GEOLOGICAL AND OCEANOGRAPHICAL SETTING

The Marsili volcano, also believed to be a spreading center, N100-106°[Marani and Trua(2002)], rises 3000 metres from the Marsili basin seafloor to a minimum depth of 499 m. It is elongated 60 km NNE-SSW with mean width of 16 km. A narrow, 1 km wide linear region of lower gradient, approximately bounded by the 1000 metre isobath, marks the summit zone that stretches 20 km along the main axis of the volcano. The volcano summit axis zone and tip regions are characterised by the development of linear structures arranged in segments generated mainly by the alignment of narrow, linear cone ridges, or by the linear arrangement of several circular-based cones .

**Figure 2:** Geographical setting of the Marsili Smt., elevating from the Marsili basin (>3500 m depth). Topographic and bathymetric data by [Marani, Gamberi and Bonatti(2004),Bortoluzzi et al.(1999)]
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The Tyrrhenian Sea exchanges water with the rest of the Mediterranean Sea through the Sardinia Channel, the Sicily Strait and the Corsica Channel, that represent morphologic constraints for the circulation of the intermediate and deep waters [Millot C.(1987),Astraldi and Gasparini(1994),Sparnocchia et al.(1999),Astraldi et al.(2001)]. The surface water (0-200m) entering the Tyrrhenian Sea through the Sardinia Channel is the Modified Atlantic Water (MAW) from the Algerian Current (AC). The MAW is characterized by low salinity (on average less than 38 PSU), and flows cyclonically along the italian coast. Through the Sicily Strait and deeper than 200 m down to about 700m, the basin receives the Levantine Intermediate Water (LIW), which is marked by a subsurface temperature maximum and by a higher salinity (on average 38.8 PSU), and mixes with the surface MAW and deeper water masses. From about 700 m to the bottom the Tyrrhenian Deep Water (TDW) is present, being the result of the modification of the West Mediterranean Deep Water (WMDW) that crosses the Sardinia Channel. The circulation pattern in the Tyrrhenian Sea is normally characterized by two cyclonic gyres in the south and in the northern basins, and by the presence of cyclonic and anticyclonic eddies in the central basin. Interesting features in the TDW [Zodiatis and Gasparini(1995)] are the thermoaline 'staircase' formations.