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| 我国湖泊沉积物生物硅记录及其环境指示意义——以青海湖为典型案例 | |
| 其他题名 | Biogenic silica contents and the related environmental significance of lake sediments, and a case study at Lake Qinghai |
| 刘斌 | |
| 出版年 | 2014 |
| 学位类型 | 博士 |
| 导师 | 安芷生 ; 徐海 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 晚全新世的气候重建对人类预测未来气候具有重要意义，其中最近2000年来气候变化的研究尤为重要。因此越来越多的研究通过湖泊沉积物、冰芯、洞穴堆积物、泥炭、树轮等重建过去两千年的气候。 湖泊沉积物具有分辨率高、连续性好、代用指标丰富和分布广泛的特点，是过去气候变化研究的重要载体，已被广泛应用于过去两千年的气候重建。湖泊沉积记录中有众多物理、化学、生物指标，其中生物硅是一种被广泛应用的生物指标。 生物硅是一种来源于硅藻、放射虫和海绵骨针等硅质生物的无定形硅。生物硅的积累反映了生产力的时空变化，因此被作为古海洋学与古气候学研究中一种重要的替代指标。湖泊沉积物生物硅被认为是反映气候变化及生态响应的重要指标之一。但是，不同湖泊由于气候条件，流域植被覆盖，以及基岩等存在诸多的不同，其生物硅记录环境/气候变化的过程有所差异，生物硅指示的环境/气候意义也存在较大差异。因此，有必要调查不同湖泊生物硅变化的普遍规律，并选择一些典型湖泊系统开展生物硅记录环境/气候变化过程的研究，阐明生物硅指标的环境/气候意义。基于以上问题，本文主要分为以下两部分： 首先，本文选取我国东北、西北及西南地区的十个湖泊，调查了生物硅含量变化情况，并通过区域对比初步分析了生物硅含量变化的原因，试图寻找我国不同湖泊生物硅变化的一般规律。 其次，本文开展了典型湖泊生物硅环境意义及其记录研究。青海湖是我国最大的内陆湖泊，地处青藏高原东北缘，位于干旱/半干旱区过渡带，对气候变化十分敏感，是研究全球气候变化及其动力成因的理想场所。虽然前人对青海湖有较为详尽的研究，但青海湖沉积物生物硅及其环境/气候意义尚缺乏系统研究。因此本论文以青海湖最近约2000年的沉积岩芯为研究对象，开展了生物硅、粒度、磁化率、总有机碳等指标的综合研究，重建了研究区近2000年以来气候变化历史，并通过与冰芯、树轮等其他代用资料对比，探讨生物硅指标对气候变化的响应过程。 本论文获得以下初步成果和结论： （1） 通过对比发现西北地区湖泊生物硅含量平均值整体低于东北和西南地区湖泊，可能是由于西北地区较低的温度和较少的降水量导致硅藻生长受限造成生物硅含量较低。东北部湖泊与西南部湖泊生物硅含量均相对较高，但形成原因却不同。东北部两个湖泊均靠近人类聚居区，属富营养型湖泊，虽然东北地区年均温较低，但充足的营养盐为硅藻生长繁茂提供了必要因素。本研究涉及的西南地区湖泊大多为中贫营养型湖泊，他们生物硅含量较高主要归因于较高的温度和较多的降水。 （2） 对比了青海湖流域表土、河流沉积物和湖心沉积物的生物硅含量平均值，结果表明湖心沉积物生物硅含量平均值（2.3%）显著高于河流沉积物（0.7%）和岸边表土（0.8%），可初步判断青海湖沉积物生物硅主要由湖内硅藻贡献。结合提取生物硅前后沉积物中硅藻和植硅石含量变化的对比实验，发现未经碱液处理的青海湖湖心沉积物含有大量硅藻，远多于河流沉积物和表土中的硅藻数量。经碱液处理后均未发现完整硅藻，说明碱液提取效率较高，硅藻基本都被溶解。碱液处理前后植硅石的数量变化不大，说明用于提取生物硅的低浓度碱液对植硅石的溶解不明显。因此可以初步认为提取的湖泊沉积物生物硅主要是由湖内硅藻贡献的。 （3） 将青海湖生物硅含量与TOC、粒度等指标作对比分析，发现长尺度上生物硅含量与TOC、粒度等指标变化情况基本一致，反映了长时间尺度气候变化对湖泊/流域生产力的影响。在短尺度上，生物硅与TOC无明显相关性；与粒度相关关系也不稳定且部分时段甚至呈反相变化，可能与气候及不同端元沉积物相互稀释等因素有关。本文的工作表明不同时间尺度上生物硅所指示的气候意义有所不同。因此，今后在应用生物硅作为代用指标时应根据不同时间尺度分别讨论。 |
| 英文摘要 | Knowledge of the climatic changes during the late Holocene, especially during the last two thousand years, is critical in predicting the climatic changes in the future. Increasing lines of evidence have been provided based on variable paleaoclimatic archives during the past several decades, including lake sediments, ice cores, speleothem, peat sediments, and tree rings, etc. Lake sediments are one of the most important paleaoclimatic archive and have been applied widely to reconstruct climatic changes during the past 2,000 years, as they contain high resolution, continuous and sufficient climatic information. Biogenic silica is an important one among the large number of physical, chemical and biological proxy indices extracted from lake sediments. Biogenic Silica (BSi), is a sort of amorphous silica from diatom, radiolarians, sponges, and other siliceous organisms. The BSi content variations may reflect spatial and temporal changes in primary productivity. It has been widely used to study lake, oceanic productivity and paleaoclimatic changes. However, due to different environments various lakes have, such as climatic conditions, watershed vegetation, and the bedrocks, the BSi records environment/climate change differently. The