窒素同位体比および物質循環モデルを用いた海洋窒素循環に関する研究(2011年度日本地球化学会奨励賞受賞記念論文)

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The marine nitrogen cycle is known to often control biological activity in the ocean, because nitrogen is an indispensable nutrient for phytoplankton. Understanding the marine nitrogen cycleis very important with respect to marine biological activity. In this study, nitrogen isotopic ratios (δ^<15>N) and marine material cycle models are used to understand the marine nitrogen cycle. Here, our previous studies of nitrogen cycle in the western and central equatorial Pacific and in the Sea of Okhotsk are introduced. In the equatorial Pacific, the distributions of δ^<15>N values of nitraterevealed that surface nutrient sources are atmospheric and/or terrestrial nitrogen in the western and marine nitrogen in the central. Moreover, the time variations of δ^<15>N values in sinking particles reconstructed the transition of surface nutrient sources with transport of the fresh pool. In the Sea of Okhotsk, a marine nitrogen cycle model including nitrogen isotopes wasnewly developed in order to quantitatively understand the observed feature of winter high δ^<15>N values of sinking particles relative to the spring values. The model suggested that the nitrification with large isotopic effects causes the winter high δ^<15>N values of sinking particles. Finally, my future prospects of the nitrogen isotopic modeling are discussed.
2012-09-05