interests of fishery. The ATC shows a specific path in winter while the route is less clearly-marked during summer. The last common used scale is the large Mediterranean Basin scale which includes the thermohaline circulation. The thermohaline circulation in the Strait of Sicily is anti-estuarine and is driven by, at one site, the fresh waters entering from the Gibraltar Strait and on the other side, the negative freshwater budget from the Mediterranean Basin. Also the westward LIW in the intermediate layer and less saltier eastward Atlantic water on top are considered in this scale. The outflow of dense-water-masses characteristics of the Strait of Sicily are not stable but have been found to change interannually. Also the thermohaline circulation showed changes in structure and stratification. These changes were caused by deep water formed in the Aegean Sea which replaced the water formed in the Adriatic during the 1990s. This dense water caused enhanced salinity and temperatures in the Aegean Sea for a few years creating the deep/mediate Mediterranean overturning perturbation which has been given the name of Eastern Mediterranean Transient (EMT). The EMT is the major perturbation of the circulation and water mass aspects in this area since systematic observational data is available (1950s). The effect of the EMT on the Strait of Sicily was a freshening of the surface waters. Another important circulation mechanism that exists in the Strait of Sicily is the Biomodal Oscillating System (BiOS) Which is a feedback mechanism between the Ionic and the Adriatic sea. The thermohaline properties of the Adriatic Sea show quasi-decadal oscillations that are related to the circulation of the Ionian Sea. The upper-layer of the northern Ionian Sea shows circulations that vary between a cyclonic movement, corresponding advection of waters from the Eastern Mediterranean with very saline waters and low nutrients (oligotrophic water), and anticyclonic movement which results in saline and copiotroph (nutrient-rich) waters from the Western Mediterranean towards the Adriatic. The density of the dense waters that flow from the Adriatic Sea into the northern Ionian Sea highly depends on the type of circulation (cyclonic, or anticyclonic) in the Ionian Sea and at the other hand influences the vorticity in the Ionian Sea itself resulting in a feedback mechanism. BiOS is one of the dominant mechanisms influencing biochemical processes in the Adriatic and therefore has great impact on the organisms within this sea and in the strait. Levantine intermediate water circulation