Heavy nickel isotope compositions in rivers and the oceans
Heavy nickel isotope compositions in rivers and the oceans
复制标题
DOI：
10.1016/j.gca.2013.12.007
复制
发表时间：
2014-03-01
影响因子：
5
通讯作者：
Vance, D.
中科院分区：
文献类型：
--
作者：
Cameron, V.;Vance, D.
镍是一种具有生物活性的微量金属，其在海洋中的溶解浓度深度剖面显示出类似营养物的行为。如果镍在表层海洋中从溶解相中明显地被去除，并返回到深海中，这与同位素分馏有关，那么镍同位素可能能够对所涉及的精确地球化学过程产生限制。在这里，我们提出了第一个海水镍同位素数据沿着与数据的溶解相的河流，镍的主要来源之一的海洋。河流的溶解相表现出显着的变化在Ni浓度和三角洲Ni-60：从2.2至35 nmol kg（-1）和+0.29至+1.34千分之一，分别。对河流进行镍同位素分析得出的最显著的结果是，它们比大陆上硅酸盐岩石的范围重得多（三角洲Ni-60高达千分之一），这一发现与其他过渡金属同位素系统的结果类似。如果这里提供的数据接近于全球河流通量的代表，他们建议每年向海洋输入的Ni为3.6 x 10（8）摩尔，排放和浓度加权的Δ Ni-60平均值为+0.80ppm。Ni同位素和浓度之间的关系与其他过渡金属同位素系统的关系相似，其中主要的控制因素被认为是溶解相和颗粒之间的同位素分配，无论是在风化环境中还是在运输过程中，与河流形成鲜明对比的是，海水数据集非常均匀，整个数据集的2SD只有分析再现性的两倍。第二个主要特征是海水的镍同位素明显比河流重。三角洲的平均Ni-60为1.44 +/- 0.15千分之一（2SD），29个海水分析中只有2个的Ni同位素组成比最重的河流轻。缺乏与表层海洋中镍浓度下降相关的同位素变化表明，表层和深海之间的镍循环与明显的同位素分馏无关。同位素数据也提出了一个质量平衡问题。镍的主要输出从海洋（吸附到铁锰氧化物）似乎是类似的同位素组成的溶解相，但河流输入是轻于溶解池。这种观察要么需要其他同位素重的输入，要么需要同位素轻的输出。进一步大的投入，以上溶解的河流来源，似乎需要我们所知道的元素预算，但同位素质量平衡表明，这样的投入需要同位素比河流溶解负荷和镍的成岩同位素组成重得多。(C)2013爱思唯尔有限公司保留所有权利。
Nickel is a biologically-active trace metal whose dissolved concentration depth profiles in the ocean show nutrient-like behaviour. If the pronounced removal of nickel from the dissolved phase in the surface ocean, and its return in the deep, is associated with an isotopic fractionation nickel isotopes may be able to yield constraints on the precise biogeochemical processes involved. Here we present the first nickel isotope data for seawater along with data for the dissolved phase of rivers, one of the principal sources of nickel to the oceans.The dissolved phase of rivers exhibits substantial variability in both Ni concentration and delta Ni-60: from 2.2 to 35 nmol kg(-1) and +0.29 to +1.34 parts per thousand, respectively. The most striking result from the nickel isotope analyses of rivers is that they are substantially heavier (by up to 1 parts per thousand for delta Ni-60) than the range for silicate rocks on the continents, a finding that is analogous to that for other transition metal isotope systems. If the data presented here are close to representative of the global riverine flux, they suggest an annual input of Ni to the oceans of 3.6 x 10(8) moles, and a discharge-and concentration-weighted delta Ni-60 average of +0.80 parts per thousand. The relationship between Ni isotopes and concentrations shows similarities with those for other transition metal isotope systems, where the main control has been suggested to be isotopic partitioning between the dissolved phase and particulates, either in the weathering environment or during transport.In stark contrast to the rivers, the dataset for seawater is very homogeneous, with 2SD of the entire dataset being only twice the analytical reproducibility. The second main feature is that seawater is distinctly heavier in Ni isotopes than rivers. The average delta Ni-60 is 1.44 +/- 0.15 parts per thousand (2SD), and only 2 of the 29 seawater analyses have a Ni isotopic composition that is lighter than the heaviest river. The lack of an isotopic shift associated with the drawdown of nickel concentrations in the surface ocean suggests that the cycling of nickel between the surface and deep ocean is not associated with a pronounced isotopic fractionation. The isotopic data also present a mass balance problem. The main output of nickel from the oceans (sorption to Fe-Mn oxides) appears to be similar in isotopic composition to the dissolved phase, yet the riverine input is lighter than the dissolved pool. This observation either requires other inputs that are isotopically heavy, or an output that is isotopically light. Further large inputs, over and above the dissolved riverine source, appear to be required by what we know of the elemental budget, but the isotopic mass balance suggests that such an input needs to be isotopically much heavier than both the riverine dissolved load and the lithogenic isotopic composition of nickel. (C) 2013 Elsevier Ltd. All rights reserved.