Abyssal Penetration and Bottom Reflection of Internal Tidal Energy in the Bay of Biscay

Abstract

This paper describes field observations in the Bay of Biscay, and presents convincing evidence for the existence of a broad beam of internal tidal energy propagating downward from a source region on the upper continental slopes, which, after penetrating the deep ocean interior along a theoretical ray path, reaches the abyssal plain, at a depth of about 4.2 km, 58 km from the source. The results concentrate on the region between 50 and 60 km from the generating area, where the beam of energy is below a depth of 2 km. A marked change in phase of the beam (4 hours) was observed over a distance of 12 km at a depth of about 3 km. In addition, semidiurnal currents were noticeably increased near the sea floor. These results are interpreted as demonstrating the occurrence of partial bottom reflection of the internal tidal energy, in agreement with theoretical predictions, at a distance of about 58 km from the generating region on the upper slope, and extend our previous results farther into the ocean.