environment/climate significances of BSi are therefore quite different in diverse lake systems. It is necessary to investigate the general laws in BSi% variations for different lakes, and choose some typical lakes to study the climatic significance of BSi proxy in particular. In the present study, we firstly choose ten lakes, which are mainly located in the northeastern, northwestern and southwestern China, to investigate the BSi content changes. By regional comparisons, we discussed the general laws of BSi% changes and the causes for different lakes. Secondly, we studied the environment/climate significance of BSi index in some typical lakes, e.g., Lake Qinghai. Lake Qinghai, the largest inland closed basin in China, is an ideal area for studying global climate changes and related mechanisms, due to its special geographic location in the semi-arid area of Asia and its sensitivity to climate changes. Although numerous works have been carried out to study climatic changes at Lake Qinghai during the last several decades, the environment/climate significance of BSi is still less documented. We therefore applied a multi-proxy-index study to constrain the climatic significance of BSi in Lake Qinghai and to reconstruct climatic changes over there during the last 2000 years. The proxy indices involved here include BSi%, grain size, magnetic susceptibility, and total organic carbon (TOC). The primary results and conclusions are as follows: (1) Comparing the average values of BSi% in different lakes, we find that the average values of BSi% in the northwestern China are lower than that in the northeastern and southwestern China. It maybe attributed to lower temperature and less precipitation in the northwestern China. Such climate condition limits the algae growth and leads to the lower biomass. The average values of BSi% in the northeastern and southwestern China are relatively higher, but the causes are different. The two lakes in northeastern China are largely impacted by human, and they are rich in nutrients. Despite the lower mean annual temperature in northeastern China, there are more nutrients abundantly provided for algae growth. The lakes in the southwestern China studied in this study are generally oligotrophic lakes. The higher BSi contents are most likely due to higher temperature and precipitations. (2) We measured the percentage of BSi for lake sediments, river sediments, and surface soils within the Lake Qinghai catchment. The results show that the average of BSi% in lake sediments (2.3%) is significantly higher than those of the river sediments (0.7%) and the surface soils (0.8%). So it is preliminarily concluded that the BSi of lake sediments are mostly contrib |
| 中文关键词 | 湖泊沉积物 ; 生物硅 ; 青海湖 ; 环境意义 ; 气候变化 |
| 英文关键词 | lake sediments Biogenic silica lake Qinghai environmental significance climate change |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 环境科学 |
| 来源机构 | 中国科学院地球环境研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287368 |
| 推荐引用方式 GB/T 7714 | 刘斌. 我国湖泊沉积物生物硅记录及其环境指示意义——以青海湖为典型案例[D]. 中国科学院大学,2014. |
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