Coastal circualtion over the Gulf of Cadiz continental shelf. Local vs remote effects.

Resumen

Studies about the coastal circulation over the northern continental shelf of the Gulf of Cadiz, based on current velocity observations, were published on relatively recent dates (e.g., Relvas and Barton, 2002). Since then, a considerable number of articles have been written dealing with this subject up to the present date (e.g., Oliveira et al., 2022). One of the most studied features in these studies are the so-called Coastal Counter Currents (CCCs) in the coastal shelf. These features are located roughly between the 100 m isobath and the coastline, and they are directed toward west. Nevertheless, despite the considerable number of articles devoted to the analysis of this phenomenon, the actual along-coast extension and origin of these CCCs remain unclear.In the present contribution different mechanisms that have been already proposed to explain the development of these CCCs are revised and discussed. For this purpose, an analysis based on surface currents derived from High Frequency Radar (HFR) and numerical model simulations has been carried out. The most interesting finding is that the most intense CCCs events are initiated on the coastal margin of the westernmost side of the Strait of Gibraltar, and they are extended further west of Cape Santa Maria. Also, these intense and extensive CCCs are triggered by the joint action of local winds over the Gulf of Cadiz and additional remote effects. This study highlights the importance of different remote effects: (i) the wind forcing over the Alboran Sea and the easternmost side of the Strait of Gibraltar, and (ii) the sea level atmospheric pressure forcing over the Ligurian Sea. This mechanism has been demonstrated from both statistical analysis and numerical experiments which allow us to understand the coupling between the horizontal and transverse pressure gradients, causing a geostrophic adjustment of the current against the coast.