An upwelling filament off southwest Iberia: Effect on the chlorophyll a and nutrient export Alexandra Cravo a,n , Paulo Relvas a,1 , Sara Cardeira a , Filomena Rita a , Miguel Madureira a , Ricardo Sa ´ nchez b a CIMA, FCT, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal b Centro Oceanogra ´fico de Ca ´diz, Muelle de Levante s/n, P.O. Box 2609, E-11006 Ca ´diz, Spain article info Article history: Received 1 September 2009 Received in revised form 27 April 2010 Accepted 10 June 2010 Available online 22 June 2010 Keywords: Iberian peninsula Upwelling Filaments Nutrients Chlorophyll a Dissolved oxygen abstract The present paper describes the chemical and biological characteristics of an upwelling filament off southern Iberia in October 2004, based on a total of 42 CTD casts, along with ADCP velocity measurements distributed by an almost regular grid of 15 km mean spacing. Stations were sampled from the surface to a maximum depth of 400 dbar, for nutrients (nitrate, phosphate and silicate) and chlorophyll a determination. The effect of cross-shelf exchange of nutrients and chlorophyll a between the coastal and oceanic waters was also investigated. Data revealed that, during the cruise conducted under relaxed winds, a relatively small filament was formed down to 75 m. However, an amount of 180 t of chlorophyll a was estimated there accompanied by low nutrient concentrations. The observed water properties reveal that SW Iberia is similar to NW Iberia, showing the continuity of the Canary Upwelling System along the Iberian Peninsula, one of poorest upwelling systems of the oceanic eastern boundaries. Nevertheless, the amounts of chlorophyll and nutrients transported through the filament are significant, revealing that those play a key role in the seaward export of matter with an important impact on the regional oceanography of this region. Considering the periods of strong upwelling events and the extent of their duration along the year, the amounts of exported matter must be hugely increased and responsible for the high productivity of these waters. & 2010 Elsevier Ltd. All rights reserved. 1. Introduction Filaments of cold subsurface water, upwelled in the coastal regions under favourable winds, are recognized as efficient contributors for the exchange processes between the coastal productive waters and the open ocean oligotrophic waters (Levı ´, 2008). At the eastern boundary regions, filaments have shown to play a key role in the transport of nutrients and chlorophyll a to the open ocean (Jones et al., 1991; Basterretxea and Aristegui, 2000; A ´ lvarez-Salgado et al., 2001, 2007). Horizontal offshore mass transport is favoured at sites where large upwelling filaments develop (e.g. Brink and Cowles, 1991; Barton, 1998; A ´ lvarez-Salgado et al., 2001). In the NE Atlantic it has been suggested that a large fraction of primary production generated in the eutrophic coastal upwelling regions could be advected into the waters of the open oceans (A ´ lvarez-Salgado et al., 2001, 2007; Garcia-Mun ˜oz et al., 2004). However limited knowledge of the dynamics and variability of upwelling filaments makes it difficult to draw any global conclusions on their biological effects. Such structures develop seaward from the contorted upwelling front reaching up to 250 km of length and about 50 km width and leave a clear signature in sea surface temperature satellite imagery. Filaments are upper layer structures, barely exceeding the top 150 m. Offshore velocities inside the filament jet are surface intensified reaching almost 1 m s 1 (e.g. Kosro et al., 1991). A weaker return flow accompanies the filament in the downstream side. Filaments can persist even during periods when there are no upwelling favourable winds, meaning that these structures have greater inertia than the costal upwelling itself (Pelegrı ´ et al., 2005). This represents a continuous source of matter to the open ocean. Western Iberia is part of the Canary Current System that forms the Eastern Boundary Upwelling System of the N. Atlantic. The culminating point of SW Iberia, the Cape S ~ ao Vicente (Fig. 1), is the root of a recurrent well developed filament observed in satellite imagery during the upwelling season (Haynes et al., 1993), defined as April–October for the western Iberia (Wooster et al., 1976). This filament was sampled in October 2004, during the final stages of the upwelling season. Nevertheless, the physical description of the filament carried out by Sa ´ nchez et al. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/csr Continental Shelf Research 0278-4343/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.csr.2010.06.007 n Correspondence to: CIMA, FCT, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal. Tel.: + 351 289 800 900; fax: + 351 289 800 069. E-mail address: acravo@ualg.pt (A. Cravo). 1 Present address: CCMAR, University of Algarve; Campus de Gambelas, 8005-139 Faro, Portugal. Continental Shelf Research 30 (2010) 1601–1613