The distribution of radionuclides and some trace metals in the water columns of the Japan and Bonin trenches
The distribution of radionuclides and some trace metals in the water columns of the Japan and Bonin trenches
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DOI：
10.1016/s0399-1784(98)80031-5
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发表时间：
1998-05-01
期刊：
影响因子：
--
通讯作者：
Tsubota, H
中科院分区：
文献类型：
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作者：
Nozaki, Y;Yamada, M;Tsubota, H
本文介绍了日本海沟和小笠原海沟底部深度分别为7585 m和9750 m的两个水柱中U/Th系列Th、Pa、Ac和Pb同位素和人工沉降放射性核素（Sr-90、Cs-137和Pu同位素）以及一些微量元素（V、Zn、Cd、Cu、Mn和Ni）的第一个详细地球化学数据集。水文特性，如温度，盐度，溶解氧和营养物含量内的沟谷保持不变，在相同的水平，在底层水的西北太平洋盆地（通常类似于6000米的深度）。放射性核素的活动和大多数微量金属浓度也没有很大的不同，在上覆水在深度约5000-6000米。这意味着，这里使用的技术没有明显地检测到海水在海沟中停留期间所经历的任何化学变化。因此，海沟水与西北太平洋深海平原上的底层水通过等密度线混合而相当自由地连通。海沟沃茨中的Pu-239、Pu-240放射性很高，表明Pu正在从底部界面快速下沉的大颗粒中积极再生，这可能是由于氧化态的变化。Pb-210和Pa-231的垂直剖面显示，海沟内Pb-210和Pa-231的活度低于上覆深水沃茨中的活度，表明边界和海底清除作用对它们的海洋分布具有重要的控制作用。然而，这里研究的痕量金属没有一种明显遵循上述核素的行为。Th-228数据显示小笠原海沟内的散射，这在很大程度上归因于分析误差。然而，如果我们接受Th-228数据的分散是真实的，并且这种变化完全是由其母体Ra-228的衰变引起的，则我们将地沟水更新时间的上限设定为近似5年。(C)爱思唯尔，巴黎。
Presented here is the first detailed geochemical data set on the U/Th series Th, Pa, Ac, and Pb isotopes and artificial fallout radionuclides (Sr-90, Cs-137, and Pu isotopes), and some trace elements (V, Zn, Cd, Cu, Mn, and Ni) in two water columns of the Japan and Bonin trenches down to the bottom depths of 7585 m and 9750 m, respectively. Hydrographic properties such as temperature, salinity, dissolved oxygen, and nutrient content within the trench valley remain constant at the same levels as those in the bottom water of the Northwest Pacific basin (typically similar to 6000 m in depth). The radionuclide activities and most trace metal concentrations are also not very different from those in the overlying water at depths of around 5000-6000 m. This means that any chemical alteration which sea water undergoes during its residence within the trench was not obviously detected by the techniques used here. The suggestion follows that the trench water is rather freely communicating by isopycnal mixing with the bottom water overlying the Northwest Pacific abyssal plain. The trench waters contain high Pu-239,Pu-240 activities throughout, indicating that Pu is actively regenerating from rapidly sinking, large particles at the bottom interface, probably due to a change in the oxidation state. On the other hand, the vertical profiles of Pb-210 and Pa-231 show lower activities within the trench than those in the overlying deep waters, suggesting that the effect of boundary and bottom scavenging is significant in controlling their oceanic distributions. However, none of the trace metals studied here obviously follows the behaviour of the above nuclides. The Th-228 data show scattering within the Bonin Trench that is largely ascribable to analytical errors. If, however we accept that the scatter of Th-228 data is real and the variation is caused solely by decay of its parent Ra-228, We,,, set an upper limit of similar to 5 years for the renewal time of the trench water. (C) Elsevier, Paris.