Examination on the Relationship between Bottom Sediment Transport and Baroclinic Structure by Numerical Model in Minamata Bay

Abstract

We have been attempting to develop the numerical model for mercury fate in Minamata Bay and Yatsushiro Sea. In this paper we compared numerical results of bottom sediment transport from the bay to the outer sea area for one year with and without sea water and freshwater stratification. As a result, it was clarified that long term bottom sediment transport was determined by both of barotropic currents and baroclinic ones. Thus, accurate numerical model for particulate mercury fate must take into account baroclinic structure in actual coastal area due to freshwater inflow.

A Novel Particle Size Classification-Based Method for Analyzing Total Mercury Concentration Distribution of Sediment in the Yatsushiro Sea

“…Overall, in the horizontal direction, the T-Hg concentration became smaller and smaller along A and B lines from the sampling point Y28, indicating the mercury transport from Minamata Bay to the Yatsushiro Sea. The sediment migration along line A is considered to be mainly affected by barotropic current, while the sediment migration along line B mainly influenced by baroclinic current, consistent with the findings by Yano et al 19) . In the vertical direction, the T-Hg concentration increased first and then decreased overall.…”

Analysis of Distribution and Migration of Mercury in Sediment in the Yatsushiro Sea Based on the Classification Experimental Method

“…Meanwhile, mercury exceeding 0.5 ppm is distributed within about 100 km 2 southwest direction from Minamata Bay, while it is only distributed within about 55 km 2 northeast direction from Minamata Bay. Southwest direction from Minamata Bay is considered to be mainly affected by barotropic current, while northeast direction by baroclinic current 17) . Meanwhile, the bottom slope in the southwest direction from Minamata Bay is generally smaller than that in the northeast direction (Fig.…”