| 摘要: |
| 对海洋初级生产力贡献约 40%的硅藻, 在全球气候与碳循环中扮演着重要的角色。硅藻稳定同位素(δ30Si 和 δ18O, δ13C 和 δ15N)测试对象分别为从海洋沉积物中提取的纯硅藻壳体的生物硅和氧及其内嵌有机质的碳和氮。联合运用各种物理分离(去有机质、碳酸盐, 筛分, 差异沉降, 重液浮选以及微池分流重力场流分离技术)和化学纯化技术从沉积物中提纯出硅藻是其稳定同位素古海洋学应用的前提。确定硅藻δ15N 两种制样过程(燃烧和湿式消解)中是否分别存在大气 N2 和非 NO3?组分的污染; δ30Si 分析中氟化剂使用的避免、 制样方法的改进以及 MC-ICP-MS 对硅同位素分辨能力的提高; δ18O分析中硅藻壳体外层不稳定氧的完全有效去除, 是其同位素古海洋学应用范围扩大和精度提高的关键。硅藻δ13C 能评估大气 PCO2 和海洋初级生产力变化; δ15N和 δ30Si 可定量示踪海洋硝酸盐和硅酸等营养物利用程度; δ18O则记录了海表温度和海水氧同位素组成。硅藻稳定同位素信号单一, 受后期改造作用弱, 生命效应低, 解译针对性强, 在两极和赤道少(或缺)有孔虫海区应用广泛。在此基础上, 对目前该领域中存在的问题及未来的研究方向进行了阐述。
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| 关键词: 硅藻, 稳定同位素, 海洋沉积物, 碳循环 |
| DOI：10.11693/hyhz201004027027 |
| 分类号: |
| 基金项目:国家重点基础研究发展计划项目“大洋碳循环与气候演变的热带驱动”, 2007CB815903 号; 国家自然科学基金项目“低纬度西太平洋硅藻席沉积与碳循环”, 40776031 号资助。 |
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| A REVIEW OF DIATOM STABLE ISOTOPES IN PALAEOCEANOGRAPHY |
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LI Tie-Gang1,2, XIONG Zhi-Fang1
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1.Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences;2.Graduate University of Chinese Academy of Sciences
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| Abstract: |
| Diatom accounts for about 40% of marine primary productivity, and therefore plays an important role in the global climate and carbon cycle systems. Diatom stable isotopic measurements (δ30Si, δ18O, δ13C and δ15N) are based on the silicon and oxygen in the silica tetrahedron, and carbon and nitrogen in the intrinsic organic matter of purified diatom frustules extracted from marine sediments. The palaeoceanographic implications of diatom stable isotopes rely on the pure diatom isolated from sediments by combining several physical separation methods (i.e. bulk organic and carbonate material removal, sieving, differential settling, heavy liquid flotation, and split-flow lateral-transport thin separation) and chemical purification procedures. Confirming whether the atmospheric N2 or non-NO3? compounds contaminate diatom δ15N in the traditional combustion and new wet digestion method, avoiding the use of fluorinating gases, improving sample preparation techniques, increasing the resolution capacity of MC-ICP-MS for silicon isotopes in the δ30Si analyses, and removing the labile oxygen of outer and hydrous layer in diatom silica completely and effectively are key to the scope and precision of palaeoceanographic implications of its stable isotopes. Diatom δ13C is used to evaluate the partial pressure of atmospheric CO2 (PCO2) and oceanic primary productivity; δ15N and δ30Si are adopted to indicate the relative utilization degree of marine nitrate and silicic acid quantitatively; and δ18O is believed to record the sea surface temperature and oxygen isotopic composition of seawater. Diatom stable isotopes, with the advantage of single signal, weak post-alteration, low vital effects and more relevant interpretation, are widely applied to the polar and equatorial ocean where foraminifera and calcareous nannofossils are scarce or absent. In this review, we point out the present problems and give some prospects in the field of marine diatom stable isotopic study.
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| Key words: Diatom, Stable isotope, Marine sediment, Carbon cycle |
