Internal tide on the Yermak Plateau in the Arctic Ocean

Data on current velocity in the upper oceanic layer are analyzed. The data were obtained on the Yermak Plateau at a latitude of about 82 degrees N during a 52-day drift of a buoy equipped with an acoustic Doppler current profiler (ADCP). The amplitude of the diurnal barotropic tide on the plateau reaches 25 cm/s, and the level of the total spectrum of internal waves is high compared to that in the other regions of the Arctic basin, despite the fact that the latitude exceeds the critical one for the most intense lunar semidiurnal internal tide. Outbursts of three types of oscillations in the current velocity-barotropic diurnal, baroclinic semidiurnal, and baroclinic low-frequency-manifest themselves in a drift path rather simultaneously. This is explained by the association of the outbursts with sharp bottom rises. The barotropic diurnal tide interacts with the plateau relief nearly at resonance, increases, and generates residual currents of negative vorticity around the bottom rises; in this way, it opens the medium to the free propagation of the lunar semidiurnal internal tide. In these locations, the internal tide is generated near the bottom, rises upward, and largely disintegrates near the ocean's surface, thus mixing up the upper layer of the ocean. The bottom rises also create the conditions for the existence of low-frequency baroclinic waves. These waves actively exchange the energy with the internal tide.