Current on the Edge of the Continental Shelf Northeast of Taiwan

Abstract

Data from a cruise conducted at the end of spring 1992 is presented in order to investigate the spatial structure of the countercurrent and the origin of the upwelling along the edge of the continental shelf northeast of Taiwan. The current velocity was measured by a shipboard Acoustic Doppler Current Profiler (ADCP) along the transect to examine the mean-current field. Hydrographic measurements along each transit were also performed. Based on the data, we obtained the qualitative mean-current field and its associated water characteristics. The cruise track extended from the northern coast of Taiwan to the continental shelf of the East China Sea. The measured mean current field can be divided into three regions. From the northern coast of Taiwan to the Mien-Hwa Canyon, the water flowed southeastwardly from the shelf toward the sea. This outflow could have originated from the Taiwan Strait. The current abruptly changed direction when crossing over the Mien-Hwa Canyon. In between the Mien-Hwa and North Mien-Hwa Canyons, the countercurrent dominated and flowed generally along the isobath in a southwestward or westward direction. The countercurrent spanned the entire water column with a horizontal scale of approximately 40 km. analysis of theCTD data indicated that the countercurrent originated from subsurface Kuroshio water. North of North Mien-Hwa Canyon, the flow was northward and had the same characteristic as the subsurface Kuroshio water. This indicated that the subsurface Kuroshio water transgressed the continental shelf of the East China Sea.
Additionally, the countercurrent water and the upwelling water were found to have the same characteristics as the subsurface Kuroshio water and, historically, both are permanent features. We conclude that the countercur­rent is an important factor in the origination of the upwelling found in this area.

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