SPACE AND SEASONAL DISTRIBUTIONS OF NITRATES IN THE MEDITERRANEAN-SEADERIVED FROM A VARIATIONAL INVERSE MODEL

A variational inverse model was applied to the processing of biogeoche mical data in order to generate conceptual models useful for understan ding the role of anthropogenic and physical factors in eutrophication and other environmental characteristics of the Mediterranean Sea. For this purpose, nitrate concentrations available in our data base were g rouped into synoptic or quasi-synoptic subsets representative of avera ged values of the measured vertical profiles in typical water layers. These data sets were then used as input for our two-dimensional variat ional inverse model based on a minimum principle to reconstruct mean h orizontal distributions of the nitrate data fields. The latter are obt ained as gridded solutions to the measured concentrations. The resulti ng seasonal distributions of nitrates provide an interesting general v iew, and indicate gaps where new data must be supplemented for further investigations. In some coastal regions where data are available, kno wn phenomena such as nutrient loadings from rivers, upwelling regions and gyres were reproduced by this model in both the western and easter n Mediterranean basins. Seasonal graphical visualisations of the varia tional inverse model results are presented for nitrate concentrations. Besides providing a new insight into the distribution of nitrates in the Mediterranean Sea, our results confirm the need for more up-to-dat e and good quality data before any definite conclusion concerning long -term seasonal modelling and the fate of nutrients can be drawn. (C) 1 998 Elsevier Science Ltd. All rights reserved.