Turbulent mixing in Barrow Strait

Data collected in Barrow Strait during April and May 1995 indicate that turbulence can occur throughout the water column, with the most energetic turbulence being associated with strong currents during spring tides. In the surface mixed layer (SML) under the first-year, land-fast ice, the average effective vertical diffusivity was proportional to current speed, with mean values ranging up to 0.02 m2 s-1. Current speeds in the SML during tidal maxima sometimes exceeded 20 cm s-1 but turbulent stress levels remained low because the ice undersurface was hydrodynamically smooth. An asymmetry observed in under surface drag during the tidal cycle is associated with changes in eddy viscosity, possibly in response to the advection of a horizontal salinity gradient in the SML in this region. In the sharp halocline (N≈15–20 cycles h-1) at the base of the SML, mixing was often too weak to transport heat, salt, and other scalars vertically. During such periods the halocline acts as a barrier to the transport of properties, such as nutrients, from the deeper water to the surface. Within the deeper, less-stratified, water (N≈3–5 cycles h-1), energetic mixing frequently occurred, and was modulated by both the spring/neap tidal variability and within each tidal cycle. The water column was, on average, fresher than observed in previous spring measurements from this area, suggesting interannual variability in the Archipelago hydrography.