In this paper, model experiments of discharged water and numerical calculations were carried out in order to clarify the behavior of the discharged water from the ocean nutrient enhancer named TAKUMI. The results of the experiments and the calculations show that temperature stratifications prevent the discharged water from sinking to the bottom, and the numerical calculations can estimate the behavior of the discharged water from "TAKUMI".
Recently, overfishing and environmental degradation are fundamental issues of fisheries and aquaculture in the world (Schrank, 2003). One of the solutions is the marine enhancement stock using deep ocean water (DOW) which is renewable energy resource with great potential. Marino Forum 21 project has developed the Ocean nutrient enhancer (ONE) named "TAKUMI". TAKUMI is the floating structure which pumps up nutrient-rich DOW, mixes the DOW with surface seawater, and discharges the mixed water into the euphotic layer to develop fishery ground. TAKUMI was set in the center of Sagami Bay in Japan, and has been operating since July 2003 (Ogiwara et al., 2001, Ouchi, 2003). The behavior of the discharged water from TAKUMI is one of the most important topics to enhance the marine stock effectively, but it is difficult to know that because the sea has temperature stratifications. Ouchi et al., (2001) carried out scale model experiments in the water tank with salinity stratifications to design for TAKUMI. In that paper, they reported that the discharged water from TAKUMI would spread in the area, which is about 12 m in thickness and 510 m in diameter, for 14 hours. In addition, ocean observations have been performed around TAKUMI since 2003. However the behavior of the discharged water into water with temperature stratifications is not still clear in detail. There are few investigations about discharged DOW considering temperature stratifications.