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学科主题: 地理学::自然地理学
题名: 藏东南然乌湖现代沉积过程及其环境变化研究
作者: 甄晓林
答辩日期: 2009-06-03
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: 藏东南 ;  然乌湖 ;  现代沉积 ;  空间分布 ;  环境变化
索取号: S000019
部门归属: 图书馆
摘要: IPCC报告指出近年来全球变暖的趋势越来越明显,青藏高原作为地球的第三极,其对全球变暖的响应越来越受到全球地学界的关注。藏东南地区的然乌湖为外流湖泊,主要补给来源于周边发育的海洋性冰川,对然乌湖现代沉积过程的研究将有利于了解该区域的环境变化特点,以及湖泊对全球变暖导致的冰川变化的响应。然乌湖坐落在雅鲁藏布江支流帕隆藏布的源头,湖泊按形态分为上湖雅错、中湖安错和下湖安目错,由于特殊的湖泊形态,使得湖泊现代沉积过程在不同湖区的空间分布不同。(1)通过对然乌湖基础水深的测量和监测发现,雅错平均水深为18.6m,安错平均水深为11.2m,安目错平均水深为10.6m,湖水深度与温度变化一致,其中在6-9月份水深较深。(2)通过对然乌湖流域水化学的分析发现,河水和湖水中的主要阴阳离子一致,分别为(HCO3-+CO32-)和Ca2+,通过Gibbs图解分析发现离子主要来源于岩石风化,说明流域土壤影响了水体离子成分。在垂直剖面上,随水温的降低,溶解氧饱和度逐渐降低;由于湖水比较浑浊,PAR在水深1m左右几乎为零;受水体浮游生物等因素的影响,pH、TDS和溶解氧的变化相对复杂;而在横剖面上各个参数的变化一致,表明湖水的混匀程度较高。(3)通过对然乌湖沉积物的粒度特征分析得出,从上湖雅错到下湖安目错,平均粒径表现为逐渐变细的趋势,而且在河流冲积扇位置的粒度较粗,反映出然乌湖是以河流为主要动力的湖泊沉积过程。对土壤粒度的分析发现,受植被覆盖条件的影响,然乌湖西南侧山上的土壤粒度比东北侧山上的细。进一步与湖泊沉积物的粒度指标对比发现,土壤中的粗颗粒物质较多,而沉积物中的细颗粒物质较多。(4)通过对理化指标(包括粘土矿物、TOC以及化学元素)的分析得出,然乌湖主要的粘土矿物类型为伊利石,揭示湖区主要受冷湿风化作用的影响。受湖泊内生浮游生物的生境条件的影响,TOC在不同湖区的分布不同,其中安目错的沉积物中TOC含量最高。而沉积物中的常量与微量化学元素分布与沉积物的粒径有关,其中Ca、Mg等元素分布与砂含量相关,而Rb、Cs等元素分布与粘土成分有关。稀土元素的球粒陨石标准化分布模式表明,河流与湖泊沉积物中稀土元素变化与上地壳的变化一致,均表现为轻稀土元素相对重稀土元素富集,并存在明显的Eu亏损和轻度的Ce富集。(5)对然乌湖长岩芯的14C定年分析发现,然乌湖的形成及其演化过程可能开始于末次冰后期,且存在几次溃堤事件。以短岩芯RW07-7的210Pb和137Cs精确定年结果为基础,多指标的分析结果显示,平均粒径、TOC指标与波密的器测温度资料变化较一致,基本可以用来代表温度的序列变化,并相应解释了其他指标变化的可能原因,最后通过建立方程探讨了各指标与温度之间的定量关系。
英文摘要: IPCC report points out that global warming is becoming more evident in recent years. As the third Pole of Earth, Tibetan Plateau’s response to global warming attracts more and more attention from geoscientists. Ranwu lake is one of outflow lakes in southeast of Tibetan Plateau and its water source mainly comes from the maritime glaciers. Study on modern sedimentary processes of Ranwu lake will be beneficial to understanding the characteristics of regional environmental change and the lake response to the glaciers change resulted by global warming. Ranwu lake is located in the headstream of Prulung TsangPo river which is a tributary of Brahmaputra. It consists of Ya Co, An Co and Anmu Co which are located in the upper, middle and lower area of Ranwu lake respectively. Because of the special shape of Ranwu lake, the modern sedimentary processes are different among Ya co, An Co and Ammu Co. (1) Through investigating and monitoring water depth of Ranwu lake, it was found the depths of Ya Co, An Co and Anmu Co were 18.6, 11.2 and 10.6 meters respectively. The water depth changes were consistent with the temperature change, and the water depth was relatively deeper from June to September. (2) The analysis of water chemistry of different water bodies in Ranwu basin showed that there were similar main ions in river water and lake water. The main cation was Ca2+ and the main anion was (HCO3-+CO32-). Gibbs diagram showed that the ions were derived from weathering of rocks. Analysis of soil properties indicated that soil infected the ion composition of lake and river. In vertical water profiles of Ranwu lake, the changes of parameters were different. For example, LDO% decreased as water temperature decreased, and PAR was almost zero at the depth of 1m due to the turbid water. As a result of impact of some reasons such as water planktons, the changes of pH, TDS and LDO were very complicated. However, all the parameters had similar changes in the cross water profiles of Ranwu lake, which showed that the water mix was in a higher degree. (3) Through analyzing the grain size of lake sediments, it was found that the mean size became finer from Ya Co to Anmu Co, and it was much coarser in river alluvial fan, which meant that river was the key power for the lake sediments processes of Ranwu lake. Because of the effect of vegetation cover, the grain size of hill soil in southwest of Ranwu lake was finer than that of northeast hill. Compared with the parameters of grain size in lake sediments, it was showed that there were more coarse grains in soil, but there were finer grains in lake sediments. (4) Analysis of the physical and chemical proxies includes clay minerals total organic carbon (TOC) and geochemical elements. The main type of clay minerals was illite, which indicated that those lake regions were mainly affected by cold wet weathering impact. By the impact of planktons’ habitat conditions, the distributions of TOC were different among Ya Co, An Co and Anmu Co. The highest TOC of lake sediments was in Ya Co. However, the major and trace elements both had good relationships with the grain size. For example, Ca and Mg were related to sand distribution, but Rb and Cs were related to clay distribution. The results of rare earth elements (REE) showed that river and lake sediments had the same changes with the upper continental crust (UCC). In chondrite-normalized REE distribution pattern, light REE were more enriched than heavy REE, and there was obvious loss of Eu element and slight enrichment of Ce element. (5) The results of long cores 14C dating indicated that the formation and evolution of Ranwu lake might begin from the last post-glacial, and there were several breach events in the history of Ranwu lake. Based on the dating result of RW07-7 short core by 210Pb and 137Cs, it was found that the changes of mean grain size and TOC proxies were identical with Bomi temperature. Therefore they could represent temperature changes in time series and explained the possible reasons for other proxies’ changes. The quantitative relationships between temperature and proxies were discussed basing on the equations.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.itpcas.ac.cn/handle/131C11/1235
Appears in Collections:图书馆_学位论文

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Recommended Citation:
甄晓林.藏东南然乌湖现代沉积过程及其环境变化研究[博士].北京.中国科学院研究生院.2009
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