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学科主题: 地理学
题名: 青藏高原纳木错湖泊沉积物正构烷烃与环境变化研究
作者: 林晓
答辩日期: 2008-06-29
导师: 朱立平
专业: 自然地理学
授予单位: 中国科学院研究生院
授予地点: 北京
学位: 博士
关键词: 青藏高原 ;  湖泊沉积 ;  纳木错 ;  正构烷烃 ;  环境变化
索取号: B000008
部门归属: 图书馆
摘要: 青藏高原是全球地学界瞩目的焦点,常被科学家们称为地球的第三极。青藏高原的湖泊面积占全国的50%左右,而纳木错作为青藏高原的第二大湖泊,具有非常重要的地位。本论文利用纳木错深水湖芯的正构烷烃重建了该区域8.4kaBP以来的气候环境变化历史,是973项目“青藏高原环境变化及其对全球变化的响应与适应对策”之子课题“青藏高原过去环境变化的时空特征(2005CB422002)”的研究内容之一。生物标志物在高原湖泊沉积与环境变化中的应用还不多见,本研究选取了结构简单、具有饱和性和稳定性的正构烷烃作为研究对象。首先利用GC/MS测试了纳木错周边植物及表层沉积物所含烷烃的组成与含量。测试结果表明:沉水植物主要含有C21、C23、C25等中等链长烷烃;陆生高等植物主要含有C27、C29、C31、C33等长链烷烃,其中C29多来自于木本植物,C31多来自于草本植物,C33则专属于香柏。据此,可推断纳木错表层沉积物中正构烷烃的来源以陆生植被输入为主,沉水草本植物输入次之,低等藻类输入最少。并且这些烷烃在空间分布上有所差异:长链烷烃由陆生高等植物输入,因而从湖岸到湖中心,其相对丰度会逐渐降低;而中等链长烷烃由沉水植物输入,这种空间变化并不明显;短链烷烃则完全没有空间差异。然后利用GC/MS进一步测试了纳木错深水湖芯NMLC-1孔沉积物中的烷烃组分及含量。分析结果表明其来源仍以高等植物输入为主,与表层沉积物有所不同的是,在1.4kaBP以前,沉水植物输入的烷烃明显超过陆生植物。各类烷烃具有不同的环境意义,陆生植物输入的长链烷烃能反映温度和降水强度的变化,沉水植物输入的中等链长烷烃能反映温度和湖面波动的变化。而整个序列中短链烷烃始终较少,并且由于“优先”降解作用和湖泊营养条件的限制,它们保存的环境变化信息相当少,没有明确的环境意义。在此基础上,根据该孔烷烃含量变化重建了纳木错8.4kaBP以来的环境变化序列:约8.4~6.7kaBP期间,气候温干,湖面较低,降水强度变化易引起湖面波动。约6.7~2.9kaBP期间,早期温暖湿润,陆生和沉水植物繁盛;晚期降温,逐渐干旱,以冷干事件结束。约2.9kaBP~现在,冷暖交替,中期出现冰川融水的大量补给,1.4ka以来趋于干旱。将烷烃与其它成熟的环境代用指标进行比较和验证,确定中长链烷烃比较真实地反映了过去环境变化,在湖泊沉积环境重建研究中具有实际应用的意义。与其它湖泊环境变化序列的对比的结果表明:纳木错的暖期环境主要受季风增强的影响,冷期环境主要受西风环流的影响;有时也受到冰川作用的影响。同时也说明纳木错区域的环境变化特征具有明显的过渡性。
英文摘要: Tibetan Plateau is always focused by geoscientists and often called “The Third Pole” of the earth. The area of lakes on Tibetan Plateau is about 50% of whole country’s. As the second largest lake on Tibetan Plateau, Nam Co is very important to research in the field of past global changes. In this thesis, the environmental changes of Nam Co region since 8.4kaB.P. were reconstructed by n-alkanes in lake sediments and other environmental indicators. These research are supported by project of “Spatial and Temporal Characteristics of Past Environmental Changes on Tibetan Plateau (No. 2005CB422002)”, which is the sub-project of National Basic Research Program of China (Responses of Environmental Changes on the Tibetan Plateau and adaptations under the Global Changes). Applications of biomarkers in plateau lake sediments to palaeoenvironmental reconstruction is not abroad now. Because n-alkane has a simple carbon skeleton with saturation and stability, it was looked as a research object. Based on the measure of n-alkanes extracted from plants, it has been known that the n-alkane distribution of submerged aquatic plants commonly maximize at n-C21, C23, and C25 alkanes. Land vascular plants contain large proportions of n-C27, C29, C31and C33 alkanes in their epicuticular wax. In addition, n- C29 and n-C31 alkanes come mainly from woody plants and herbaceous plants, respectively. n-C31 alkanes come mainly from Sabina pingii. According to this result, the main resources of n-alkanes in Nam Co surface sediments are not phytoplankton but land plants and submerged aquatic plants. Furthermore, abundance of long chain length n-alkanes come from land vascular plants decreased gradually from lakeshore to center. But difference of spatial distribution of mid chain length n-alkanes come from submerged aquatic plants is not obvious enough. Especially the short chain length n-alkanes come from phytoplankton distribute evenly in the lake. Based on the measure of n-alkanes extracted from NMLC-1 core sediments of Nam Co, it can be decided that main resource of them is still higher plant vascular plants. But mid chain length n-alkanes are more abundant than long chain length n-alkanes before 1.4kaB.P.. Different kind of n-alkane has different environmental significance. Temperature fluctuation and precipitation intensity can be reflected by concentration changes of long chain length n-alkanes, while temperature fluctuation and water level changes can be reflected by mid chain length n-alkanes. But short chain length n-alkanes are not suitable for environment reconstruction because they are easily degenerated by bacteria and forbidden by TN. Then palaeoenvironmental changes of Nam Co region was reconstructed by n-alkanes in core sediments. The results indicated that in the period of 8.4~6.7 kaB.P., it was warm and the precipitation slightly increased. This stage was ended by an obvious cold/dry event. During 6.7~5.8 kaB.P., temperature increased rapidly. At about 6.0 kaB.P., it was again in the condition of warm and wet and very optimum to the growth of land plants and submerged hydrophytes. After that, temperature decreased smoothly. The environmental conditions of Nam Co shifted back to cold and dry at 3.0 kaB.P.. From 2.9 kaB.P. to now, it was fluctuated between warm and cool, and became arid after 1.4 kaB.P.. It can be proved that environmental changes reflected by n-alkane is credible through comparison with other well-known environment indicators. N-alkanes has application significance in the field of research on environment reconstruction by lake sediments. Based on the comparison of environment sequences between Nam Co and other lakes on Tibetan Plateau, Nam Co would influenced by strong monsoon and westerly circulation in warm stage and cold stage, respectively. So the environmental change in the region of Nam Co has a transitional character.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.itpcas.ac.cn/handle/131C11/1258
Appears in Collections:图书馆_学位论文

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Recommended Citation:
林晓.青藏高原纳木错湖泊沉积物正构烷烃与环境变化研究[博士].北京.中国科学院研究生院.2008
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