Knowledge Resource Center for Ecological Environment in Arid Area
| 格陵兰NEEM冰芯粉尘来源与生物活性元素Fe研究 | |
| 其他题名 | The study of dust sources and bioavailable iron in Greenland NEEM ice core |
| 杜志恒 | |
| 出版年 | 2016 |
| 学位类型 | 博士 |
| 导师 | 效存德 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 冰芯被认为是最主要的古气候代用资料，为第四纪气候研究提供了黄土与海洋沉积物所无法获得的古环境信息。格陵兰冰盖作为当前全球最主要的两大冰盖之一，从该地区获取的冰芯具有高积累率、高分辨及长时间尺度等优点。因此，从该地区获取的冰芯，可以很好的重建过去古气候信息。2010年，由丹麦哥本哈根大学所倡导，并联合了14个国家在格陵兰西北部NEEM营地 (The North Greenland Eemian Ice Drilling；77.45°N 51.06°W，msl，2479m) 历时3年钻取了一支长2540m的透底冰芯，该冰芯是继格陵兰NGRIP (2003年) 冰芯后在该地区获取的另一支深冰芯，其主要用于解决Eemian时期气候之谜。冰冻圈科学国家重点实验室作为NEEM冰芯的中方参与单位，参加了NEEM营地冰芯的钻取工作，并获得以下样品。1、根据NEEM科学委员会协议，以5m为分辨率截取20cm为一个样品，共计分得330个冰芯样品，这些冰芯样品涵盖了过去11万年的古气候信息；2、获取了一个深4m的雪坑样品；3、与韩国共享一支80m浅冰芯以供相关研究。本论文通过直接用HNO3酸化与HF+HNO3消解两种方法，测试了NEEM雪坑痕量元素的浓度(包括可溶与总浓度)。结果表明：痕量元素在格陵兰雪坑中表现出很好的年际特征，特别在春季存在显著的峰值。此外，通过对NEEM雪坑可溶与总元素富集系数对比得出：对于一些具有指示环境意义的元素 (如Pb、Ba、Cu等元素) 而言，传统直接酸化法计算得出的元素富集系数可能高估了元素的真实值。同时发现，2006年作为中国西部沙尘暴频发年，NEEM雪坑中痕量元素浓度在此年表现出峰值。本论文通过再分析资料与后向轨迹法，进一步证实了这一结论。并初步提出了中亚沙漠粉尘向格陵兰地区传输机制。对NEEM冰芯样品稀土元素 (REE) 的研究表明：不同时期稀土元素浓度差异显著，主要表现为冷期浓度高，暖期浓度低的特征。在全新世时期，尽管其浓度较低，但其可溶REE/总可溶REE变化幅度较大，这与暖期矿物粉尘来源相对复杂有关。稀土元素浓度与δ18O之间显著负相关表明：其主要受当时气候环境的影响，即温度的调控作用。由于稀土元素性质稳定，不易受环境状态及风化等因素的影响，使得NEEM冰芯稀土元素标准化分布与地壳源信息非常类似；结合潜在源区稀土元素的特征及Sr-Nd同位素结果，从长时间尺度，证实了中亚沙漠粉尘对格陵兰地区粉尘的贡献大小不同。对于冰期时期而言，塔克拉玛干沙漠是其主要来源；对于温暖的全新世而言，中国北方沙漠是其主要来源，但该结论仍需通过大气环流与气候模型进一步验证。最后，通过对NEEM冰芯中可溶与总可溶Fe元素的测试，结合中国石笋δ18O同位素信息与中国西部黄土剖面数据，揭示出太阳辐射是控制北半球气候的主要因素，也是衔接中、高纬度气候一致变化的主要因素之一；对于千年时间尺度快速气候事件，NEEM冰芯粉尘微粒数与中国西部古浪黄土粉尘粒径之间存在非常一致的对应关系，这种同步变化表明：北极冷气团南下，将中亚沙漠粉尘通过西风急流向北移动传输到格陵兰地区。NEEM冰芯生物活性元素Fe数据表明：在北半球，粉尘-Fe施肥效应在不同时期的调节作用不同，可溶性Fe/总可溶性Fe (DFe/TDFe) 在全新世与末次间冰期其值高于末次冰期冰盛期 (LGM)；此外，NEEM冰芯生物活性元素Fe数据表明，其浓度比南极冰芯生物活性元素浓度高2-3个数量级。尽管南大洋是全球最大的“高叶绿素、低粉尘区”，但是北半球粉尘蕴含了更多的生物活性元素Fe。因此，“Fe施肥效应”研究在北半球应得到重视。 |
| 英文摘要 | Polar ice core have provided the important knowledge of the climate variations over hundreds of thousands of years. Because it can capture the wind-blown continental and marine material aerosols. Therefore, it is taken as an excellent archive of past environmental conditions and paleo-atmospheric compositions. The Eemian, or the last interglacial period, is the last time climate was as warm as it is today. The North Greenland Eemian Ice Drilling (NEEM) is an international ice core research project aimed at retrieving an ice core from North-West Greenland (camp position 77.45°N 51.06°W, surface elevation 2450m, mean annual temperature -29°C, accumulation of 0.22m ice equivalent/yr) reaching back through the previous interglacial, the Eemian. The project logistics is managed by the Centre for Ice and Climate, Denmark, and 13 other countries are taking part in the word. The 2540 m long NEEM ice core was drilled during field seasons 2008 to 2012. The drill site is located downstream on the ice ridge that runs N-NW from the summit of the Greenland ice sheet where the GRIP core was extracted. The State Key Laboratory of Cryospheric Science in China is one of participating members, shared about 330 sections of NEEM ice core, the size of each one is 3.5cm*3.5cm*20cm, according to the Scientific Committee conference. Besides, a 4m snowpit is digged to measure the trace elements at NEEM camp, and we shared an shallow ice core about 87m with Korea Polar Research Institute. For NEEM snowpit, we focus on the soluble and total trace elements, such as Fe, Al, Ca, Ti, Cu, Ba and Zn, which used the acid leach method and digest method (HF+HNO3). We investigate trace element records in snowpit samples obtained from the northwestern Greenland ice sheet near the North Greenland Eemian Ice Drilling (NEEM) camp in 2009. Our result show