The effect of the Eastern Mediterranean Transient on the hydrographic characteristics in the Strait of Sicily and in the Tyrrhenian Sea

Recent studies have definitively shown the high sensitivity of the Mediterranean Sea to the effects produced by the large-scale atmospheric systems. The rapid response of this basin, when compared with the ocean time scales, makes the interannual variability of the circulation an important signal that, in some regions, may prevail over the annual cycle. We have also to consider that the distinct sub-basins, often subjected to different atmospheric and dynamic regimes, produce specific water masses that can reach all the Mediterranean regions as far as the adjacent Atlantic Ocean by a connecting network provided by the internal straits and channel. In this scenario an important role is played by the Strait of Sicily dividing the two principal sub-basins, the eastern and the western Mediterranean. A long-term monitoring of the hydrographic properties of water masses across this strait, initiated in the second half of the 1980s, permitted the identification of the principal interannual variations in the water exchange between the Ionian Sea and the Tyrrhenian Sea. It was possible to follow the evolution of the water mass characteristics under the influence of the climatic transient, which modified the production of both the intermediate and the deep water in the eastern Mediterranean. A consequence was an increase of density in the Sicily westward outflow, which produced a cascade in the deep Tyrrhenian with a remarkable deep injection of heat and salt. Furthermore, moving from the impact on the Tyrrhenian Sea, the possible effects on the western Mediterranean basin are discussed.