DIURNAL TIDES NEAR THE YERMAK PLATEAU

Recent current measurements obtained from drifting platforms over the Yermak Plateau in the eastern Arctic Ocean confirm that the plateau is a region of greatly enhanced diurnal tidal currents. Modulation of the diurnal currents is clearly related to the plateau topography, as has been previously proposed. We show, however, that temporal variability due to spring-neap modulation must also be considered in interpreting records from drifting platforms. We review simple models of tidal current amplification in this region and find that the previous assumption of near-resonant, barotropic shelf waves propagating around the plateau's entire perimeter is inconsistent with the true topography. Instead, we propose that the diurnal variability is due to topographic shelf waves at the K1 and O1 tidal frequencies that are generated at points on the plateau's perimeter where the waves' group velocities are near zero. Observed cross-slope variations in ellipticity, orientation, and magnitude of tidal oscillations are consistent with the presence of topographic waves generated in this manner. The topographic enhancement of the diurnal tide near the Yermak Plateau has important consequences for the sea ice cover, hydrography, and general circulation of this region. For example, the stress divergence applied by the tidal currents at the ice base greatly exceeds the typical divergence of the surface wind stress, and tides may therefore be important to local ice deformation. The strong cross-slope tidal currents also appear to be responsible for the production of high-frequency internal wave packets, which are associated with energetic diapycnal mixing in the pycnocline. We also consider the possibility that tidal rectification is responsible for a mean current transporting Atlantic Water clockwise around the plateau.