Distribution and Circulation of the Coastal Oyashio Intrusion

Abstract

The distribution and circulation of the coastal Oyashio intrusion were examined with a CTD and shipboard ADCP survey conducted in the vicinity of the east coast of Japan in May 1994. The estimate of mixing ratios in the density range of 26.4?27.2 σ?, assuming isopycnal mixing between the pure Oyashio and Kuroshio waters, and the ADCP velocity data showed the following new results: 1) The distribution of the Oyashio water is horizontally and vertically patchy, and some of the Oyashio water patches formed mesoscale eddies with both cyclonic and anticyclonic circulations. 2) The anticyclonic Oyashio eddy had cold and low-salinity cores with low potential vorticity (PV) suggesting that the origin was the Okhotsk Sea. The cyclonic Oyashio eddy with high PV was considered to originate from the western subarctic gyre (WSAG) in the North Pacific. A new image of the intermediate Oyashio water circulation near the Oyashio?Kuroshio confluence is proposed, in which the eddies from the Okhotsk Sea and the WSAG play the significant roles.