Waves on the pycnocline, called internal waves, are ubiquitous in Pelorus Sound. They propagate at and involve vertical displacements of the pycnocline through . They are often generated by the tide, in which case they are called internal tides. They play an important part in driving flow and horizontal exchange in bays off the main channel. For example, current meter records at the entrance to Beatrix Bay show a significant semi-diurnal component with velocities up to . This is not simple, uniform tidal flow in and out of the bay because its amplitude does not follow a spring-neap cycle and there is a phase difference of several hours between the surface and the bottom.