Deep-Sea Research II 49 (2002) 4115–4130 Physical–biological coupling in the Strait of Gibraltar Fidel Echevarr ! ıa a, *, Jes ! us Garc ! ıa Lafuente b , Miguel Bruno c , Gabriel Gorsky d , Madeleine Goutx e , Nicol ! as Gonz ! alez f , Carlos M. Garc ! ıa a , Fernando G ! omez a , Juan M. Vargas b , Marc Picheral d , Laurent Striby e , Manuel Varela f , Jose J. Alonso c , Andreas Reul g , Andr ! es C ! ozar a , Laura Prieto a , Tarek Sarhan b , Francisco Plaza b , Francisco Jim! enez-G ! omez h a Area de Ecolog ! ıa, Facultad de Ciencias del Mar, Universidad de C ! adiz, 11510 Puerto Real, C ! adiz, Spain b Departamento de F! ısica Aplicada II. Universidad de M ! alaga. Campus de Teatinos. 29071 M ! alaga, Spain c Departamento de F! ısica Aplicada, Facultad de Ciencias del Mar, Universidad de C ! adiz, 11510 Puerto Real, C ! adiz, Spain d Laboratoire d’Oceanographie Biologique et Ecologie du Plancton Marin, Station Zoologique, 06234 Villefranche sur Mer, France e Laboratoire de Microbiologie Marine, CNRS/INSU-EP2032, Universite de la Mediterranee, Campus de Luminy, Case 907, Marseille Cedex 9, France f Instituto Espa * nol de Oceanograf ! ıa, Muelle de Animas s/n, 15001 A Coru * na, Spain g Departamento de Ecolog ! ıa. Universidad de M ! alaga. Campus de Teatinos. 29071 Malaga, Spain h Departamento de Biolog ! ıa Animal, Vegetal y Ecolog ! ıa. Universidad de Jaen. Paraje Las Lagunillas s/n. 23071 Jaen, Spain Received 28 April 2000; received in revised form 28 March 2001; accepted 17 July 2001 Abstract This study presents a joint analysis of the distributions of some biogeochemical variables and their relation to the hydrodynamics of Gibraltar Strait. It is a synthesis paper that brings together many results obtained during CANIGO project. We show the role of hydrodynamics as a forcing agent for the plankton community structure in the Strait, with emphasis on the two physical processes that we propose as key factors for the coupling: interface position and oscillations, and mixing processes along the Strait. As a general pattern, autotrophic plankton biomass increases at the Strait from southwest to northeast, a tendency that coincides with a gradual elevation of the interface depth in the same direction. The different mechanisms of mixing that take place in the Strait are briefly reviewed: The occurrence of the internal hydraulic jump is an important mechanism of mixing constrained to the spring tide situations, but other processes such as the generation of arrested internal waves of wavelength around 1 km are proposed as a complementary mixing mechanism, particularly during neap tides situations. Both mechanisms, the elevation of the pycnocline and these mixing events, can enhance biological productivity and biomass accumulation on the northeastern sector of the Strait, since phytoplankton cells are there packaged in a water mass with sufficient light and nutrients and smaller advective velocity. There is a clear north–south difference in the biological response to these upwelling episodes in the eastern section, with high nutrient and low chlorophyll in the south and the opposite in the north. The deeper interface and the greater water speed are the proposed reasons for this lower nutrient uptake on the southeastern sector. Finally, the temporal scales of variation of the mixing events, the influence of its periodicity on the productivity of the area and the influence of these upwelling episodes in the nearest Albor ! an Sea are discussed. r 2002 Elsevier Science Ltd. All rights reserved. *Corresponding author. Tel.: +34-956-01-6025; fax: +34-956-01-6019. E-mail address: fidel.echevarria@uca.es (F. Echevarr ! ıa). 0967-0645/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII:S0967-0645(02)00145-5