The Ligurian Sea and the surrounding Gulf of Lyon of the Liguro-Provencal basin are among the most dynamic and productive areas within the whole Mediterranean Sea. It is a deep, semi-enclosed sea with a narrow continental shelf surrounded by the Alps to the North and by the Corsica Island to the South. The basin exchanges water with the southern part of the Western Mediterranean trough the Corsica channel alongside the Italian coast.
The Ligurian Sea is the more inland sea of the Mediterranean: these orographic constraints and the thermal contrast between land and sea give rise to specific local effects that influence the general circulation of both atmosphere and ocean.
The main hydrodynamics characteristics are a pronounced cyclonic circulation involving both the superficial MAW and the lower LIW layer which is fed by two main currents flowing along the Corsican coast towards North. Although this structure is almost permanent, it shows an important seasonal and interannual variability due to the variability of the Tyrrhenian current flowing through the Corsica channel.
Moreover, the Ligurian basin is very important for many physical and biological aspects. During the winter, processes of dense water formation often occur. Its productivity is very high and its ecosystem very rich and complex. The strong air-sea interaction processes greatly affect both atmospheric and marine circulation, determining a strong variability in the upper ocean thermal gradient.
The circulation and the most important processes of the Ligurian basin are mainly influenced by the local atmospheric-climatological conditions, which, in their turn, depend on planetary oscillations (e.g., tight relationship between the water fluxes in the Corsica channel and the NAO variability)[Astraldi and Gasperini (1992)], [Vignudelli et al.(1999)].
As for the biological and marine living aspects, the richness and variety of populations found in the basin induced the coastal governments to sign an international treaty for the delimitation of an area (the so-called 'Cetacean Sanctuary'), mostly centered on the Ligurian Sea, dedicated to the preservation and study of the existing species. It must be stressed that the Ligurian Sea can be clearly distinguished from all the other basins in the Mediterranean as to the number and variety of great pelagic fishes and mammals. Cetaceans, Dolphins, Swordfish, Tuna that are present in the offshore waters, form the upper level of an ecosystem distributed over a water column of more than 2000 m and strongly diversified as far as the planktonic components. Along the zooplankton trophic chains, this richness manifests itself with an abundance of the same species of krill that is present in the North-Atlantic (Meganyctyphanes Norvegica), representing a key-species in the trophic chains of large pelagic, directly (fin whales, young tuna, etc.) or indirectly (sperm whales, swordfish, etc.). Very recent studies have shown that the Ligurian Sea is the region where the Mediterranean fin whales are born, thus indicating very favourable conditions for their living, which do not exist in any other part of the Mediterranean.