天山乌鲁木齐河源 1 号冰川成冰过程的地球化学研究——以低分子有机酸为主

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	天山乌鲁木齐河源 1 号冰川成冰过程的地球化学研究——以低分子有机酸为主
其他题名	The Geochemistry of Ice Forming Processes in Glacier No. 1 at the Ürümqi River Head, Tianshan Mountains: A case study of low mo-lecular weight Organic Acids
	丁文慈
学位类型	硕士
导师	李心清
	2019
学位授予单位	中国科学院大学
学位授予地点	中国科学院地球化学研究所
关键词	有机酸甲酸乙酸草酸沉积后过程 1 号冰川大气污染雪冰化学
摘要	冰川上的表面雪层是联系大气成分与冰芯记录的重要纽带，对雪－冰现代过程的研究将有助于正确解释保存在冰芯中的古气候和环境信息。山地冰川雪冰中有机酸记录的研究在认识有机酸生物地球化学循环方面占很大的优势，本文依托天山冰川观测试验站开展的冰雪物理、化学现代过程方面的研究，对乌鲁木齐河源1号冰川中低分子有机酸和无机阴离子在成冰作用过程中的迁移转化进行了研究。新雪和保存较好的表层雪主要用来分析采样点低分子有机酸和无机阴离子的季节变化特征，粒雪坑样品主要用于进行低分子有机酸和无机阴离子沉积后过程的研究。雪冰样品采集于1号冰川东支东经 86°49′，北纬 43°06′，海拔 4 130 m 处，2004 年 3 月至 2005 年 3 月期间，共获取了 23 个连续雪坑剖面的粒雪样品。采用美国 Dionex 公司的 ICS-90 型离子色谱仪加 RFC-30 型淋洗液在线发生器进行测定，检测到的低分子有机酸主要有 HCOO-、CH3COO-、C2H5COO- 和(COO)2 2-，无机阴离子主要有 F-、Cl-、NO2-、NO3-、SO4 2- 和 PO4 3-。表层雪是研究粒雪化和成冰作用过程中化学组成变化的起点。为配合天山乌鲁木齐河源 1 号冰川沉积后过程中化学组成变化的研究，我们首先对表层雪样品（雪坑表层 5cm 的雪样）进行了低分子有机酸和无机阴离子含量的分析。结果显示，除(COO)2 2- 外，大部分有机酸和高浓度的无机阴离子因受到周围环境和盛行风的影响呈现出明显的季节变化特征，即夏半年离子浓度变化剧烈，最大值和最小值同时出现在夏半年，冬半年的浓度则相对小而稳定；而(COO)2 2- 和低浓度的无机阴离子随季节变化的特征不明显，在全年均显示出波动性。数据表明，在外界条件不变的情况下，表层雪可以长时间（至少半年时间）保存其中高含量的化学组成不被改变。通过对高含量低分子有机酸和高含量无机阴离子的沉积后过程的研究，发现它们在沉积后的迁移转化过程受温度和融水的影响较大，在不同时期表现出不同的季节变化特征。雪层消融初期，淋溶作用导致雪层内的大部分离子组分进入初始融水中，并随着融水下渗、聚集，使下部雪层中离子组分的浓度不断增加；当消融进一步加剧，大部分低分子有机酸和无机阴离子随融水径流而流失，雪层中记录的低分子有机酸和无机阴离子含量迅速降低；在消融季节，峰值向雪坑底部移动的速度较快。在冬半年的负温条件下，雪层中记录的低分子有机酸和无机阴离子的含量及其保存在雪坑下部的峰值都相对稳定，这也再次说明如果外界条件不发生改变，雪冰可以长时间（至少半年时间）保存其中的化学组成不被改变这个结论；另外，冬半年雪坑上部记录的峰值在一定程度上可以反映它们在大气中的初始水平。CH3COO- 和(COO)2 2- 的峰值通常会出现在污化层的附近，与污化层的位置具有较好的一致性，说明污化层对CH3COO-和(COO)2 2- 的沉积后过程可能有一定的影响。
其他摘要	Snow-firn pack links the atmosphere and the ice core in geochemical compositions. In order to interpret the records in ice core, the present environmental processes of snow and firn, such as the atmospheric transfer function and the effect of post-depositional processes, need to be known. To investigate the effects of depositional and post-depositional processes on chemical signals recorded in glacier snow and ice, organic acids and inorganic anions were analyzed over the course of one year. The investigation was undertaken as part of the Program for Glacier Processes Investigations (PGPI), which was initiated in July 2002 by the Tianshan Glaciological Station (TGS)。 Snow samples collected during March 2004 to March 2005 field campaign from the accumulation zone of the Glacier No.1 (43°06′N; 86°49′E; 4 130m a.s.l.) at the Ürümqi river head, eastern Tianshan, China, were analyzed for low molecular weight organic acids and inorganic anions by DIONEX ICS-90 Ion Chromatography with RFC-30 Reagent-Free Controller. The organic acids in the sample include HCOO- , CH3COO- , C2H5COO- and (COO)2 2-, while the inorganic anions are F- , Cl- , NO2- , NO3- , SO4 2- and PO4 3-. Surface snow sets the benchmark for identifying post-depositional changes of the geochemical constituent in the ice forming processes. For monitoring the variations of chemical composition in the transforms from snow to ice, low molecular weight organic acids and inorganic anions in surface snow (the topmost 5cm snow in the snow pit) were analyzed. Most of the organic acids except for (COO)2 2- and high-concentration inorganic anions as Cl- , NO3- and SO4 2- demonstrate seasonal variations from April to September, which we believe are primarily caused by strong local atmospheric circulations and the prevailing west wind in the seasons, while much even concentrations in the winter. All the anions changed considerably from the late spring to early autumn, and revealed both the lowest and highest concentrations in a year. On the other hand, (COO)2 2- and low-concentration inorganic anions as F- , NO2 - and PO4 3- showed high variations in the whole year. Our results indicate that the majority of high concentration anions can be preserved in the surface snow for a long time (at least half a year) without changes in their concentra-tions if the weather conditions remain relatively stable. During the post-depositional processes, organic acids and inorganic anions in high-concentrations were analyzed. It is found that the temperature and the percolation of meltwater had a definitive impact on the transformation process. These compositions in snowpits during different periods show visible seasonal characteristics and elution processes. When meltwater appeared in snow pit, they assembled the ions and increased the concentrations of the compositions as they moved downward. And at the same time, successive peaks occur at the upper parts of snow-firn pack. As the temperature reaches above zero completely, meltwater percolated through the snow pit, and leached the ions, however, alteration deeper in the snow-firn pack was slight and the general information was still preserved. When the temperature stayed below zero, the peaks present a stable fluctuation, which can indicate the conclusion again, that the majority of high concentration anions can be preserved in the surface snow for a long time (at least half a year) without changes in their concentrations if the weather conditions remain relatively stable; and to some extent, the peaks in the upper parts of snow-firn packs can represent their primary levels in the atmosphere. We also found that during melting season, the peaks move downward rapidly, while during other seasons the peaks move downward slowly until merging into ice. Furthermore, both CH3COO- and (COO)2 2- peaks coincide with dust layers, this implies that dust layers may have an influence on the elution process of CH3COO- and (COO)2 2-.
页数	71
语种	中文
文献类型	学位论文
条目标识符	http://ir.gyig.ac.cn/handle/42920512-1/10789
专题	研究生
推荐引用方式 GB/T 7714	丁文慈. 天山乌鲁木齐河源 1 号冰川成冰过程的地球化学研究——以低分子有机酸为主[D]. 中国科学院地球化学研究所. 中国科学院大学,2019.

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