On the tide-induced property flux: Can it be locally countergradient?

The horizontal property flux induced by tides is examined by both analytical and numerical models. It is found that this flux is highly heterogeneous in the vertical and may be directed up the mean gradient near the bottom. This countergradient tidal flux is a consequence of differing boundary conditions satisfied by velocity and property fields, and hence a robust feature. The corresponding tidal diffusivity is substantial where tides are strong and hence potentially important in the mean property balance.