Island-generated internal waves at Scott Reef, Western Australia

Abstract

Oceanographic field studies were carried out, in August–October 1993, of the water circulation around Scott Reef, a 39 km wide island rising nearly vertically in 500 m depth on the outer continental shelf slope of Western Australia. Macro-tide prevailed and generated 0.6 m s -1 tidal currents. Internal waves 60 m peak-to-trough occurred around Scott Reef mainly at the semi-diurnal frequencies. A numerical model and the field data suggested that the internal waves were locally generated by the interaction of the tidal currents and the bathymetry. Also these waves were predicted to rotate counterclockwise around the island with maximum amplitude along the island slopes, while radiating energy as free internal waves propagating freely away in the open ocean. They were generated apparently without eddies forming in the lee of the island. The wave frequencies were not restricted to the diurnal and semi-diurnal tidal frequencies which dominated the sea surface fluctuations, indeed higher frequencies were important. The energy at the inertial frequency was negligible. It appears that oceanic islands are internal wave generators and may contribute to the oceanic variability even far away.