Strong vertical mixing in the Urup Strait

Abstract

[1] Microstructure measurements were conducted in one of the Kuril Straits in the summer of 2007. Over the course of 1 day of repeated observations across the Pacific side of the steep sill of the Urup Strait, extremely strong mixing was observed during periods of Pacific-ward (down-sill) flows and during the transition from Pacific-ward to Okhotsk-ward (up-sill) flows, with a turbulent energy dissipation rate ɛ of 10−6 to 10−5 W kg−1 and vertical diffusivity of 10−1 to 5 × 10−1 m2 s−1. During the period of strong mixing, we observed homogeneous layers with a thickness of 300–600 m and potential density of 26.6–26.7 σθ, occupying the entire water column in one case. High values of ɛ within this layer indicate the injection of diapycnal flows from the upper and lower layers, possibly contributing to southward intrusion of intermediate water into the subtropical gyre.