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| 青藏高原东南边缘横断山区降水稳定同位素变化及与水汽来源关系研究 | |
| 其他题名 | Relationships between Stable Isotopes in Precipitation and Different Moisture Sources over the Hengduan Mountains at the Southeastern Margin of Tibetan Plateau |
| 韦飞黎 | |
| 出版年 | 2017 |
| 学位类型 | 硕士 |
| 导师 | 余武生 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 摘 要降水稳定同位素与大气环流及其过程之间存在着密切的联系，其变化受温度、湿度、水汽来源等不同要素的影响。近年来，中国降水稳定同位素研究取得很大的进展，尤其在中国东部季风区、西北干旱半干旱区和青藏高寒区等不同区域降水稳定同位素的空间差异研究逐步得以深入。然而在青藏高原和云贵高原的过渡地带横断山区，降水稳定同位素研究较为薄弱。横断山区是中国西南水汽的重要通道，也是中国海洋型冰川主要分布区之一，其不同季节的水汽来源及降水水汽的季节转换尚不清楚。因此，在横断山区开展降水稳定同位素研究有利于深刻理解该区域的水汽来源和水循环过程，甚至为该区域冰芯、树轮等古气候记录的重新解译提供重要的指示意义。为此，本研究在横断山区利用稳定同位素示踪技术、后向轨迹追踪模型以及空间对比分析等多手段相结合，开展降水稳定同位素研究，以揭示不同季节的水汽来源与水汽输送方式及其对降水的影响。本研究的主要结论如下：(1) 横断山区南部德钦站点的降水稳定同位素在不同的季节与温度之间的相关不同，具体表现为：在季风爆发前呈正相关，在季风期相关性不显著，季风撤退后呈反相关。但是降水稳定同位素与降水量的关系，在不同时期均呈反相关。通过与横断山区德钦南部的西双版纳相比较发现，德钦降水稳定同位素的季节变化与西双版纳站点类似，在夏季降水稳定同位素的显著贫化均与季风活动有关。西双版纳降水d18O低值持续时间比德钦的长，而且与西双版纳地表抬升指数相比，夏季德钦地表抬升指数为负值持续时间较短，正值持续时间更长，这些结果说明德钦的对流活动持续时间较短，同时伴随季风活动持续时间较短。此外，降水稳定同位素准确捕捉到季风进退的信号。(2) 与南部的德钦站点相似，在横断山区北部的昌都站点，降水稳定同位素仅在西风活动期与温度呈正相关。在整个观测期间，降水稳定同位素与降水量呈负相关，尤其是在季风期，二者之间更为显著。昌都降水稳定同位素的季节变化能够有效地指示不同季节水汽来源的变化，特别是能够捕捉到印缅槽（即西风南支槽）活动以及印度季风活动的信号。在西风活动期 (1?3月和11?12月)，降水稳定同位素变化趋势与温度变化趋势一致；在印缅槽活动期 (4?5月和10月)，降水稳定同位素出现突然降低特征。与季风前期和季风后期降水稳定同位素偶尔出现突然降低不同，在季风活动期 (6?9月)，昌都降水稳定同位素持续呈现持续低值特征。(3) 雨滴在降落过程中受局地水汽再循环的影响，导致横断山区大气水线偏离全球大气水线。从更大的范围来看，大气水线的斜率从更南部的西双版纳到德钦再到昌都越来越低，说明从南到北降水稳定同位素受非平衡分馏作用逐渐增强，指示了受局地蒸发活动及局地水汽再循环影响越来越强烈。本研究拓宽了青藏高原降水稳定同位素的研究范围，弥补了横断山区降水稳定同位素资料的不足，特别是研究发现，非季风期降水对降水稳定同位素产生很大的影响。而季风爆发前由印缅槽引起的降水对植物生长具有重要的影响，且季风爆发前和季风撤退后由于空气温度相对更低，由印缅槽活动引起的降水会更有利冰或雪等物质的保存。因此，在利用树轮或冰芯等重建古气候变化时，需要考虑到非季风期降水的影响。这一研究在古气候记录的重新解译方面具有一定的创新性。 |
| 英文摘要 | ABSTRACTStable isotopes in precipitation are related to atmospheric circulation patterns and transport paths, and also affected by changes in temperature, humidity, moisture sources and other factors. In the last few decades, the isotopic composition of precipitation inChinaprecipitation has been widely surveyed, especially in eastern monsoon region, arid and semi-arid regions of northwesternChina, and the Tibetan Plateau. In comparison, a gap remains in understanding stable isotopes in precipitation on the Hengduan Mountains, which acted as a transitional zone between the Tibetan Plateau and the Yungui Plateau. Warm summer moisture from the Indian Ocean is transported into the southwest ofChinavia the Hengduan Mountains, an important trajectory that results in abundant precipitation, and the region of the Hengduan Mountains thus provides an important link between the Yungui Plateau and the Tibetan Plateau. It is necessary to determine the different moisture sources and moisture transport processes in the Hengduan Mountains in different seasons to better understand the changes in the water cycle over the larger region from the Yungui Plateau to the Hengduan Mountains and then to the Tibetan Plateau. Additionally, such studies will be helpful to reinterpret the δ18O and δD records in ice cores and tree-rings derived from the Hengduan Mountains.Therefore, this study focuses on relationships between precipitation stable isotopes and different moisture sources on the Hengduan Mountains at the southeastern margin of Tibetan Plateau. The results of our data show that:(1) At the Deqin station (located at the southern Hengduan Mountains), correlations between stable isotopes (δ18O and δD) in precipitation and temperature varied in different seasons during the whole sampling period: before the Asian summer monsoon onset, a significant positive correlation existed; during the Asian summer monsoon, no correlation existed; and during the post-monsoon season, a significant inverse correlation existed. In comparison, there is an apparent inverse correlation between stable isotopes and precipitation amount existed before the Asian summer monsoon onset, during the Asian summer monsoon, and after monsoon season retreat. In addition, the overall temporal variations of δ18O and δD in precipitation from Deqin are