The effects of a winter upwelling on biogeochemical and planktonic components in an area close to the Galician Upwelling Core: The Sound of Corcubión (NW Spain)

To study the biogeochemical response and the coupling plankton–benthos to an unusual winter upwelling event a cruise was carried out in February 2005 in the Sound of Corcubión, near Cape Finisterre (NW Iberian Peninsula), the Galician upwelling core. This area represents the northern boundary of the Eastern North Atlantic Upwelling System (ENAUS). The spatial distribution of plankton assemblages (phytoplankton and zooplankton), chlorophyll, physical and chemical parameters as well as diatom distribution in surface sediments, were studied in a total of 17 stations in the Sound. The upwelling processes caused an important accumulation of water in the inner Sound and near the Cape. This accumulation zone must be persistent through the upwelling events in the area, including those of summer, as indicated by the diatoms' distribution in the sediment. Unlike the summer upwelling events, the main effect of winter upwelling in the area is the increase in solar radiation due to the persistent clear skies. In this season nutrient supply is not critical due to water column mixing. The meteorological conditions were equivalent to those of early spring. As a result, both phyto- and zooplankton species assemblages were typical of spring blooms in Galician coasts. The bloom lasted for up to 6 days, as estimated from the availability and uptake of nitrogen forms. Winter blooms represented ca. 20% of total annual phytoplankton biomass, and 30% of the average biomass during summer upwelling, in the period 1997–2007, as estimated from the analysis of both, in situ and satellite derived chlorophyll.