Distribution and formation of North Pacific Intermediate Water

Abstract

The North Pacific Intermediate Water (NPIW) is examined with respect to its overall property distributions. These suggest that NPIW is formed only in the northwestern subtropical gyre; that is, in the mixed water region between the Kuroshio Extension and Oyashio front. Subsequent modification along its advective path increases its salinity and reduces its oxygen. Waters from the Oyashio, Kuroshio, and the Tsugaru Warm Current influence the mixed water region, with a well-defined local surface water mass formed as a mixture of the surface waters from these three sources. Significant salinity minima in the mixed water region are grouped into those that are directly related to the winter surface density and are found at the base of the oxygen-saturated surface layer, and those that form deeper, around warm core rings. Both could be a source of the more uniform NPIW to the east. -from Author