The structure of flow field at Yokogan-sone seamount

The structure of flow field around a tall seamount, called Yokogan-sone, which is located to the southwest of the Nansei Islands in the East China Sea was investigated with a combination of observations and a numerical model simulation. The flow field around the seamount was preliminarily measured using an acoustic Doppler current profiler (ADCP) in May 2003. It was found that a distinct westward current flowed above the south flank of the seamount at a depth below 200 m while a eastward current attributed to the Kuroshio dominated over the seamount. Current meter moorings around the seamount were deployed for about one month in May 2004 to discriminate contributions of oceanic and tidal currents to the flow field. The results indicated that oceanic currents flowing into Yokogan-sone changed as the Kuroshio flow path dynamically moved around, and tidal currents were variable both temporally and spatially around the seamount. The Princeton ocean model (POM) was used to simulate the flow field around the seamount. The simulation was driven by steady inflow and oscillatory elevation of the sea surface, corresponding to oceanic currents and tidal elevations, respectively. The simulation results successfully reproduced the westward flow above the south flank of the seamount in spite of the dominant eastward steady flow over the structure, whereas they did not show the considerable temporal and spatial variation of strength of the tidal components