Pelagic primary production in the Algero-Provençal basin by means of multisensor satellite data: focus on interannual variability and its drivers

In this work, we make use of satellite esti-mates of chlorophylla, photosynthetically active radia-tion and sea surface temperatures, to compute regionalestimates of primary production integrated throughoutthe euphotic layer for the Algero-Provençal Basin, bymeans of a modified version of the vertically general-ized production model. The seasonal and interannualvariability of the primary production has been analysedover the decade 1997-2007. Empirical orthogonal func-tions analysis has been applied to decompose the vari-ability of the primary production dataset in orthogonalmodes of variability. The seasonal signal is distributedbetween the two first modes of variability, temporallyshifted each other and respectively related to the north-ern (early spring) and the southern (winter) part of thebasin. We found a minimum of the annual productionin 2003, when a summer heatwave strongly enhancedthe stratification of surface waters, further limiting theinjection of nutrients into the surface layers. Maximain the annual series are found in 1999 and 2005, dueto two particularly intense and extended (in space)spring-blooms in the northern part of the basin. Thesetwo maxima, clearly identified in space and time byEOF analysis (EOF1 and EOF3), are related to strongmistral-wind interannual events occurring during win-ters of 1999 and 2005, preceding the blooms by someResponsible Editor: Joachim W DippnerA. Olita (B)·R. Sorgente·A. Ribotti·L. Fazioli·A. PerilliNational Research Council,Institute for Coastal Marine Environment,Loc. Sa Mardini, 09170 Torre Grande, Oristano Italye-mail: antonio.olita@iamc.cnr.itfew months. We found that these production maximaare due both to a more intense production in the usualblooming area (shown by EOF1-PC1) as well as to anexceptional local production in the eastern side of thebasin, off the Corsica western coasts (EOF3-PC3). Pre-vious observations of exceptional deep-water forma-tion events in 1999 and 2005, with easterly spots closeto the primary production-observed anomalies, and themeridional character of the mistral 1999 and 2005 peaksboth support the idea that such eastern PP interannualmaxima would be actually due to exceptional produc-tion more than to an easterly advection of biomass fromthe usual bloom area. Finally, the potential link of theobserved features with large-scale atmospheric forcingis discussed, and a potential relation of such interannualevents with the East Atlantic pattern is drawn.