Variabilité interannuelle d'un indice d'intensité des remontées d'eau dans le secteur du cap Blanc (Mauritanie)

The coastal waters along the Atlantic Sahara are characterized by intense hydrodynamic phenomena (upwellings, water mass alternations) throughout the year that deeply influence their productivity. Deep-water arrivals at surface levels are closely related to the local prevailing winds dominating all year long, the Northeast Trade winds. Working on a time series of 28 yr shows that far from being regular and constant during that period, the Trade winds were very variable. The coastal upwellings induced by these winds showed important intensity variations: after years of strong activity (1955–60) there was a period of minimal activity (1961–69), which was followed by a period of great irregularity (1970–82), showing a progressive return to the initial conditions. These important variations inducing deep hydrological consequences and modifications of water trophic potentialities can be related to the biological anomalies observed during the same time in the Northwest Africa fisheries.