VARIABILITY OF DEEP CHLOROPHYLL MAXIMUM CHARACTERISTICS IN THE NORTHWESTERN MEDITERRANEAN

A well-developed deep chlorophyll maximum (DCM) is a prominent feature of the Northwestern Mediterranean during a large part of the year. Data from 7 oceanographic surveys carried out across the Catalano-Balearic Sea, between 1982 and 1987, have been used to analyze short-term (within cruises) and seasonal+interannual (between cruises) variation of several parameters (such as surface and DCM chlorophyll concentration, integrated chlorophyll, DCM, nitracline and nitrite maximum depths). Significant positive correlations (p < 0.01) were found between the depths of the DCM, of the nitracline and of the nitrite maximum. Surface chlorophyll concentrations and average chlorophyll values for the upper 1 10 m of the water column were signicantly correlated for only 2 of the 7 cruises. The relationship between integrated primary production and surface or integrated chlorophyll concentrations presented considerable scatter due, in part, to physiological variability of the sampled communities. After exclusion of 1 statistically outlying point, apparently corresponding to a sedimenting bloom, a multiple linear regression model of integrated primary production (mg C m-2 h-1) on integrated chlorophyll, euphotic zone depth and a stability parameter explained 74 % of the data variance. However, the presence of such 'outliers' limits the usefulness of these models and stresses the need of physiological information for a reliable prediction of primary productivity.