Spatio-temporal variability of the winter phytoplankton distribution across the Catalan and North Balearic fronts (NW Mediterranean)

The qualitative and quantitative composition of the phytoplanktonassemblages of the Catalano-Balearic Sea (NW Mediterranean) was examined inrelationship with frontal boundaries and short-term meteorological forcingoriginated by an intense wind storm. Data were obtained during February1990, before and after strong NW winds, from several transects across theCatalan (continental side) and North Balearic (Balearic Islands side)shelf/slope fronts. High chlorophyll concentrations and diatom dominanceinshore of the Catalan Front were typical of the winter-springphytoplankton maximum. However, offshore of the Catalan Front, diatoms werescarce and the phytoplankton assemblage was dominated by coccolithophorids.In spite of weak density stratification, a deep chlorophyll maximum (DCM)was well developed, before the storm, offshore and appeared to cause apulse of new production, as suggested by increased oxygen concentrations inthe vicinity of the DCM. The results presented here indicate the existenceof a persistent association between the distribution of distinctphytoplankton assemblages and hydrographic characteristics of the studiedarea. Our results also show that, at least during an important part of thewinter-spring bloom period of the Catalano-Balearic Sea, high phytoplanktonbiomass offshore of the Catalan Front is not associated with the diatomdominance typically found in coastal waters and other offshore areas of theNW Mediterranean. This finding has biogeochemical implications inrelationship with vertical export fluxes of particulate matter.