the concentrations of trace elements in acid leachable method have higher Enrichment Factor than that of values in total concentration with HF+HNO3 digest method, indicating the EFs in acid leachable method are overestimated in previous studies. In particular, the soluble Fe seem to be crust source, and concentrations of trace elements (including souble and total) in NEEM snopit shows seasonal deposition events with maxima in the winter–spring layers. Moreover, an anomalous atmospheric mineral dust event was recorded corresponding to late winter 2005 to spring 2006. A back trajectory analysis suggests that a major contributor to the Greenland aerosol was an air mass passing over the Canadian Arctic and North America. Several trajectories point to Asian regions as a dust source. The mineral dust deposited at NEEM was strongly influenced by long-range atmospheric transport and dust input from arid source areas in northern China and Mongolia. In this study, I present the soluble and total soluble Rare Earth Elements (REE) concentration record determined in 155 sections of an NEEM ice core, covering a period over the past 110 kyr BP. REE allow a detailed quantitative evaluation of aeolian dust composition because of the large number of variables (14 elements). REE concentrations match the particulate dust concentration profile over this period and show a homogeneous crustal-like composition during the Last Glacial Maximum (LGM). The normalization patterns of REE are significantly difference in different periods, which may highlight the alternation of multi-dust sources contributions from different sources. In particular, the normalization patterns of REE and Sr-Nd isotopes from Greenland ice cores and potential source areas, which further demonstrate the Taklamakan desert is the most important dust source for Greenland region. We observe that the frequent changes in REE composition at the D-O cycles are linked in turn to wind strength and/or the path of the atmospheric trajectory. Although the dust concentrations remained fairly low, a notable return towards more glacial dust characteristics is recorded during the cold periods.Mineral dust can directly affect climates by supplying iron and other essential bioavailable elements to the ocean. I slso present the dissolved iron (DFe) and total dissolved iron (TDFe) concentrations that have accumulated in the NEEM ice core over the past 110 kyr BP. In the NEEM ice core, the bioavailable Fe concentrations were positively correlated with the dust and Ca2+ concentrations and significantly and negatively correlated with the δ18O and CO2 concentrations. The DFe/TDFe ratios were higher during warm periods (Holocene and the last interglacial period) than during cold periods (the last glacial maximum), which indicated that the biological pump effect is disturbed more during warm periods than during cold periods. In addition, our study shows that the changes in the iron flux between the NEEM ice core and Asian loess records are consistent with the summer insolation in the northern Hemisphere. These results emphasize that the variability of bioavailable reactive elements is most likely driven by solar radiation and dust in the northern hemisphere. |
| 中文关键词 | 格陵兰冰盖 ; NEEM冰芯 ; 中国黄土 ; 中亚沙漠 ; 痕量元素 |
| 英文关键词 | “Greenland ice sheet”“NEEM ice core”“Chinese loess”“Asian Desert”“Trace elements” |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 自然地理学 |
| 来源机构 | 中国科学院西北生态环境资源研究院 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287705 |
| 推荐引用方式 GB/T 7714 | 杜志恒. 格陵兰NEEM冰芯粉尘来源与生物活性元素Fe研究[D]. 中国科学院大学,2016. |
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