Tidal currents at two deep-sea moorings near the shelf edge

Abstract

The currents measured at two deep-sea moorings near the northwest European continental shelf edge were investigated for evidence of internal tides. One mooring, Sta. Z1, in the Rockall Trough near Porcupine Bank, showed no such evidence. The other, Sta. I, off the Celtic Sea shelf edge, showed clear evidence of a strong first mode baroclinic M 2 tide, with surface currents greater than those of the barotropic tide. The second baroclinic mode was also significant. No such baroclinic modes could be found for the S 2 tide, probably because the signal-to-noise ratio was too low. The energy flux in the first baroclinic mode was estimated to be 1.8 kW m −1, but the direction was uncertain. At both sites 29-day means suggest a barotropic, topographically steered poleward flow of about 5 cm s −1 along the shelf edge.