Comparison between sea surface features from ocean color imagery and 3D modeling in the gulf of lions (Northern Mediterranean sea)

The signature of the Gulf of Lions (GoL) surface dynamics by SeaWiFS measurements of chlorophyll (Chl) is addressed in this paper. A chain of three nested models based on the MARS-3D code is used to simulate the Northwestern Mediterranean Sea circulation. This modeling network allows to resolve the Gulf of Lions (GoL) dynamics taking into account the influence of the general basin circulation (Northern Current). A good qualitative agreement between Chl and modeled salinity fields was generally obtained. From SeaWiFS images and according to the model results, the Rhone water masses can follow the coasts to the west of the river mouth or can be expelled southward in the western part of the GoL. Along the continental slope, the Northern Current (NC) channels the Rhone river dispersion plume up to the Catalan coasts. In bloom condition the localization of the oligotrophic vein corresponds accurately to the NC position. Small scale dynamics observed on chlorophyll fields are generally reproduced by the model. However they can be misplaced on MARS-3D results because of the difficulties to simulate these small scale processes and the too coarse resolution of wind forcing. Finally, the quantitative pixel/pixel comparisons between the Chl fields and the computed surface salinity fields show a high scattering due to the misplacement of features. Nevertheless, two clear trends was observed, corresponding to the southwestward and the along coast direction of the Rhone river plume.