A high-salinity poleward-flowing compensation undercurrent, carrying subtropical Eastern North Atlantic Central Water (ENACW1), is recurrently observed off NW Spain during the "upwelling season" (April to September). The poleward flow surfaces during the transition from upwelling-favourable northeriy winds to downwelling-favourable southerly winds by September-October. The poleward transport of ENACW1 in the upper ocean produces unexpectedly warm and salty waters off NW Spain during the autwnn and winter compared to the surrounding subpolar waters of the NE Atlantic. NO3 -, HPO4- and Si(OH)4 levels in ENACWT -fipm south of 40°N. the latitude of Cape Mondego, Portugal- are much lower than in subpolar ENACW (ENACWr)-from north of 43°N, the latitude of Cape Finisterre. Spain. Contrasting nutrient status affect the microplankton community structure and the distributions of the reduced forms ofN-nutrients (NO2- and NH4-). Seasonal changes in the thermohaline, chemical and biological setting of the poleward flowing slope current are studied in response to the decreasing stratification from the middle summer to the middle winter. Data collected during cruises Be9815c (June 27- July 7, 1998; OMEX-II. MAST-III). Galicia XII (September 1991, MAST-I), MORENA II (December 1993. MORENA. MAST-II) and CD110b (10-16 January 1998, OMEX-11, MAST-III)

Poster.-- 32nd International Liege Colloquium on Ocean Hydrodynamics Exchange Processes at the Oceans Margins, Liège, Belgium, May 8-12 2000

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