Upper ocean diapycnal mixing in the northwestern Weddell Sea

Abstract

Abstract Vertical profiles of ocean temperature, salinity, dissolved oxygen concentration, and currents were obtained during austral winter 1997 from a region extending from the northeastern Antarctic Peninsula to the South Orkney Plateau in the northern Weddell Sea. From these data we estimate the spatial variation of shear-driven turbulent mixing and the mean diapycnal diffusivity (Kv) in the main pycnocline. We conclude that the mean upper ocean heat flux in the northwestern Weddell Sea is in the range 2–10 W m−2. The ocean tide provides a significant fraction of the oceanic kinetic energy in the region: tidal current speeds at the shelf break can approach 50 cm s−1 compared with mean flows of ∼5–10 cm s−1. We show that the conversion rate of barotropic to baroclinic semidiurnal tidal energy along the South Scotia Ridge, as a pathway for energy flux to the turbulent microscale, is consistent with the data-based estimates of Kv. Baroclinic tides from the ridge can penetrate into the northern Weddell Sea and may explain observed significant velocity shears in the central Powell Basin, hundreds of kilometers from significant topographic features.