On the vertical distribution of the chlorophyll ia/i concentration in the Mediterranean Sea: a basin-scale and seasonal approach

摘要

The distribution of the chlorophyll a concentration ([Chl a]) in theMediterranean Sea, mainly obtained from satellite surface observations orfrom scattered in situ experiments, is updated by analyzing a database offluorescence profiles converted into [Chl a]. The database, which includes6790 fluorescence profiles from various origins, was processed with aspecific quality control procedure. To ensure homogeneity between thedifferent data sources, 65 % of fluorescence profiles have beenintercalibrated on the basis of their concomitant satellite [Chl a]estimation. The climatological pattern of [Chl a] vertical profiles in fourkey sites of the Mediterranean Sea has been analyzed. Climatological resultsconfirm previous findings over the range of existing [Chl a] values andthroughout the principal Mediterranean trophic regimes. They also provide newinsights into the seasonal variability in the shape of the vertical [Chl a]profile, inaccessible through remote-sensing observations. An analysis based onthe recognition of the general shape of the fluorescence profile was alsoperformed. Although the shape of [Chl a] vertical distributioncharacterized by a deep chlorophyll maximum (DCM) is ubiquitous duringsummer, different forms are observed during winter, thus suggesting thatfactors affecting the vertical distribution of the biomass are complex andhighly variable. The [Chl a] spatial distribution in the Mediterranean Seamimics, on smaller scales, what is observed in the global ocean. As alreadyevidenced by analyzing satellite surface observations, midlatitude- andsubtropical-like phytoplankton dynamics coexist in the Mediterranean Sea.Moreover, the Mediterranean DCM variability appears to be characterized bypatterns already observed on the global scale.