A Numerical Experiment on Water and Salt Exchange through the Akashi and the Naruto Straits

Abstract

To study the relation between the water-volume exchange rates Ev and the salt-exchange rates Ez of the Akashi and the Naruto Straits in the Seto Inland Sea of Japan, we use an observed salt distribution near the straits, the calculated Eulerian velocity of the M2 current and the calculated location of about 20 000 labeled particles tracked during an M2 period. The salt-exchange rate Ez was about one-third and one-twelfth that of the water-volume exchange rate Ev for the Akashi Strait and the Naruto Strait, respectively. In general, the exchange rates of Ez and Ev do not equal each other, because Ez largely depends on the spatial distribution of salt near a strait. Therefore, Ez is not an adequate measure for the tidal exchange. We found that the salt distribution near the straits and the salt-exchange rates Ez were dependent on the deformation of a water column and that this deformation is produced not only by the velocity shear of the nonlinear tidal current but also by tide-induced transient eddies.