The magnesium isotope budget of the modern ocean: Constraints from riverine magnesium isotope ratios
The magnesium isotope budget of the modern ocean: Constraints from riverine magnesium isotope ratios
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DOI：
10.1016/j.epsl.2006.07.037
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发表时间：
2006-10
影响因子：
5.3
通讯作者：
E. Tipper;A. Galy;J. Gaillardet;M. Bickle;H. Elderfield;E. A. Carder
中科院分区：
文献类型：
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作者：
E. Tipper;A. Galy;J. Gaillardet;M. Bickle;H. Elderfield;E. A. Carder
我们测量了45条河流中的镁（Mg）同位素比值，其中包括世界上最大的16条河流，涵盖了一系列地质，构造和气候流域环境。河流δ 26 Mg的变化范围为2.5‰，是陆源岩石变化的一半。虽然镁同位素组成的源岩是重要的小河流，在全球范围内的岩性是有限的意义，在河流中的镁同位素比值。在全球范围内的变化的一部分可能是由于风化环境中的分馏。所分析的河流占全球流入海洋的Mg河流通量的30%，全球径流的通量加权Mg同位素组成估计为-1.09 ‰。即使考虑到不确定性，这也不同于-0.82 ‰的海水。这种差异产生的分馏镁同位素比值在海洋和/或镁预算，这是不稳定的状态。这种差异与碳酸盐沉淀的分馏作用一致。在最简单的稳定状态的情况下，海洋质量平衡维持河流输入和热液和白云石输出，镁同位素比值意味着最低白云石镁通量的9%的总输出镁通量。从现代海水的河流通量的不同同位素组成的影响，是海水的镁同位素比可能已经改变了目前的分析不确定性之外。因此，镁同位素比值可能提供一个有价值的新的古海洋学示踪剂。
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 δ26Mg is 2.5‰, 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‰. Even taking into account uncertainty, this is distinct from seawater at −0.82‰. 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 modern 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.