Downwelling then upwelling again of the upwelled Kuroshio water in the southern East China Sea

Abstract

As has been well known for several decades, the subsurface Kuroshio waters upwell onto the East China Sea when the Kuroshio impinges on the continental shelf northeast of Taiwan. Based on hydrological and geochemical data, our previous study demonstrated that the upwelled Kuroshio waters downwell then upwell again northwest of Taiwan in August. A subsequent effort attributed this complex phenomenon to varying vorticity or the Rossby number at the study area, which encompasses two strong currents, i.e., the Kuroshio and the Taiwan Warm Current. Moreover, downwelling-favorable winds coincided with the observation period. This study demonstrates that the above phenomenon does not occur in the northern Taiwan Strait, but appears to surface outside of the strait during all seasons. In general, downwelling of previously upwelled Kuroshio waters from the east brings down waters from the surface, explaining why the recipient bottom waters show a horizontal maximum temperature but a minimum salinity, αt and NO3 + NO2. The downwelled waters subsequently upwell again. Since the recipient near-surface waters arise from the depth, there exists a horizontal minimum in temperature but a maximum salinity, αt and NO3 + NO2 is found. However, whether wind patterns play a critical role in generating these vertical water movements remains unclear. © 2011 by the American Geophysical Union.