Figure 2. The NPIW layer analysis is done on a potential density surface (sq=26.8 kg/m3), showing mean Potential Vorticity (x10-12 (ms)-1, upper panel, < 150 shaded) and salinity change (psu, lower panel, negative values shaded, 0.02 contours dashed, 0.04 contours solid) between the two periods. The lateral PV minimum waters within the interfrontal zone, reflecting the ‘newly formed’ NPIW, are everywhere fresher, with relatively large salinity decreases of 0.04 psu where upper waters have also freshened over time (Fig. 1). This density layer is at depths of less than 300m along the Kuril Islands and deepens about 200m near the dateline along 40N as it subducts within the interfrontal zone north of the KE, and then another 200m as it crosses the KE.