Evaluation method of marine biological activity studied with natural radioisotopes

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  • 天然放射性核種による海洋における生物活動の評価法について
  • テンネン ホウシャセイカクシュ ニ ヨル カイヨウ ニ オケル セイブツ カツドウ ノ ヒョウカホウ ニ ツイテ

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Using natural radionuclides as tracers and the Settling Model for the removal of insoluble chemical elements in seawater first applied by Tsunogai and Nozaki (1971), my group has studied the particulate fluxes of chemical constituents including carbon in the ocean. The results and the concept of the settling model, however, have been neglected in the recent review on the use of short-lived Th isotopes for the particulate flux of organic carbon written by Okubo and Nozaki (2003). In this paper, the works missing in the review are summarized, which bring out different conclusions on this topic as given below. The behavior of sparingly soluble radionuclides in the ocean is well depicted by an improved settling model, the Train - Passenger Model. The radionuclides behave like passengers of trains which are settling down with high speeds, and trains consisting mostly of aggregated organic debris. Thus, there is no direct quantitative relation between the radioactive disequilibria of the nuclides and the organic carbon flux, but there may be some proportionality under some restricted conditions. The wisest way of use of these radionuclides is to evaluate the collection efficiency of sediment traps by observing the particulate flux of these nuclides with sediment traps and the degree of radioactive disequilibria in the surface mixed layer. Of course, we must examine many factors relating to the collection efficiencies such as their dependence on the particle size or sinking velocity, the deviation from a steady state for the radioactivity in seawater, etc. On the other hand, Okubo and Nozaki (2003) have reviewed this topic using a priori the original Scavenging Model which was already denied by Nozaki et al. (1981) and the problems given by them are mostly due to the self-contradiction arising from use of the model.


  • Chikyukagaku

    Chikyukagaku 37 (4), 157-164, 2003

    The Geochemical Society of Japan

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