Microstructure measurements in the mid‐depth waters of the North Pacific

Microstructure measurements from the surface down to maximum depths of ∼2000 m were carried out at 28 locations in the interior of the North Pacific. Special attention was directed to the diapycnal diffusivities K ρ in the significant generation regions of the semidiurnal internal tide such as the Aleutian Ridge, the Hawaiian Ridge, and the Izu‐Ogasawara Ridge. In the profiles obtained near the Aleutian Ridge, only a few turbulent patches with ɛ ≥ 10 −9 Wkg −1 were detected and K ρ was generally less than 10 −5 m 2 s −1 . In the profiles obtained near the Hawaiian Ridge, many turbulent patches with ɛ ≥ 10 −9 Wkg −1 were observed, although K ρ was generally of the order of 10 −5 m 2 s −1 . Along the Izu‐Ogasawara Trough running in parallel with the Izu‐Ogasawara Ridge, in contrast, remarkably intense turbulent mixing (ɛ ∼ 10 −8 Wkg −1 , K ρ = 10 −4 ∼ 10 −3 m 2 s −1 ) was common throughout the observed water depth.