| Co-Investigator(Kenkyū-buntansha) |
NAKATSUJI Keiji Osaka University, Graduate School of Civil Engineering, Professor, 工学研究科, 教授 (10029324)
SAKAMOTO Wataru Kyoto University, Graduate School of Agiculture, Professor, 農学研究科, 教授 (50013587)
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| Research Abstract |
We studied transport of nutrients and primary production in semi-enclosed seas. Study fields extended over Osaka Bay - Kii Channel System, Ise Bay, Tokyo Bay, and Gokasho Bay. In the study we put emphasis on the behavior of hypoxic water masses, which have high concentration of nutrients. This study was composed of following four sub themes.
1. Budget of N (nitrogen) and P (phosphorus) in Osaka Bay :
A large amount of nutrients flowed into the Seto Inland Sea from the outer ocean in the summer. To establish N and P budget in Osaka Bay - Kii Channel System, we measured N and P fluxes in the system over the year. In case of P, Ca. 10 to 20 % of the anthropogenic loading is buried in the bottom sediment, and the rest of P is transported to the outer ocean by water exchange. In contrast, over than a half of N loading is missed in Osaka Bay. This suggests that there is a large flux of N from the sea to the air by denitrofication in the bay.
2. Interaction between the flow structure and N/P tra
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Flow, especially upwelling is strongly related to the primary production. In this study, we revealed vertical profile of the upwelling velocity in the semi-enclosed sea. Benthic hypoxic water mass contains nutrients with high concentration, and its N/P ration is lower than that in the surrounding water. Location of the hypoxic water mass oscillates with the intrusions of oceanic water into the bay. When a strong intrusion occurs, the hypoxic water mass is lifted and forms "subsurface hypoxic water mass". At the same time the hypoxic water mass is squashed and extends thinly. A part of the water mass is transported to the out of the bay. This process induces selective transport and elimination of P from the bay. Main part of the behavior of the hypoxic water mass is explained by physical processes.
3. Spatial and temporal distribution of primary production in semi-enclosed seas :
Spatial and temporal distribution of primary production is very difficult to measure by using conventional methods. We developed a method to estimate them.
4. Estuarine circulation under the effect of Earth's rotation :
Estuarine circulation is a vertical circulation driven by the horizontal density gradient. We studied rotational effect on this circulation and found that anti-cyclonic circulation is induced in the upper layer in ROFIs. Less
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