Baseline study of ocean dynamics in support of Repsol exploration driling project off the south coast of Portugal, April-May 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 maximum detided current speeds of 40 cm/s in the lower 400 m of the water column. The current in two moorings showed significant topographic steering, being consistently towards W to WNW, in a suggestion of a possible anticlockwise circulation over the plateau. Current pulses were associated with temperature rises, as expected in an area whose dynamics is controlled by the Mediterranean Water. Significant sediment re-suspension was revealed by the echo intensity in the 120-140 m closed to the bottom. Tidal currents were only dominant in the upper part of the water column, particularly in the 20 m closest to the surface, where speeds of the 10-30 cm/s were observed and tidal harmonics could be identified. Below the surface layer, current oscillations at the local inertial frequency were recurrent throughout the water column, dominating the daily band