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

The horizontal property flux induced by tides is examined by both analytica l 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. T his countergradient tidal flux is a consequence of differing boundary condi tions 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.