Upwelling mechanisms in the northwestern Alboran Sea

From April 1996 to July 1997, a series of hydrographic surveys were carried out in the Northwestern part of the Alboran Sea to investigate the upwelli ng that is an almost permanent feature in this area. Simultaneously a moori ng line was deployed in the north part of the eastern section of the Strait of Gibraltar to monitor the variability of the Atlantic Jet (AJ). Two mech anisms are shown to be relevant for the upwelling dynamic in the region: th e southward drifting of the Al and wind stress. A linear relation between t he angle under which the Jet enters the Alboran Sea and the distance from t he coastline to the front associated with the Jet has been found. This angl e that has been estimated from the low passed time series of current veloci ty measured by the uppermost instrument of the moored line has been then us ed to identify the onshore-offshore excursions of the Jet. Both upwelling m echanisms are identified from hydrographic data, because each of them has a ssociated a different type of water mass, and they take place:in different locations. Wind-driven upwelling dominates in coastal zones, on the shelf, while upwelling associated with southward drifting of the Al prevails furth er offshore, The amount of sub-surface water brought up to the surface by e ach one is of the same order. However, wind-driven upwelling contributes to the fertilization of this region in a major extent because water upwelled by wind is richer in nutrient concentration. (C) 2000 Elsevier Science B.V. All rights reserved.