similar to those from a southern station at Xishuangbanna. Both stations demonstrate considerably depleted precipitation δ18O values in the summer as a consequence of intense Asian summer monsoon activities. However, at Xishuangbanna, the occurrences of the timing and duration of the depleted δ18O values, as well as the negative surface lift index values, occur earlier and last longer than those at Deqin. These results indicate that the Asian summer monsoon onset is later and that the duration of the monsoon activities is shorter at Deqin relative to Xishuangbanna. This means that the stable isotopes in precipitation accurately captures the signal of the time when the monsoon onset and retreat.(2) At Qamdo (located at the northern Hengduan Mountains), the δ18O and δD values of precipitation at Qamdo during the entire sampling period were inversely correlated with precipitation amount and demonstrated an apparent “amount effect.” In comparison, the relationship between precipitation stable isotopes and temperature was very weak, and the “temperature effect” only existed in the dry season. The fluctuations of precipitation stable isotopes at Qamdo during the different seasons revealed various moisture sources. The westerlies and local recycling moisture dominated at the study area before the pre-monsoon and after the post-monsoon seasons, which resulted in similar trends of both precipitation stable isotopes and temperature. The marine moisture combined was transported to the northern Hengduan Mountains by the winter India-Burma Trough (the southern branch trough of the westerlies) with convection. Consequently, stable isotopes in subsequent precipitation were occasionally observed to decrease suddenly. However, δ18O and δD values of precipitation at Qamdo were lower during the monsoon period and the duration of those low values was longer because of the effects of the Indian Summer Monsoon and the strengthening convection. Our findings demonstrated that stable isotope records in precipitation from the northern Hengduan Mountains captured signals of the winter India-Burma Trough and the Indian Summer Monsoon. (3) In the process of precipitation, the raindrops are affected by the local sub-cloud re-evaporation and local recycling moisture, which resulted in the Local Meteoric Water Line (LMWL) at Qamdo deviating from the Global Meteoric Water Line (GMWL). Overall the slopes of LMWLs were lower with gradually strengthening non-equilibrium fractionation from south to north (from Xishuangbanna to Deqin, and to Qamdo). The resulte indicated that the influences of re-evaporation and local recycling moisture were intense gradually from south to north.Our findings indicate that precipitation in the northern Hengduan Mountain caused by the India-Burma Trough before the monsoon season is of great significance for the growth of plants. Moreover, precipitation induced by the winter India-Burma Trough activities during the pre-monsoon and post-monsoon season should be more conducive to the preservation of mass (ice/snow) because of the relatively lower temperature. Therefore, the non-monsoon precipitation also has a more important effect on stable isotope records of tree-rings or ice cores from the Hengduan Mountains compared with the monsoon precipitation. It is necessary to consider the effects of different seasonal precipitation regimes caused by various climate systems, including the winter India-Burma Trough and the Indian Summer Monsoon, while interpreting the paleoclimatic information preserved in tree-rings and ice cores from the Hengduan Mountainous, especially the non-monsoon precipitation |
| 中文关键词 | 降水 ; 稳定同位素 ; 水汽来源 ; 横断山区 |
| 英文关键词 | precipitation stable isotopes moisture sources Hengduan Mountains |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 自然地理学 |
| 来源机构 | 中国科学院青藏高原研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287900 |
| 推荐引用方式 GB/T 7714 | 韦飞黎. 青藏高原东南边缘横断山区降水稳定同位素变化及与水汽来源关系研究[D]. 中国科学院大学,2017. |
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