Tracers of chemical scavenging in the ocean: boundary effects and large-scale chemical fractionation
Tracers of chemical scavenging in the ocean: boundary effects and large-scale chemical fractionation
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海洋中化学清除的示踪剂：边界效应和大规模化学分馏
DOI：
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发表时间：
1988
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影响因子：
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通讯作者：
M. Bacon
中科院分区：
文献类型：
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作者：
M. Bacon
天然放射性衰变系列中的几种核素在海洋水柱中表现出强烈的非保守性，因为它们在固-溶液界面上被吸收到沉积物中。这一去除过程通常被称为清道夫，被认为对控制海洋中许多重金属和其他痕量物质的行为很重要。海水中放射性不平衡的测量。清扫速率的估算。结果表明，清扫清除时间与流域内横向混合时间相当。因此，被清除的示踪剂的分布应该对其汇的空间分布敏感，这一点已被观察证明，最明显的是在210Pb的情况下。~(210)Pb的分布表明，边界，特别是海洋边缘的吸收加强，控制作用很强。这一结论已被沉积物圈闭和沉积物柱中~(210)Pb积累量的测量所证实。在231Pa.也观察到了类似的海洋边缘加强的清扫现象。另一方面，230的研究表明，它向沉积物的输送主要是由下沉颗粒的局部通量引起的。因此，我们设想了两条清除的传输路径，一条是由于边缘的强化吸收而具有较强的水平分量，另一条是由于颗粒通量而具有较强的垂直分量。重要的大规模化学分馏是由于元素在这两条路径之间的不同分配而产生的，最好的例证是230和231Pa的比较研究。模式计算表明，水平混合速率和颗粒通量是控制活性化学物质在内洋中上层沉积物和大洋边缘半远洋沉积物之间分配的重要变量。这种分配程度随时间的变化可以记录为通过沉淀柱的230/231Pa值的变化。
Several nuclides in the natural radioactive decay series display a strong non-conservative behaviour in the oceanic water column because of their removal to the sediments by uptake at the solid—solution interface. This removal process is commonly referred to as scavenging, and it is believed to be important in governing the behaviour of many heavy metals and other trace substances in the ocean. Measurements of radioactive disequilibrium in seawater yield estimates of the rate at which scavenging occurs. Results show that removal times by scavenging are comparable to within-basin lateral mixing times. It follows that the distribution of the scavenged tracers should be sensitive to the spatial distribution of their sinks, and this has been demonstrated by observation, most notably in the case of 210Pb. The distribution of 210Pb suggests a strong control by intensified uptake at boundaries, especially at the ocean margins. This conclusion has been confirmed by sediment traps and by measurements of 210Pb accumulations in the sediment column. A similar phenomenon of intensified scavenging at ocean margins has been observed for 231Pa. Studies with 230Th, on the other hand, show that its delivery to the sediments is mainly caused by the local flux of sinking particles. Thus two transport pathways for removal by scavenging are envisioned, one with a strong horizontal component due to the intensified uptake at the margins and the other with a strong vertical component due to the particle flux. Important large-scale chemical fractionations, best illustrated by comparative studies of 230Th and 231Pa, are produced by differential partitioning of elements between these two pathways. Model calculations suggest that horizontal mixing rate and particle flux are important variables controlling the partitioning of reactive chemical substances between pelagic sediments of the interior ocean and hemipelagic sediments of the ocean margins. Changes in the extent of this partitioning through time may be recorded as changes in the 230Th/231Pa ratio through the sediment column.