The Role of Cabbeling and Double Diffusion in Setting the Density of the North Pacific Intermediate Water Salinity Minimum

Abstract

The top of the North Pacific Intermediate Water (NPIW) in the subtropical North Pacific is identified with the main salinity minimum in the density range 26.7-26.8. The most likely source of low salinity for the NPIW salinity minimum is the Oyashio winter mixed layer, of density 26.5-26.65. The Oyashio waters mix with Kuroshio waters in the broad region known as the Mixed Water Region (MWR), between the separated Kuroshio and Oyashio Fronts just east of Japan. It is shown that cabbeling during mixing of the cold, fresh Oyashio winter mixed layer water with the warm, saline Kuroshio water increases the density of the mixture by up to 0.07 at densities around 26.6-26.65, regardless of the mixing mechanism. Thus cabbeling accounts for about half of the observed density difference between the Oyashio winter mixed layer water and the top of the NPIW.