Anomalous Diurnal Tidal Currents on the Yermak Plateau

摘要

Recent observations made over the Yermak Plateau, a 100 x 200 km submarine feature northwest of Svalbard, show that ocean currents in that area are dominated by diurnal tidal currents although semidiurnal tidal displacements of the surface always exceed diurnal tidal displacements along the coast in the Arctic Ocean. Currents were recorded with meters suspended below two drifting ice stations, FRAM III in 1981 and FRAM IV in 1982, as they traveled over several weeks from a region of abyssal depths onto the western flank of the Yermak Plateau. Ice drift velocity was calculated from satellite positions and then vectorially added to the recorded data to produce current velocity relative to the bottom. Diurnal tidal currents with spectral peaks greater than semidiurnal peaks were observed in both years with current speeds reaching 30 cm/s over the edge of the Plateau. Semidiurnal tidal currents over the middle and lower slope were principally alongslope which is consistent with Kelvin wave motion. Diurnal tidal currents on the middle and lower slope were across-slope, and on the upper slope they had a clockwise rotary motion suggestive of topographic vorticity waves. These unusually large diurnal tides are apparently vorticity waves which have been resonantly forced by weak deep-sea diurnal tides. (Author)