Coupling between the thermohaline, chemical and biological fields during two contrasting upwelling events off the NW Iberian Peninsula

Abstract

The hydrographic, chemical and biological conditions observed during spring and summer upwelling events off the NW Iberian Peninsula are compared. Meteorological data showed that northeasterly winds were of similar magnitude during both cruises, whereas the effect of upwelling was more intense during the spring than during the summer since stratification was weaker in spring. In the two situations the recurrent upwelling centre off Cape Finisterre (43°N, 9°W) divided the study area into two provinces. The two provinces differ in the occurrence and intensity of winds and in the origin of the upwelled water. Eastern North Atlantic Central Water of subpolar origin (ENACW P) was recorded north of Cape Finisterre during the two events. South of the Cape, ENACW P was observed during the spring situation, whereas ENACW of subtropical origin (ENACW T) prevailed during the summer cruise. Despite the different thermohaline and chemical properties of these two varieties of ENACW, similar nutrient levels were found in the two provinces due to strong remineralisation processes on the southern shelf. In addition, slower horizontal circulation at the southern edge of the upwelling centre and the influence of four large embayments (the Rı́as Baixas) south of Cape Finisterre, favoured chlorophyll accumulation south of the upwelling centre, which has similarly been observed in other upwelling centres around the world.