Determining coastal mixing rates using radium isotopes
Determining coastal mixing rates using radium isotopes
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DOI：
10.1016/s0278-4343(00)00054-6
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发表时间：
2000-11-01
影响因子：
2.3
通讯作者：
Moore, WS
中科院分区：
文献类型：
--
作者：
Moore, WS
沿海水域含有四种镭同位素的溶解活性升高。这些升高的活动是通过从颗粒表面解吸Ra和富含Ra的海底地下水的输入而产生的。在海岸附近，Ra的输入被每个Ra同位素流向开阔海洋的流量所平衡。其中两个Ra同位素在到达大陆架边缘之前几乎完全衰变；另外两个几乎没有衰变。这些衰减率的差异对水在陆架上的运动和混合模型提供了强有力的限制。这些模型被用来评估控制镭出口的因素。了解控制镭出口的因素有助于评估调节沿海海洋中其他溶解成分的通量的物理过程。在这篇文章中，我使用了在南大西洋八号垂直层结条件下进行的观测。长寿命Ra-226和Ra-228的近海断面表明，涡旋扩散控制了它们在距海岸50公里范围内的分布。该地区Ra-223和Ra-224的短寿命分布产生的涡旋扩散系数为360-420m(2)S(-1)。Ra-226和Ra-228的离岸通量来自它们的跨陆架活动梯度和涡旋扩散系数，需要大量的地下水排放来平衡Ra的去除。(C)2000爱思唯尔科学有限公司。保留所有权利。
Coastal waters contain elevated dissolved activities of four radium isotopes. These elevated activities arise through desorption of Ra from particle surfaces and the input of submarine groundwaters enriched in Ra. The input of Ra near the coast is balanced by a flux of each Ra isotope toward the open ocean. Two of the Ra isotopes decay almost completely before they reach the edge of the continental shelf; the other two decay hardly at all. These differences in decay rates provide a powerful constraint on models of water movement and mixing on the shelf. These models are used to assess the factors that control the export of radium. Understanding the factors that control the export of radium allows an assessment of physical processes that regulate fluxes of other dissolved constituents in the coastal ocean. In this paper I use observations that were made during vertically stratified conditions in the South Atlantic Eight. Offshore transects of the long-lived Ra-226 and Ra-228 indicate that eddy diffusion controls their distributions within 50 km of shore. The short-lived Ra-223 and Ra-224 distributions in this region yield an eddy diffusion coefficient of 360-420 m(2) s(-1). The offshore fluxes of Ra-226 and Ra-228 derived from their across-shelf activity gradients and the eddy diffusion coefficient require a substantial volume of groundwater discharge to balance Ra removal. (C) 2000 Elsevier Science Ltd. All rights reserved.