Blocking of the Kuroshio by the continental shelf northeast of Taiwan

Abstract

In an area immediately northeast of Taiwan where in April 1989 an on‐shelf intrusion of the Kuroshio was observed, hydrographic observations from August 1991 indicate a blocking of the Kuroshio at the continental shelf break. It appears that the Kuroshio approaches the shelf break as a near‐bottom current and is deflected. The deflection apparently gives rise to a countercurrent along the shelf break which was observed by a buoy‐mounted acoustic Doppler current profiler deployed within a month of the hydrographic survey. The on‐shelf hydrographic distribution accompanying the deflection exhibits a field of near‐bottom eddies dominated by a particularly well organized large pool downstream and to the right of the approaching Kuroshio but well separated from the Kuroshio. The hydrographic properties of the pool are similar to those of the uplifted Kuroshio subsurface water observed in April 1989, suggesting that it may be the remnant of the Kuroshio subsurface water that intruded during the previous winter. A theory of the blocking is put forth in terms of the approach of a bottom current toward a step rise of the bottom in a two‐layered, reduced‐gravity ocean model in which the thickness of the current exceeds the rise in topography. The theory predicts a complete blocking that features a flow deflection in front of the step and the presence on the step of a preexisting region of high baroclinic pressure, similar to the observation. The theory also predicts approximately correctly the track of the isotherm that bounds the large pool on the side facing the on‐rushing Kuroshio.