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An introduction to Mediterranean deep-sea biology* - page 2 / 32





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and the book “The Mediterranean Sea: A Natural Sedimentation Laboratory” edited by Stanley (1972), the International Bathymetric Chart of the Mediterranean (IBCM) of 1981 published by the USSR Ministry of Defence under the auspices of UNESCO, and the book “Geological Evolution of the Mediterranean Basin” edited by Stanley and Wezel (1985). The IBCM bathymetric contours and coastlines were incorporated into the worldwide digital atlas, the General Bathymetric Chart of the Oceans (GEBCO), drawn up by the British Oceano- graphic Data Centre (BODC). At present, the Inter- national Hydrographic Organisation (IHO) has assigned new areas of responsibility to the national hydrographic offices to obtain new detailed bathy- metric maps using multibeam and long-range side- scan sonars. In some specific areas, regional geolog- ical work has made an important contribution to knowledge of the physiography and seafloor charac- teristics of the Mediterranean Sea: Pierrot (1972) for the Ligure Sea, Monti et al. (1978) for the western basin, Gennesaux and Vanney (1979) for the Algero-Provençal basin, Canals et al. (1982) for the northeastern Iberian margin, Bellaiche et al. (1980) for the deep-sea fan of the Rhone river, Canals et al. (2000) for the Valencia trough, and Berné et al. (1999 and 2002) for the Gulf of Lions.

The Mediterranean sea occupies an elongated basin, which was formerly part of the ancient Tethys Sea. It is 4000 km in length, and is located between 30º and 46º N and 5.50º W and 36º E (excluding the Black Sea).

The western limit of the Mediterranean, the Strait of Gibraltar, is a shallow and narrow channel 320 m deep and 14 km wide and the only (natural) connec- tion with the Atlantic Ocean. The northeastern limit connects the Mediterranean Sea to the Black Sea through the shallow and narrow channel in the Dar- danelles, where the sill depth is 70 m. The Mediter- ranean Sea and the Red Sea have been connected since 1869 by the Suez Canal.

Morphologically the Mediterranean Basin is subdivided by a series of transverse ridges with a north-south trend, parts of which emerge above sea level (Sverdrup et al., 1942). A submarine ridge between the island of Sicily and the African coast affects the primary division into the western and the eastern depressions. The sill depth in the strait between Sicily and Tunis is about 400 m.

The western part is subdivided into three main submarine basins. The Alboran Basin is east of the Gibraltar Strait, between the coasts of Spain and

8 F. SARDÀ et al.

Morocco. The Balearic Basin or Algero-Provençal Basin, east of the Alboran Basin, is west of Sardinia and Corsica, extending from off the coast of Algeria to Provence in France. The Tyrrhenian Basin lies between the peninsula of Italy and the islands of Corsica and Sardinia .

The eastern Mediterranean is subdivided into two major basins. The Ionian Basin lies between the south of Italy and Greece and the coast of Libya, an area known as the Ionian Sea. A submarine ridge between western Crete and Barqah (Lybia) separates the Ionian Basin from the Levantine Basin to the south of Asia Minor. The Ionian Sea shows the deepest recorded point in the Mediterranean Sea, with 5121 m depth at the Hellenic Trough west of the submarine ridge (Vanney and Gennessaux, 1985). The island of Crete separate the Levantine Basin from the Aegean Sea, which comprises the area to the north of Crete and is bounded to the north and west by the coast of Greece and to the east by the coast of Turkey. The Adriatic Sea is a “cul-de- sac” basin (Vanney and Genesseaux, 1985) connect- ed to the main water body by the Strait of Otranto, and is bounded by the peninsula of Italy to the west and north and by Croatia and Albania to the east.

Geological structure

The present-day structure of the Mediterranean basin results from the overall convergence of Africa and Eurasia, which involved several successive local rifting processes and collisions during the Ter- tiary.

In the eastern Mediterranean, part of the conver- gence is still accommodated by northward subduc- tion Mesozoic Thetynian oceanic crust (Séranne, 1999). The active subduction in the Hellenic Trench system illustrates the final fragments of the Tethys Ocean, which may be in the latest stages of subduc- tion below the European plate (Maldonado, 1985). In contrast, the western Mediterranean is floored by oceanic crust formed by extensional rifting during the Cenozoic time. This extensional basin was formed simultaneously with thrusting and mountain building in the surrounding areas, during continued northward motion of the African plate in relation to the Eurasian plate (Séranne, 1999).

The oldest Cenozoic basin of the Mediterranean Sea is the Balearic Basin, dating back to latest Oligocene or earliest Miocene from 28 to 5 Ma. The youngest basin is the Aegean Sea in the eastern Mediterranean, which mostly developed during the

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