Variability of the large scale general circulation of the Mediterranean Sea from observations and modelling: a review

In this paper we present an overview of the most recent findings about the Mediterranean Sea present-day circulation structure. Both historical observations and numerical model simulations are presented, outlining the differences and agreement. The model simulations are presented for both an eddy resolving and a coarse resolution numerical model and the results are intercompared. The importance of the mesoscales in modifying the large scale flow field is elucidated. The critical point is the discovery of the large amplitude interannual variability of the circulation and water mass structure associated with the anomalies of atmospheric forcing over the basin. The seasonal variability can be strictly related to changes in heat and momentum fluxes, while the interannual variability has a component which is related to the mesoscale field. The latter is very intense in the Algerian Current region and Levantine basin but different in structure in the two regions. Results are shown, which confirm the importance of wind driving in establishing the kinetic energy of the flow field, by comparing the current transport at the Strait of Corsica with observations. In conclusion, the essential characteristics of the present-day circulation are associated with the atmospheric forcing and the basin topographic structure. Results from palaeoceanographic simulations for the last 20 000 years show that changing the atmospheric forcing can cause large changes in circulation structure which may have affected sapropel formation. (C) 2000 Elsevier Science B.V. All rights reserved.