Author(s): Akira Wada; Koichi Kitahara; Mitsuhito Kawanaga; Masakazu Miura; Tairyu Takano
Linked Author(s): Akira Wada
Keywords: Stratification; Annox water; Upwelling; Meteorological condition; 3D-numerical model; Tokyo Bay 1
Abstract: In the period of strong density stratification from early summer through early fall, the supply of oxygen from the sea surface to the deeper water is cut off. At the same time, organic matter decomposes near the ocean bottom, so that an anoxic water mass forms. In inner Tokyo Bay, when a northeasterly wind (directed from the inner bay toward the mouth of the bay) blows, the anoxic water mass upwells (an "Aoshio" occurs). In some cases fishes and shellfish die along the coast. Based on the results of continuous observations of water temperature, salinity and dissolved oxygen content, here we have used an improved fluid flow model to carry out 3-dimensional calculations of the water level, water temperature, salinity and flow distributions. The computational results have reproduced the observational results well. The calculations showed that upwelling of the anoxic water mass that forms during the stratified period is not only affected by the continuously blowing northeasterly wind, but also by a continuous southwesterly wind that blew several days previously. Surface water blown against the coast by this continuous southwesterly wind is pushed downward; the calculations reproduced the process by which the rising force of this previously downwelled surface water also affects the phenomenon of anoxia.