Abstract
Abstract. There remains much to be learned about the full range of turbulent motions in the ocean. Here we consider turbulence and overturn scales in the relatively shallow, weakly stratified, fast-flowing tidal flows of Cook Strait, New Zealand. With flow speeds reaching 3 m s−1 in a water column of ∼300 m depth the location is heuristically known to be highly turbulent. Dissipation rates of turbulent kinetic energy ε, along with the Thorpe scale, LT, are described. Thorpe scales, often as much as one-quarter of the water depth, are compared with dissipation rates and background flow speed. Turbulent energy dissipation rates ε are modest but high for oceans, around 5×10-5 W kg−1. Comparison of the buoyancy-limit Ozmidov scale LOz suggest the Cook Strait data lie for the majority of the time in the LOz > LT regime, but not universally. Also, comparison of direct and LT-based estimates of ε exhibit reasonable similarity.
Highlights
It is well-established that turbulent mixing in the ocean is intermittent and patchy
The present paper uses microstructure and overturn data to report on the stratified boundary layer response and mixing in the unique situation of Cook Strait as an aid extending our knowledge around oceanic turbulence
(ii) How does the Thorpe scale compare with the Ozmidov scale? (iii) Following from this, can a fixed ratio be assumed and so allow estimation of ε? (iv) How does the turbulence compare with other straits?
Summary
It is well-established that turbulent mixing in the ocean is intermittent and patchy (see Waterhouse et al, 2014 for a synthesis). In a 1999 paper reviewing the first shear probe measurements of oceanic turbulence, Stewart and Grant (1999) described the flows in Seymour Narrows (Discovery Passage, Canada) as sustaining Reynolds numbers (Re) amongst the “largest in the universe”. True or not, it is a useful benchmark and discussion point. The present paper uses microstructure and overturn data to report on the stratified boundary layer response and mixing in the unique situation of Cook Strait as an aid extending our knowledge around oceanic turbulence. (ii) How does the Thorpe scale compare with the Ozmidov scale? (iii) Following from this, can a fixed ratio be assumed and so allow estimation of ε? (iv) How does the turbulence compare with other straits?
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
