The molybdenum isotopic composition of the modern ocean
The molybdenum isotopic composition of the modern ocean
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DOI：
10.2343/geochemj.1.0158
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发表时间：
2012-04
影响因子：
0.8
通讯作者：
Y. Nakagawa;S. Takano;M. Firdaus;K. Norisuye;T. Hirata;D. Vance;Y. Sohrin
中科院分区：
文献类型：
--
作者：
Y. Nakagawa;S. Takano;M. Firdaus;K. Norisuye;T. Hirata;D. Vance;Y. Sohrin
钼（Mo）同位素组成的自然变化作为地球化学工具的潜力越来越大。虽然海洋是钼的重要储存库，但有关海水中钼同位素组成的数据却很少。我们最近开发了一种基于使用螯合树脂的预浓缩和通过多收集器电感耦合等离子体质谱（MC-ICP-MS）的测量来精确测定Mo同位素比率的新方法，这使得我们能够测量每种稳定的Mo同位素（Nakagawa等人，2008年）。在这项研究中，分析了从太平洋、大西洋和南大洋的9个站点获得的172个海水样本，提供了全球覆盖范围和第一个完整的深度剖面。δ A/95 Mo平均同位素组成（相对于约翰逊Matthey Mo标准品溶液）如下：δ 92/95 Mo =-2.54 ± 0.16‰（2SD），δ 94/95 Mo =-0.73 ± 0.19‰，δ 96/95 Mo = 0.85 ± 0.07‰，δ 97/95 Mo = 1.68 ± 0.08‰，δ 98/95 Mo = 2.48 ± 0.10‰，δ 100/95Mo = 4.07 ± 0.18‰。δ值与A-Mo的原子质量呈良好的线性关系（R2 = 0.999）。钼同位素的三同位素图拟合直线，其斜率与质量相关的同位素分馏的理论值一致。这些结果表明，钼同位素分布均匀，并遵循质量依赖的分馏规律在现代含氧海洋。此外，Mo同位素分析显示，本研究中使用的标准品的δ 98/95 Mo比Archer和万斯（2008）使用的Mo标准品轻0.117 ± 0.009‰。为了准确比较不同实验室的钼同位素组成，迫切需要一个通用的钼标准。另一方面，我们的研究结果有力地支持了海水作为Mo同位素组成国际参考物质的可能性。
Natural variations in the isotopic composition of molybdenum (Mo) are showing increasing potential as a tool in geochemistry. Although the ocean is an important reservoir of Mo, data on the isotopic composition of Mo in seawater are scarce. We have recently developed a new method for the precise determination of Mo isotope ratios on the basis of preconcentration using a chelating resin and measurement by multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), which allows us to measure every stable Mo isotope (Nakagawa et al., 2008). In this study, 172 seawater samples obtained from 9 stations in the Pacific, Atlantic, and Southern Oceans were analyzed, giving global coverage and the first full depth-profiles. The average isotope composition in δ A/95 Mo (relative to a Johnson Matthey Mo standard solution) was as follows: δ 92/95 Mo = ‐2.54 ± 0.16‰ (2SD), δ 94/95 Mo = ‐0.73 ± 0.19‰, δ 96/95 Mo = 0.85 ± 0.07‰, δ 97/95 Mo = 1.68 ± 0.08‰, δ 98/95 Mo = 2.48 ± 0.10‰, and δ 100/95 Mo = 4.07 ± 0.18‰. The δ values showed an excellent linear correlation with atomic mass of A Mo (R 2 = 0.999). Three-isotope plots for the Mo isotopes were fitted with straight lines whose slopes agreed with theoretical values for mass-dependent isotope fractionation. These results demonstrate that Mo isotopes are both uniformly distributed and follow a mass-dependent fractionation law in the modern oxic ocean. In addition, Mo isotopic analysis revealed that δ 98/95 Mo of the standard used in this study was 0.117 ± 0.009‰ lighter than the Mo standard that was used by Archer and Vance (2008). A common Mo standard is urgently required for the precise comparison of Mo isotopic compositions measured in different laboratories. On the other hand, our results strongly support the possibility of seawater as an international reference material for Mo isotopic composition.