Meteorology and oceanography in the Seto Inland Sea

Abstract

The Kobe Marine Observatory has investigated meteorology and oceanography of the Seto Inland Sea(SIS) since 1920's. In this report, we describe their characteristic features in the SIS and discuss mechanism of water exchanges between the Kuroshio and the coastal area in Kii Channel. On the SIS, westerly winds prevail generally, and complex “land and sea bleezes” occur by means of its land configuration. Precipitation is less and sunshine duration is more than in any other region of Japan. Sea fogs of the SIS appear from March to August. Discharge from river is more in the eastern part than in the western part of the SIS. These elements control water mass generation, pollutant diffusion and biological activities in the SIS. In the SIS, mean eastward water transport occurs chiefly by means of westerly winds. Tidal currents prevail generally and are especially significant in straits, where the current speed is rapid and vertical mixing is very strong. The sea level is highest in Bisan Seto of the SIS, where sea surface temperature and salinity are relatively low. It is suggested that Bisan Seto seems the boundary between the western and the eastern part of the SIS. The nutrient concentration had become rich since 1930's till 1970's but thereafter it keeps the same level. In general, it is richer in the eastern part than in the western part of the SIS. Water exchanges between the SIS and the Kuroshio take place in Bungo Channel and Kii Channel. In Kii Channel, the easternmost of the SIS, it is infered that the coastal water flows out offshore in the upper layer, and the modified Kuroshio water flows into Osaka Bay in the lower layer, as supposed from observed water temperature, salinity and dissolved oxygen sections. Such mechanism can be also thought in Bungo Channel.