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3 Circulation System

Circulation inside the Sicily Channel is the consequence of the different hydrodynamic
mechanisms affecting the region delimited by Tunisia, the Sardinia Channel and the Straits
of Sicily as well as it is the results of those hydrodynamic processes inside the eastern Basin.
The region offshore the North Tunisia coast forms the junction of three major subsets in the
Mediterranean: the Algéro-Provençal Basin on the west, the Tyrrhenian Sea on the north and
the East Mediterranean on the east (Ionian Basin). The transfers of water masses from one
of these subsets towards the other are controlled by this common region. The water with an
Atlantic origin (MAW) flows from the Algerian current through the Sardinia Channel and
enters into the Sicily Channel through the Sicily Strait.

The Sicilian Channel is a high-energy site with a dynamic current system that exchanges the
waters between the Mediterranean western and eastern basins and, as we have seen above,
the influence of the strait geometry on the dynamics is very important.
Dynamically, the circulation in the Sicilian Channel can be described as an exchange of three
main water masses (Fig. 7):

 The upper layer fresh modified Atlantic water (MAW), which enters through the Sicily
channel as an extension of the north African Algerian coastal current and flows
eastward, its northernmost branch is generally known as Atlantic-Ionian Stream
(AIS);

 The Levantine Intermediate Water (LIW) that flows in the opposite direction mainly
entering through the Medina sill to the southeast of Malta and, below the LIW;

 The Eastern Mediterranean Deep Water (EMDW) which, together with the LIW, forms
the deeper eastern overflow water (EOW),

The general circulation is dictated by the slow basin scale (vertical) thermohaline structure of
the Mediterranean, and carries a significant seasonal and inter-annual variability. In the
upper thermocline the AIS characterizes the circulation by energetic meandering. The
circulation is further modified by strong mesoscale signals in the form of eddy, meander and
filament patterns.

These mesoscale processes are triggered by the synoptic scale atmospheric forcing. The
heat and momentum fluxes at the air-sea interface represent the dominant factor in the
mixing and pre-conditioning of the MAW on its way to the eastern Mediterranean.

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