量、有机质含量和环境磁学参数的系统分析,选取适宜的气候代用指标,在精确定年的基础上,恢复和重建了科尔沁地区4300～1000cal a BP气候演化历史。在高分辨率气候记录的支持下,通过与西辽河流域古文化演变序列及黄河流域朝代变迁的对比,详细论述了气候变化与古文明演化的关系。主要得出以下结论：科尔沁地区4300～1000cal a BP的气候演化主要经历了以下三个阶段：4300～3800cal a BP为暖湿气候期,是研究区气候最暖湿的时期,可能对应于全新世大暖期末期阶段,且暖湿程度有不断降低的趋势,至3800cal a BP时气候已经相对比较冷干,暗示气候适宜期在此时终结；3800～1700cal a BP为冷干气候期,其中3000cal a BP为气候演变的节点,前期冬季风不断增强,夏季风不断减弱,气候由暖湿逐步向冷干过渡,后期冬季风持续强盛,夏季风则逐渐恢复；1700～1000cal a BP为亚暖湿气候期,气候条件相对暖湿,但不及大暖期时期。在研究时段内,冬季风和夏季风大致呈反相位变化,且气候变化的总体趋势与中国东部季风区地质载体记录的亚洲季风演化历史基本一致。科尔沁地区晚全新世气候变化主要受太阳辐射的驱动,主要体现在：气候变化与太阳活动有相同的变化周期,且其长期趋势受太阳辐射轨道尺度变化的控制。气候变化对古文化有重要的影响,史前时期的文明演替和历史时期社会治乱、王朝盛衰都与气候变化有关。西辽河流域的文明演化主要受降水和温度的影响,冬季风对社会和文化的影响相对较弱。具体来说,小河沿文化向夏家店下层文化转变、夏家店下层文化向夏家店上层文化转变、夏家店上层文化衰亡并被中原文化取代、及历史时期南北朝时的游牧民族南侵(386～589AD)和唐朝中后期的衰落(755～907AD),均与夏季风衰退、温度降低造成的气候环境恶化有关；唐朝初期(618～755AD)的文化繁荣则与适宜的气候条件密不可分。不同的生产方式对气候条件有不同的要求,生产方式的转变和人口迁移是人类适应环境的变化的重要手段。在史前文明中,气候变化对生产方式的选择有重要的影响；在历史时期,政治和文化因素对人类生产生活的影响明显增大。随着社会的发展,人类对气候变化的适应能力增强。此外,环境磁学研究发现,科尔沁沙地沉积物中的磁性矿物含量较少,以磁铁矿为主导,还含有一定数量的赤铁矿,可能含有少量磁赤铁矿和/或针铁矿,且矿物组成比较稳定；磁性矿物粒度较细,以稳定单畴(SSD)和超顺磁(SP)颗粒为主,且磁粒度比较均一。磁性矿物的这种偏细的粒度分布,不可能完全是由成壤作用形成的,源区碎屑成因磁性矿物可能已经达到SSD粒级。磁粒度参数χARM/χlf和χARM/SIRM可以作为气候代用指标,而常用的磁化率参数在本研究中指示意义不明确。由于原生碎屑磁性矿物已经达到SSD粒级,χARM/χlf和χARM/SIRM与成壤作用表现为反相关。更多还原

【Abstract】 Under the background of global warming, the trends and regularities of climate change is one of the focuses of society and academic circles. Holocene is the key period of the development of human society, and Holocene climate change is one of the main bases to predict the future evolution of our living environment. The Horqin sandy land in the western part of northeast China is located in the present margin of East Asian Monsoon zone, and its landscape is sensitive to the climate change. This paper present a high-resolution climate evolution record during4300～1000cal a BP derived from sequential aeolian sediments of Liuhutun section in the northeastern frontier of the Horqin sandy land. The2.96-m sandy paleosol/sandy loess/fine sand section, with a chronological support of7radiocarbon dates, has been analyzed for grain size distribution, CaCO3content, organic matter content and environmental magnetic parameters. With support from high-resolution climate record, by comparing with ancient civilization development in the Western Liaohe River Basin and dynastic transitions in the middle and lower reaches of the Yellow River, the relationship between climate change and cultural development was discussed in detail.The results show that4300～3800cal a BP was the warmest and wettest epoch during the study period, with a trend of becoming cooler and drier. The Holocene Optimum in this region is supposed to end at3800cal a BP. Climate between3800and1700cal a BP was cold and dry, this period can be subdivided into two phases with3000cal a BP as a boundary. Climate became cooler and drier before3000cal a BP, afterwards the winter monsoon stayed at a strong level while the summer monsoon gradually strengthened.1700～1000cal a BP was a warm and humid period, but the climatic conditions were inferior to the Holocene Optimum. On the millennial scale, our records show an anti-correlation between the strength of summer and winter monsoon. The main trends of climate changes during this period can be compared with stalagmite δ18O records of the strength of summer monsoon in the south China. Late Holocene climate change in this region was mainly driven by solar radiation, on the one hand the long-term trend of climate change was controlled by solar radiation change in orbital scale, on the other hand the centennial scale cyclical fluctuation of the climate was driven by the solar cycle.Climate change is an important trigger of the ancient civilization transitions and dynastic changes. Precipitation and temperature play an important role in the cultural collapses in the Western Liaohe River Basin. Specifically, the collapses of Xiaoheyan, Lower Xiajiadian and Upper Xiajiadian culture, nomadic southward invasion during the Northern and Southern Dynasties, and the decline of Tang Dynasty, are related to the environmental degradation caused by precipitation and temperature decrease. Cultural prosperity in the early Tang Dynasty is inextricably linked with the suitable climatic conditions. Different modes of production have different requirements on the climatic conditions, thus, human adapt to environmental changes through the transformation of the production methods. In prehistoric civilizations, climate change had an important influence on the choice of the mode of production; in historical period, impact of political and cultural factors on the human society increased significantly. With the development of the society, human’s ability to adapt to climate change had enhanced obviously.Furthermore, detailed environmental magnetism researches show that there are only a few magnetic minerals in the aeolion sediments of Liuhutun section, contents mainly magnetite with few haematite, and perhaps maghaemite and/or goethite. The main magnetic grain sizes are in stable single domain (SSD) and superparamagnetic (SP) size fractions. Those fine-grained magnetic particals can’t be completely formed by pedogenesis, lithogenic magnetic minerals of source materials might be already in SSD size fractions. The relationship between magnetic susceptibility and environmental factors is complicated, while XARM/Xlf and XARM/SIRM, which denote magnetic grain size, can be used as paleoclimatic proxies. Because the aeolian magnetic particals are in SSD size fractions, XARM/Xlf and XARM/SIRM show an inverse correlation with pedogenesis, which are different from pedogenic mechanism of loess-paleosol sequences in the Chinese Loess Plateau.更多还原