Transport of North Pacific intermediate water in the Kuroshio–Oyashio interfrontal zone

Abstract We have estimated the volume transports of the subarctic and subtropical waters in the intermediate layer in the potential density range of 26.6–27.5 σ θ in the Kuroshio–Oyashio interfrontal zone, using hydrographic data and directly measured velocity data with a LADCP from the R/V Soyo-maru cruise performed in May–June 1998. The subarctic water flowing into this area along the Oyashio near Hokkaido (5.2 Sv) and from the subarctic front (2.0 Sv) merged with the subtropical water (13.5 Sv) along the Kuroshio near Japan and formed 20.7 Sv of North Pacific intermediate water (NPIW). NPIW mainly flowed eastward along the Kuroshio Extension, and the transport across 158°E was about 18.8 Sv (7.2 Sv of subarctic water and 11.6 Sv of subtropical water). Another 2.3 Sv of the subtropical water were transported farther northward across 39°N. These results support the hypothesis that NPIW is mainly formed along the Kuroshio Extension.