Modelling the Mediterranean pelagic ecosystem using the POSEIDON ecological model. Part I: Nutrients and chlorophyll-a dynamics

Ecosystem models are recognized as valuable tools to understand marine ecosystem dynamics and address management questions, requiring an integrated approach of physical and biotic processes. In the present study, a three-dimensional basin scale Mediterranean hydrodynamic/biogeochemical model, currently operational as part of the POSEIDON forecasting system, was extensively validated against available in-situ and satellite data. The generic POSEIDON ecosystem model skill was objectively assessed, in capturing the observed seasonal variability of the main chemical ecosystem components within the planktonic food web. A cluster K-means analysis was applied to obtain an objective `biogeography' of the Mediterranean Sea, allowing a more efficient validation of model outputs against observational data. The model presented a reasonable skill in reproducing the seasonal cycle and observed patterns of the Mediterranean inorganic nutrients and chlorophyll-a, characterized by a prominent west-to-east gradient and their increase in areas receiving lateral nutrient inputs. Despite some model deviations, validation results have demonstrated the capability of the model to represent the Mediterranean ecosystem, ranging from oligotrophic open ocean to mesotrophic conditions in productive coastal areas.