Seasonal to interannual phytoplankton response to physical processes in the Mediterranean Sea from satellite observations

The relation between physical and biological processes affecting the Mediterranean Sea surface layer was investigated through univariate Empirical Orthogonal Function (EOF) decompositions of remotely sensed chlorophyll-a (CHL), sea surface temperature (SST) and Mediterranean Absolute Dynamic Topography (MADT) weekly time series (1998–2006). As part of the analysis, the Data INterpolating Empirical Orthogonal Functions (DINEOF) technique was successfully applied to CHL images. Results from the single EOFs, along with a cross-correlation analysis, identified physical–biological interactions at both short (weeks to months) and long (years) temporal scales, and from meso- to basin-scales. Phytoplankton biomass abundance and the sea surface thermal stratification show a strong inverse relationship at seasonal and sub-basin scales. At a regional scale, the spring bloom space–time variability is related to the intensity and spatial extent of the deep water formation process and especially to its pre-conditioning phase. At interannual and sub-basin scales, a gradual decline of the phytoplankton biomass in the whole central Mediterranean occurs with a delay of one year relative to the decrease of the cyclonic circulation in the eastern basin, and the northward displacement of the Algerian current. Regionally, the phytoplankton biomass and the surface heat content anomalies associated with extreme atmospheric anomalies (such as the cold 1998–1999 winter and the summer 2003 heat wave) show a significant correlation with a ~ 5-month time lag.