Investigation with Surface Drift-Cards to Identify the Wind Effects on the Oceanic Conditions of the Eastern Seto Inland Sea

Abstract

In this paper, we discuss wind-induced surface drift inferred from drift-card returns and its implications on the variation of the oceanic conditions in the eastern Seto Inland Sea: the Sea of Harima and Osaka Bay. The wind stress factor estimated for the average drift speed of the cards was about 0.02, which suggests the wind effect is the most dominant influ nce on the movement of the surface water in this sea. In fact, the distribution of low salinity water on the surface of Osaka Bay showed quite different patterns according to the prevailing winds. This may be due to the effect of the wind-induced current coupled with a density current which is found throughout the year. It is also noticeable that prevailing W to NW winds which blow towards the southern coast of Osaka Bay will reduce the advective speed and dispersion of low salinity water, which may result in comparatively small water-exchange in winter. On the other hand, the northward drift of the surface water which is induced by a strong southerly wind in summer possibly cause an upwelling of the bottom water on the southern coast of the Sea of Harima.