Meridional transport of the North Pacific Intermediate Water in the Kuroshio-Oyashio interfrontal zone

Abstract

Meridional transport and origin of the North Pacific Intermediate Water (NPIW) in the Kuroshio-Oyashio interfrontal zone (K/O zone) were examined using hydrographic and velocity data with LADCP (Lowered Acoustic Doppler Current Profiler) along 37°N in the northwestern Pacific. Dominant northward transports were observed west of the Shatsky Rise (coast-157°E) in both upper (26.6-27.0Σθ) and lower NPIW (27.0-27.5ΣQq). In the upper NPIW, northward transports of 4.3 Sv which consist of the dominant Kuroshio (3.2 Sv) and small Oyashio component (1.1 Sv) were observed, suggesting that the upper NPIW in the K/O zone was formed by the mixing between the southward Oyashio water across the Oyashio Front and the Kuroshio water bifurcated from the Kuroshio Extension. In the lower NPIW, 9.4 Sv of northward transports (Kuroshio 5.5 Sv and Oyashio 3.9 Sv) were observed, suggesting that the lower NPIW in the K/O zone was maintained by the northward transport of the NPIW formed near the Kuroshio Extension.