Ferromanganese crusts as archives of deep water Cd isotope compositions
Ferromanganese crusts as archives of deep water Cd isotope compositions
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DOI：
10.1029/2009gc002987
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发表时间：
2010-04-01
影响因子：
3.5
通讯作者：
Hein, J. R.
中科院分区：
文献类型：
--
作者：
Horner, T. J.;Schonbachler, M.;Hein, J. R.
海水中镉的地球化学已引起了极大的关注，由于这种元素的营养属性。最近的培养研究表明，镉是一种重要的生物微量金属，在无机碳的封存中发挥作用。这一结论是支持最近的同位素数据镉溶解在海水中，并纳入养殖浮游植物。这些结果表明，浮游生物的特点是轻镉同位素，而镉贫化表面沃茨通常表现出互补的重镉同位素组成。900米深度以下的海水样品显示出均匀的中等同位素组成，Cd-114/110 = +3.3 +/- 0.5。本研究调查是否铁锰（Fe-Mn）结壳是强大的档案深水镉同位素组成。为此，利用双尖峰多接收器电感耦合等离子体质谱法获得了大西洋、太平洋、印度洋和南大洋15个铁锰结壳和两个美国地质调查局铁锰参考结核最近生长表面的镉同位素数据。铁锰结壳的Cd-114/110平均值为+3.2 +/- 0.4（2 SE，n = 14）。除一个样本外，所有样本的数据与平均深水Cd同位素值相同，分析不确定度为+/- 1.1 <$Cd-114/110（2 SD）。这表明铁锰结壳记录的海水Cd同位素组成没有明显的同位素分馏。来自南大洋的一个单一样品表现出轻镉同位素组成的Cd-114/110 = 0.2 +/- 1.1。这个签名的起源尚不清楚，但它可能反映了在深水镉同位素组成的变化有关的差异，在地表水镉的利用或长期变化的海水Cd-114/110。结果表明，时间序列分析的铁锰结壳可以用来研究海洋镉利用的变化。
The geochemistry of Cd in seawater has attracted significant attention owing to the nutrient-like properties of this element. Recent culturing studies have demonstrated that Cd is a biologically important trace metal that plays a role in the sequestration of inorganic carbon. This conclusion is supported by recent isotope data for Cd dissolved in seawater and incorporated in cultured phytoplankton. These results show that plankton features isotopically light Cd while Cd-depleted surface waters typically exhibit complimentary heavy Cd isotope compositions. Seawater samples from below 900 m depth display a uniform and intermediate isotope composition of epsilon Cd-114/110 = +3.3 +/- 0.5. This study investigates whether ferromanganese (Fe-Mn) crusts are robust archives of deep water Cd isotope compositions. To this end, Cd isotope data were obtained for the recent growth surfaces of 15 Fe-Mn crusts from the Atlantic, Pacific, Indian, and Southern oceans and two USGS Fe-Mn reference nodules using double spike multiple collector inductively coupled plasma mass spectrometry. The Fe-Mn crusts yield a mean epsilon Cd-114/110 of +3.2 +/- 0.4 (2 SE, n = 14). Data for all but one of the samples are identical, within the analytical uncertainty of +/- 1.1 epsilon Cd-114/110 (2 SD), to the mean deep water Cd isotope value. This indicates that Fe-Mn crusts record seawater Cd isotope compositions without significant isotope fractionation. A single sample from the Southern Ocean exhibits a light Cd isotope composition of epsilon Cd-114/110 = 0.2 +/- 1.1. The origin of this signature is unclear, but it may reflect variations in deep water Cd isotope compositions related to differences in surface water Cd utilization or long-term changes in seawater epsilon Cd-114/110. The results suggest that time series analyses of Fe-Mn crusts may be utilized to study changes in marine Cd utilization.