Tidal mixing in the southern Weddell Sea: results from a three-dimensional model

A three-dimensional primitive equation ocean model is used to study themagnitude and distribution of tidal mixing in the southern WeddellSea. The contributions of (a) semidiurnal barotropic constituentsM2 and S2, (b) internal tides, and (c)diurnal barotropic tides are considered. Computedelevation co-tidal charts are generally consistent with our knowledgeand observations for the region. The model reproduces maximum semidiurnal tidalelevations of about 1.6 m and 1.0 m for M2 and S2, respectively. Aninternal tide of moderate strength is generated over the slope,propagating in the along-slope direction but rapidly dissipating. Onthe continental shelf, a thick benthic boundary layer (150 m) developsdue to the proximity of the critical latitude for the M2constituent. Typical M2 and S2 baroclinictidal currents at the shelf break are 10 cm/s and 6 cm/s, respectively.In general, the tidal currents produce strong mixing in the bottom boundary layer at the shelf breakand on the shelf leading to high vertical eddy viscosity/diffusivitycoefficients of up to 0.1 m2/s. Both summer and winter stratification are investigated;increased mixing near the surface is found in summer. The model results suggestthat tides contribute significantly to the turbulent mixing at theshelf break of the southern Weddell Sea.