Frontal densification and displacement: A scenario of North Pacific Intermediate Water formation

The formation of North Pacific Intermediate Water (NPIW) requires a densification of ∼0.2-0.3 σθ through interior transformation processes. Evidence of this density anomaly is discovered on neutral density surfaces in the subarctic-tropical frontal zone (SATFZ) showing an eastward tongue of positive density anomaly coincident with a cabbeling maximum tongue. The northward displacement of the SATFZ with depth east of dateline enables the transformed dense water from overlying thermocline to sink into the northeast subtropical NPIW domain. The further southward and southwestward spreading across the subtropical gyre yields the observed distribution of NPIW.