A seasonal three-dimensional study of the nitrogen cycle in the Mediterranean Sea - Part I. Model implementation and numerical results

The influence of the general circulation on the lower trophic level variabi lity in the Mediterranean is investigated by means of a three-dimensional c oupled hydrodynamical ecological model. While the hydrodynamical forcing is obtained by a primitive equation seasonal model, the trophic dynamics are described using an aggregated model based on inorganic nitrogen, phytoplank ton and detritus. The model results exhibit a quasi-repeating seasonal cycl e and the calculated fluxes through the principal straits are of the same o rder as those estimated from literature data. The climatological influence of the general circulation on the nutrient distribution is evident in perma nent cyclonic areas, while the anticyclonic circulation does not give a det ectable signal, due to the high oligotrophy of the upper layer. The seasona l cycle shows marked spatial differences according to the different regimes induced by the surface circulation, leading to the tentative conclusion th at, in the upper layer, the circulation directly or indirectly determines t he distribution of the dissolved inorganic nitrogen concentration. (C) 1998 Elsevier Science B.V. All rights reserved.