Sedimentological Characters in Isahaya Bay by Analysis of Radium Isotope Ratio, Isahaya Bay, Japan

The movements of the water masses are evaluated by Ra-228/Ra-226 (radioisotope ratio) in the open sea. However, the study on the water's movement in the littoral region based on this ratio is few, because the supply process of Ra-228 is complex. The purposes of this study are explication of the sedimentological characters and the seawater's circulation in the Isahaya bay based on the radium isotope, benthic foraminifers and topography. The erosion and redeposition, that are related with the inflow of the open seawater, are recognized from central to outer area in the southern part of the bay. The radioisotope ratio suggests that the stagnation in the seawater circulation is only present in the front of north drain gate on the dyke in Isahaya reclaimed land.