North Pacific Intermediate Water Transports in the Mixed Water Region

Abstract

Abstract Initial mixing between the subtropical and subpolar waters of Kuroshio and Oyashio origin occurs in the mixed water region (interfrontal zone) between the Kuroshio and Oyashio. The relatively fresh water that enters the Kuroshio Extension from the Mixed Water Region is this already mixed subtropical transition water. Subtropical transition water in the density range 26.64–27.4 σθ can be considered to be the newest North Pacific Intermediate Water (NPIW) in the subtropical gyre; this density range is approximately that which is ventilated in the subpolar gyre with significant influence from the Okhotsk Sea. Freshening of the Kuroshio Extension core occurs between 140° and 165°E in the upper part of the NPIW (26.64–27.0 σθ), with the greatest freshening associated with the eastern side of the first and second Kuroshio meanders. Kuroshio Extension freshening in the lower part of the NPIW (27.0–27.4 σθ) occurs more gradually and farther to the east. There is nearly no distinction in water properties ...