|Place of Conferral||北京|
|Keyword||青藏高原 湖泊沉积 纳木错 正构烷烃 环境变化|
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.
|MOST Discipline Catalogue||理学::地理学|
|Table of Contents|
|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[D]. 北京. 中国科学院研究生院,2008.|
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