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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >The magnesium isotope budget of the modem ocean: Constraints from riverine magnesium isotope ratios
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The magnesium isotope budget of the modem ocean: Constraints from riverine magnesium isotope ratios

机译：现代海洋中的镁同位素收支：河边镁同位素比率的限制

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We have measured the magnesium (Mg) isotope ratios in 45 rivers including 16 of the largest rivers in the world, covering a range of geologic, tectonic and climatic drainage basin environments. The range in riverine delta Mg-26 is 2.5 parts per thousand, half the variation in terrestrial rock. Although the Mg isotopic composition of the source rock is important for small rivers, at a global scale lithology is of limited significance for Mg isotope ratios in rivers. Part of the variability at a global scale may be attributed to fractionation in the weathering environment. The rivers analysed constitute 30% of the global Mg riverine flux to the oceans and a flux weighted Mg isotope composition of global runoff has been estimated at - 1.09 parts per thousand. Even taking into account uncertainty, this is distinct from seawater at -0.82 parts per thousand.. This difference arises either from the fractionation of Mg isotope ratios in the ocean and/or a Mg budget which is not at steady state. The difference is consistent with fractionation by carbonate precipitation. In the simplest steady state scenario, where the oceanic mass balance is maintained by riverine input and hydrothermal and dolomite output, Mg isotope ratios imply a minimum dolomite Mg flux of 9% of the total output Mg flux. The implications of the distinct isotopic composition of the riverine flux from modem seawater, is that the Mg isotope ratio of seawater has probably varied outside of current analytical uncertainty. Mg isotope ratios may therefore provide a valuable new tracer in palaeo-oceanography. (c) 2006 Elsevier B.V. All rights reserved.
机译：我们已经测量了45条河流中的镁（Mg）同位素比，其中包括世界上16条最大的河流，涵盖了一系列地质，构造和气候流域环境。河流三角洲Mg-26的范围是2.5千分之一，是陆地岩石变化的一半。尽管烃源岩的Mg同位素组成对小河流很重要，但在全球范围内，岩性对于河流中Mg同位素比的意义有限。全球范围内的部分可变性可能归因于风化环境中的分级。分析的河流占全球流入海洋的Mg河流的30％，据估计，全球径流的Mg同位素加权通量为-1.09千分之几。即使考虑到不确定性，这也不同于-0.82千分之几的海水。这种差异是由于海洋中Mg同位素比例的分级和/或Mg预算处于不稳定状态而引起的。差异与通过碳酸盐沉淀的分级一致。在最简单的稳态情况下，通过河流输入以及热液和白云石的产出来维持海洋质量平衡，Mg同位素比意味着最小的白云石Mg流量为总Mg流量的9％。来自现代海水的河流通量的独特同位素组成的含义是，海水的Mg同位素比可能在当前的分析不确定性范围之外变化。因此，镁同位素比可能会提供古海洋学中有价值的新示踪剂。 （c）2006 Elsevier B.V.保留所有权利。

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