Impact of the Kuroshio paths on oceanic and estuarine circulations in and around Seto Inland Sea, Japan

The estuarine circulation and associated material dispersal in Seto Inland Sea (SIS), Japan, have been reported largely affected by the intrusion of the Kuroshio water through its two narrow channels, the Bungo and Kii Channels (Figures 1 and 2). In addition, freshwater inputs and the complicated coastline, topography and over 3,000 islands could modify the influxes through nonlinear processes, and substantially enhance intrinsic variability in the estuary. In the present study, a double nested oceanic modeling framework based on ROMS downscaled from the JCOPE2 dataset is developed to examine the interaction between the estuarine and the Kuroshio water at a horizontal grid resolution of 600 m. The model result is compared with the observation of tidal and subtidal surface elevations, stratification, and velocity structure around the Kuroshio path to show a reasonable agreement. A mass flux budget analysis is then conducted by estimating the fluxes at the two channels, the freshwater discharges from the major rivers in SIS, and the precipitation/evaporation; the former has a comparable contribution to the sum of the latters. The net flux at the channels are found to be closely related to the patterns of the Kuroshio path, measured by a distance from the each channel, suggesting that the Kuroshio intrusion plays an important role in forming a seasonal variability of SIS.; Figure1: The geographical location of the Seto Inland Sea model (ROMS-L2). ; Figure2: Isobaths (white, yellow and blue lines denoting 10, 30, 100 m deep, respectively) on a monthly-averaged surface velocity magnitude in April, 2009 (color) around Seto Inland Sea.