Ocean margin exchange — water f lux estimates John M. Huthnance a, * , Hendrik M. Van Aken b , Martin White c , E. Desmond Barton d , Bernard Le Cann e , Emanuel Ferreira Coelho f , Enrique Alvarez Fanjul g , Peter Miller h , Joao Vitorino f a Proudman Oceanographic Laboratory, Bidston Observatory, Birkenhead, Merseyside CH43 7RA, UK b Nederlands Instituut voor Onderzoek der Zee, P.O. Box 59, 1790 AB Den Burg, Texel, Netherlands c Department of Oceanography, NUI Galway, University Road, Galway, Ireland d School of Ocean Sciences, University of Wales—Bangor, Menai Bridge, Gwynedd LL59 5EY, UK e Laboratoire de Physique des Oceans, UFR Sciences 6, avenue Le Gorgeu, BP 809 29285 Brest Cedex, France f Marinha-Instituto Hidrografico, Rua das Trinas, 49, P-1249-093 Lisbon, Portugal g Puertos del Estado, Avenida del Parteno ´n 10, 28042 Madrid, Spain h Plymouth Marine Laboratory, Prospect Place, West Hoe, Plymouth PL1 3DH, UK Received 27 October 2000; accepted 23 June 2001 Abstract Hydrographic data define source regions for deep, intermediate and upper-ocean water types found near the northwest Iberian margin; these water masses’ structure and geostrophic flow are described. Labrador Sea Water (LSW) moves south through the region; above this at 1000 m, particularly near the coast, Mediterranean Sea Outflow Water (MSOW) moves north. Near-surface waters are more seasonal, and we distinguish summer and winter regimes. Summer: above 600 m, poleward flow over the slope is at a minimum in spring and summer, and a maximum in the autumn/early winter. Overlying this is a general southward flow linked to wind stress. Summer upwelling along the Iberian shelf has associated offshore filaments stretching westward, and appears most intense around Finisterre (starting earlier, more persistent). The vertical upwelling flux is s/qf but lateral exchange in filaments may be more. Winter: it is proposed that upper layers of the water column offshore are fed from the north. Potential vorticity calculations suggest enhanced diapycnic mixing. However, other data indicate an east– west front down to about 300 m at 39–40jN, i.e., north –south convergence. This front bends to the north near the shelf edge, in accord with a warm flow along the upper slope, 0.15 m/s or more. Surface temperatures often show a much broader (hundreds of kilometers) northward extension of warm water, probably affected by winds. The thermocline from the previous summer can persist to January at least. Coastal waters show cooler river runoff. Budgeting of water fluxes is discussed in relation to direct estimates (from water mass properties and current measurements) and in relation to possible process contributions to fluxes. On/ off-shelf exchange has a relatively short time scale, estimated at about 12 days. Upwelling (mostly) and mixing may supply the nutrient content of about 200 m water depth for new production over the shelf. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Water masses; Currents; Dispersion; Water mixing; Shelf edge; Exchange; ANE (NE Atlantic); Iberia; Galicia 1. Introduction Ocean margin fluxes between productive shelf seas and nutrient-rich oceanic waters are important to 0924-7963/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0924-7963(02)00034-9 * Corresponding author. Tel.: +44-151-653-8633; fax: +44-151- 653-6269. E-mail address: jmh@pol.ac.uk (J.M. Huthnance). www.elsevier.com/locate/jmarsys Journal of Marine Systems 32 (2002) 107 – 137