Baseline study of ocean dynamics in support of Repsol exploration driling project off the south coast of Portugal, May-July 2014

Abstract

Current observations covering the whole water column at the transition from the Diogo Cão Trench to the Bartolomeu Dias Plateau, off the south coast of Portugal, revealed one-month vector averaged current of 25-30 cm/s in the lower 250 m of the water column, with indications of a possible anticlokwise circulation over the plateau. Oscillations at the local inertial frequency appeared ubiquitous in both the surface layer and in the depth layers above the bottom 250 m, overriding the tidal currents. These clockwise polarized current oscillations had amplitudes of the order of 10 cm/s and added to low-frequency oscillations with similar amplitudes, determining maximum speeds in excess of 20 cm/s. A sustained flow along the bottom, with only occasional current drops, promoted and maintained a sediment suspension along most of the observation, in such a way that near-bottom echo intensity increased significantly when the current dropped