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| 达里湖流域地球化学过程与最近6000年东亚夏季风边缘区水文和生态演变 | |
| 其他题名 | Geochemical processes in the Dali Lake catchment: Implications for hydrological and ecological variations in the East Asian summer monsoon margin during the last 6000 yrs |
| 范佳伟 | |
| 出版年 | 2017 |
| 学位类型 | 博士 |
| 导师 | 肖举乐 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 北半球高纬驱动、热带海洋驱动和太阳活动驱动均被认为是百年尺度全球气候变化的主控因素，然而它们对于东亚夏季风变率的相对重要性仍不确定，导致未来全球增温背景下东亚夏季风的演变模式存在激烈争议。本文详细分析了内蒙古中东部达里湖DL04岩芯上部6.39 m沉积物中<38 μm碳酸盐的Ca和Mg含量、Mg/Ca比值、δ18O和δ13Ccarb值以及TOC和TN含量、有机质C/N比值、δ13Corg和δ15N值，基于AMS 14C年代标尺，恢复了最近6000年湖区的水文、生态和气候变化过程。结果表明：达里湖<38 μm碳酸盐主要为湖泊水体沉淀的内源方解石，其Ca和Mg含量、Mg/Ca比值以及δ18O和δ13Ccarb值增大反映湖水蒸发量超过补给水量，进而指示湖区干旱事件。TOC和TN含量减少反映地表径流减弱、湖面降低，湖泊生产率下降、流域植被退化。C/N比值变化反映陆生和水生有机质的相对比例变化而非其绝对量变化。δ13Corg和δ15N值共同增大反映湖区气候变干导致的陆生有机质输入减少、湖面下降导致的湖水碱度升高、溶解氧浓度增加，此外δ13Corg还受到沉积有机质分解作用的显著影响。达里湖沉积内源碳酸盐和有机质地球化学数据表明距今5800-5300、4250-4000、3200-2800、1650-1150和650-300年前，流域地表径流显著减弱、湖面显著降低，湖泊生产率显著下降、流域植被显著退化，湖区气候显著变干。这些数据暗示东亚夏季风强度在上述时段显著减弱。最近6000年东亚夏季风显著减弱事件在定年误差范围内与北大西洋冰漂碎屑事件一致，而与热带西太平洋海表温度变化和太阳活动变化相关性较差，表明百年尺度东亚夏季风强度变化主要受控于北半球高纬气候过程。这些数据暗示全球持续升温可能有利于百年尺度东亚夏季风环流的增强，进而使我国北方半干旱区降水增多。 |
| 英文摘要 | Teleconnections to the northern high latitudes, forcing by the tropical oceans and solar variability have all been suggested as dominant factors in the centennial global climate changes, yet there is little consensus as to the relative importance of these factors for the East Asian summer monsoon (EASM) variability, which results in a highly contested issue about the pattern of EASM variability response to the global warming. In this study, the upper 6.39 m of a sediment core (DL04) recovered in the central part of Dali Lake in central-eastern Inner Mongolia is analyzed for Ca and Mg concentrations, Mg/Ca ratio and δ18O and δ13Ccarb values of <38-μm carbonates; and total organic carbon (TOC) and total nitrogen (TN) concentrations, TOC/TN (C/N) ratio and δ13Corg and δ15N values of organic matter. AMS 14C time series of these proxy data document a detailed process of changes in the hydrology, ecology and climate in the region during the last 6000 yrs. The results indicate that the <38-μm carbonates in the Dali Lake sediments are predominated by endogenic calcites precipitated within the water body of the lake. Increases in the Ca and Mg concentrations, Mg/Ca ratio and δ18O and δ13Ccarb values are interpreted as the intensive evaporative losses overwhelming the water input to the lake and thus the drought events in the region. Meanwhile, decreases in the TOC and TN concentrations indicate weakening in the surface runoffs, decreases in the lake level and phytoplankton productivity, and declines in the terrestrial vegetation. C/N ratios are used to reflect the changes in the relative proportions rather than the absolute amount of terrestrial and aquatic organic matter. In addition, concurrent increases in the δ13Corg and δ15N values indicate decreases in the terrestrial organic matter inputs and increases in the water alkalinity and dissolved oxygen concentration due to decreases in the lake level induced by dry climate in the region, although changes in the δ13Corg values may be also influenced by the degradation of sedimentary organic matter. The geochemical data of endogenic carbonates and organic matter from the Dali Lake sediments suggest that significant weakening in the surface runoffs, decreases in the lake level and phytoplankton productivity, declines in the terrestrial vegetation and drying in the regional climate occurred at the intervals of 5800-5300, 4250-4000, 3200-2800, 1650-1150 and 650-300 cal yr BP. These data indicate that the EASM intensity significantly declined at the above intervals. Large declines in the EASM intensity during the last 6000 yrs correspond, within age uncertainties, to the occurrences of ice rafted debris in the North Atlantic, but not coincide well with the changes in the sea surface temperature of the western tropical Pacific and in the solar activity, indicating that centennial changes in the EASM intensity are mainly controlled by climatic processes occurring in the northern high latitudes. These data imply that persistent global warming may be favorable for the strengthening of the EASM circulation and for the transportation of more rainfall to the semi-arid regions of northern China on centennial scales. |
| 中文关键词 | 达里湖 ; 地球化学 ; 水文生态 ; 东亚夏季风 ; 最近6000年 |
| 英文关键词 | Dali Lake geochemistry hydro-ecology East Asian summer monsoon last 6000 yrs |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 第四纪地质学 |
| 来源机构 | 中国科学院地质与地球物理研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287831 |
| 推荐引用方式 GB/T 7714 | 范佳伟. 达里湖流域地球化学过程与最近6000年东亚夏季风边缘区水文和生态演变[D]. 中国科学院大学,2017. |
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