Nickel isotopic compositions of ferromanganese crusts and the constancy of deep ocean inputs and continental weathering effects over the Cenozoic
Nickel isotopic compositions of ferromanganese crusts and the constancy of deep ocean inputs and continental weathering effects over the Cenozoic
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DOI：
10.1016/j.epsl.2013.05.019
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发表时间：
2013-08-01
影响因子：
5.3
通讯作者：
Hein, J. R.
中科院分区：
文献类型：
--
作者：
Gall, L.;Williams, H. M.;Hein, J. R.
利用MC-ICPMS分析了来自不同洋盆的24个铁锰结壳表层样品，采用双尖峰质量偏差校正，研究了铁锰结壳镍同位素组成的全球变化。铁锰结壳的δ Ni-60同位素组成比迄今报告的任何其他样品都重得多（-0.1 ‰至0.3 ‰），表面碎屑在0.9 ‰至2.5 ‰之间（相对于NIST SRM 986）。有没有很好地解决海洋盆地之间的差异，虽然数据表明，在大西洋比在太平洋的值轻一些，也没有任何证据表明，这些变化与生物分馏，存在不同的水团，或底层水氧化还原条件。红土样品的初步数据表明，风化伴随着镍的同位素分馏，这将导致河流和海水的同位素重。这与在靠近大陆区域取样的结壳中记录的同位素组成比平均值略重的情况是一致的。此外，生长在热液源附近的结壳的同位素组成集中在千分之1.5左右，这表明进入海洋的热液流体可能具有类似于这一数值的镍同位素组成。根据这些数据，铁锰结壳的重镍同位素组成可能是由于输入的同位素重镍从大陆风化作用，也可能是从热液流体的海洋。通过一个地壳，CD 29 -2，从太平洋中北部的深度剖面显示在过去的76万年镍同位素组成（1.1-2.3千分之一）的变化很大。虽然可能有一些重新分配的镍与磷酸盐化，有没有系统的镍同位素组成之间的差异，更深，更老的部分和更浅，更年轻的部分地壳，这可能表明，海洋来源和汇的镍在很大程度上保持在稳定状态的新生代。此外，同位素配置文件是一致的锰浓度通过同一地壳的配置文件。这意味着铁锰结壳中记录的镍同位素组成与镍通过热液活动释放到海洋之间存在联系。这支持了从地表数据得出的结论，即铁锰结壳中的镍同位素比值在很大程度上受镍海洋输入源的同位素组成控制。(c)2013 Elsevier B. V.保留所有权利。
The global variability in nickel (Ni) isotope compositions in ferromanganese crusts is investigated by analysing surface samples of 24 crusts from various ocean basins by MC-ICPMS, using a double-spike for mass bias correction. Ferromanganese crusts have delta Ni-60 isotopic compositions that are significantly heavier than any other samples thus far reported (-0.1 parts per thousand to 0.3 parts per thousand), with surface scrapings ranging between 0.9 parts per thousand and 2.5 parts per thousand (relative to NIST SRM986). There is no well resolved difference between ocean basins, although the data indicate somewhat lighter values in the Atlantic than in the Pacific, nor is there any evidence that the variations are related to biological fractionation, presence of different water masses, or bottom water redox conditions. Preliminary data for laterite samples demonstrate that weathering is accompanied by isotopic fractionation of Ni, which should lead to rivers and seawater being isotopically heavy. This is consistent with the slightly heavier than average isotopic compositions recorded in crusts that are sampled close to continental regions. Furthermore, the isotopic compositions of crusts growing close to a hydrothermal source are clustered around similar to 1.5 parts per thousand, suggesting that hydrothermal fluids entering the ocean may have a Ni isotopic composition similar to this value. Based on these data, the heavy Ni isotopic compositions of ferromanganese crusts are likely due to input of isotopically heavy Ni to the ocean from continental weathering and possibly also from hydrothermal fluids. A depth profile through one crust, CD29-2, from the north central Pacific Ocean displays large variations in Ni isotope composition (1.1-2.3 parts per thousand) through the last 76 Myr. Although there may have been some redistribution of Ni associated with phosphatisation, there is no systematic difference in Ni isotopic composition between deeper, older parts and shallower, younger parts of the crust, which may suggest that oceanic sources and sinks of Ni have largely remained in steady state over the Cenozoic. Additionally, the isotope profile is in agreement with a profile of Mn concentration through the same crust. This implies a link between the Ni isotopic composition recorded in ferromanganese crusts and the release of Ni into the ocean through hydrothermal activity. This supports the conclusions drawn from surface data, that Ni isotope ratios in ferromanganese crusts are largely controlled by the isotopic compositions of the Ni oceanic input sources. (c) 2013 Elsevier B.V. All rights reserved.