Residence times and the removal mechanisms of trace elements in the ocean

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  • 海洋における微量元素の滞留時間と除去のメカニズム
  • カイヨウ ニ オケル ビリョウ ゲンソ ノ タイリュウ ジカン ト ジョキョ

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Abstract

The overall residence time of elements in the ocean water is controlled by a number of processes. In general, transport processes from source to sink as well as phase transformation within the ocean appear to control their oceanic residence times. Their relative importance depends on the residence time of the element in relation to oceanic mixing time. The dependence of residence times on the source and sink functions are derived using a diffusion-advection-phase transformation model. This model can be used to predict the oceanic response to the various types of source functions of materials; for example, supply of pollutants caused by industrialization. A particular application of the model is made for the distribution of 210Pb. The 210Pb residence time calculated in the surface and subsurface ocean depends on the thickness of the layer, i. e. the size of reservior. This can be best understood in terms of downward transport of the atmospherically derived 210Pb by settling of particles bearing 210Pb. In the deep ocean however, the dependence of 210Pb resideece time on the size of reservior becomes obscure due to in-situ production from 226Ra, possible regeneration of particulate 210Pb originated from the above waters and in-situ scavenging by settling particulate matter. Available data are insufficient to deduce the actual removal mechanisms, and hence to test the validity of several models presented by previous workers for the removal of 210Pb and the related trace metals in the deep sea. Information on age characteristics of reactive radionuclides present in the ocean and leaving out of the ocean should help to clarify them.

Journal

  • Chikyukagaku

    Chikyukagaku 12 (1), 27-36, 1978

    The Geochemical Society of Japan

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