Synoptic Distribution and Circulation of the Source Waters Relating to the North Pacific Intermediate Water Formation in the Kuroshio-Oyashio Interfrontal Zone

The distribution and circulation of the Kuroshio and Oyashio waters were examined with a CTD and shipboard ADCP survey conducted in the Kuroshio-Oyashio interfrontal zone in May 1992 and May 1994, in order to investigate the process and transports of the North Pacific Intermediate Water (NPIW) formation. The mixing ratios, assuming isopycnal mixing between the pure Kuroshio and Oyashio waters, are used to examine the distribution of the Kuroshio and Oyashio waters. The Kuroshio and Oyashio water fluxes are calculated by the ADCP-referenced transport combined with the mixing ratio. The results are as follows. (1) The distribution of the Oyashio water was 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. (3) From the ADCP-referenced fluxes, the Kuroshio water 7-8 Sv (1 Sv ≡ 10⁶ m³ s^-1) and the Oyashio water 5-6 Sv were considered to form the new NPIW in the density range of 26.6-27.2 σ _θ