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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 >Cadmium isotope fractionation in seawater - A signature of biological activity
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Cadmium isotope fractionation in seawater - A signature of biological activity

机译：海水中镉同位素分馏-生物活性的标志

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Investigations of cadmium isotope variations in the oceans may provide new insights into the factors that control the marine distribution and cycling of this element. Here we present the results of Cd isotope and concentration analyses for 22 seawater samples from the Atlantic, Southern, Pacific, and Arctic Oceans. The results reveal, for the first time, large and well resolved Cd isotope fractionations in the marine environment. The majority of the seawater samples display an inverse relationship between dissolved Cd contents and isotope compositions, which range from epsilon Cd-114/110 approximate to +3 +/- 0.5 for Cd-rich waters (0.8-1.0 nmol/kg) to epsilon Cd-114/110 approximate to 38 +/- 6 for surface water with a Cd concentration of only 0.003 nmol/kg (all epsilon Cd-114/110 data are reported relative to the JMC Cd Munster standard). This suggests that the Cd isotope variations reflect kinetic isotope effects that are generated during closed system uptake of dissolved seawater Cd by phytoplankton. A few samples do not follow this trend, as they exhibit extremely low Cd contents (<0.008 nmol/kg) and nearly un-fractionated Cd isotope compositions. Such complexities, which are not revealed by concentration data alone, require that the Cd distribution at the respective sites was affected by additional processes, such as water mass mixing, atmospheric inputs of Cd and/or adsorption. Uniform isotope compositions of epsilon Cd-114/110 = + 3.3 +/- 0.5 (1 S.D.) were determined for seawater from >= 900 in depth, despite of Cd concentrations that display the expected increase along the global deep-water pathway from the Atlantic (similar to 0.3 nmol/kg) to the Pacific Ocean (similar to 0.9 nmol/kg). This indicates that the biomass, which is remineralized in the deeper ocean, is also characterized by a very constant Cd isotope composition. This observation is in accord with the interpretation that the Cd distribution in surface waters is primarily governed by Rayleigh fractionation during near-quantitative uptake of dissolved seawater Cd. (C) 2007 Elsevier B.V. All rights reserved.
机译：对海洋中镉同位素变化的研究可能会为控制该元素海洋分布和循环的因素提供新的见解。在这里，我们介绍了来自大西洋，南部，太平洋和北冰洋的22个海水样品中Cd同位素的浓度和浓度分析的结果。结果首次揭示了海洋环境中大型且解析度良好的Cd同位素分馏。大多数海水样品显示溶解的Cd含量与同位素组成之间呈反比关系，对于富含Cd的水（0.8-1.0 nmol / kg），εCd-114 / 110约为+3 +/- 0.5到epsilon对于Cd浓度仅为0.003 nmol / kg的地表水，Cd-114 / 110约为38 +/- 6（报告了所有相对于JMC Cd Munster标准的epsilon Cd-114 / 110数据）。这表明Cd同位素的变化反映了浮游植物在封闭系统吸收溶解的海水Cd期间产生的动力学同位素效应。一些样品没有遵循这种趋势，因为它们显示出极低的Cd含量（<0.008 nmol / kg）和几乎未分离的Cd同位素组成。这样的复杂性并不能单独通过浓度数据揭示出来，它要求各个位置的Cd分布受到其他过程的影响，例如水的质量混合，Cd的大气输入和/或吸附。尽管Cd的浓度显示出从Cd-114 / 110 = 110到110的全球沿深水路径的预期增加量，但仍确定了> = 900深度的海水中εCd-114 / 110 = + 3.3 +/- 0.5（1 SD）的均匀同位素组成。大西洋（约0.3 nmol / kg）到太平洋（约0.9 nmol / kg）。这表明在深海中再矿化的生物质还具有非常恒定的Cd同位素组成的特征。该观察结果与以下解释相符，即地表水中Cd的分布主要受近似定量吸收溶解海水Cd期间瑞利分馏的支配。 （C）2007 Elsevier B.V.保留所有权利。

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