Low-frequency variability of the Mediterranean undercurrent off Galicia, northwestern Iberian Peninsula

Abstract The variability of the Mediterranean flow off Galicia, at the northwestern corner of the Iberian Peninsula has been investigated by means of a four-month time series of velocity and temperature collected at two different sites in the depth range of the Mediterranean water influence. The time series cover the initial and development phases of the seasonal upwelling and indicate that the vein of Mediterranean water is raised and, probably, displaced shoreward as the upwelling sets up. Data show that the vein flows around 100 m shallower in September, when the seasonal upwelling is developed the most, than in May, before the upwelling season starts. The raising is not achieved in a smooth and continuous manner but undergoing noticeable mesoscale variability that has been assigned to vertical and horizontal (inshore–offshore) displacements of the vein, whose origin is partially related to the variability of the large-scale wind field. The footprint that the internal tide leaves in the temperature records at M2 tidal frequency in the instruments placed above and below the core of the Mediterranean vein along with the registered temperature have been used to diagnose the subtidal displacements of the vein.