Internal tides arise when the barotropic tide flows over uneven bottom topography and excites oscillations within the stratified interior. Along continental slopes these oscillations concentrate energy because the slope acts as a generator and reflector of internal waves. Theory and observations from Eric Kunze, University of Washington, and collaborators show that when the phase speed and slope align, energy transfers efficiently from large-scale tidal flow into internal tides, producing enhanced shear and wave breaking that drive vertical mixing. Local stratification and slope steepness critically modulate this transfer.
Generation and energy pathways
As barotropic tidal currents encounter the continental slope, they drive baroclinic motions that can radiate away as internal tides or remain trapped as slope waves. Field programs led by John N. Moum, Oregon State University, document strong turbulent overturns near shelf breaks and upper slopes coincident with internal-tide passages. Laboratory and numerical work by Andrew F. Jayne Woods Hole Oceanographic Institution and Louis St. Laurent Fisheries and Oceans Canada further demonstrate that roughness and small-scale topographic features scatter internal-tide energy into higher wavenumbers where it is more readily dissipated. The result is concentrated mixing close to the slope and a pathway for tidal energy to influence the interior ocean.
Mixing mechanisms and vertical transport
Breaking internal tides generate enhanced vertical shear and turbulent kinetic energy that erode stratification and cause vertical mixing. Carl Wunsch Massachusetts Institute of Technology and colleagues emphasize that this mixing is a key element of the ocean’s energy budget, with implications for the large-scale meridional overturning circulation. On continental slopes, mixing redistributes heat, salt, and nutrients across the pycnocline and into the coastal ocean. The efficiency of conversion from tidal energy to mixing varies strongly with latitude, tidal amplitude, and the complexity of the seabed.
Ecological and societal consequences arise because slope mixing supplies nutrients to productive continental shelves, influencing fisheries and coastal ecosystems. In regions where continental slopes border densely populated coasts, such processes also affect sediment resuspension and pollutant dispersion, with territorial relevance for coastal management. From a climate perspective, slope-driven mixing represents a localized but influential pathway by which tidal energy helps maintain deep ocean stratification and contributes to global circulation patterns.