Mediterranean Sea

Mediterranean Sea, inland sea of Europe, Asia, and Africa, linked to the Atlantic Ocean at its western end by the Strait of Gibraltar. Known to the Romans as Mare Nostrum (our sea), the Mediterranean is almost landlocked. It is of great political importance as a maritime outlet for the countries of the former Union of Soviet Socialist Republics, via the Bosporus, Sea of Marmara, Dardanelles, and Black Sea, and for European and American access to the petroleum of Libya and Algeria and the Persian Gulf region, via the Suez Canal and overland pipelines.

The Mediterranean Sea covers an area of about 2,510,000 sq km (969,000 sq mi). It has an eastern to western extent of some 3,860 km (2,400 mi) and a maximum width of about 1,600 km (1,000 mi). Generally shallow, with an average depth of 1,500 m (4,926 ft), it reaches a maximum depth of 5,150 m (16,896 ft) off the southern coast of Greece.

The Mediterranean is a remnant of the vast ancient sea called Tethys, which was squeezed almost shut in a tectonic episode of the Oligocene Epoch, 30 million years ago, when the crustal plates carrying Africa and Eurasia collided. The plates are still grinding together, causing the eruption of volcanoes such as Etna, Vesuvius, and Stromboli, all in Italy, and triggering frequent earthquakes, which have devastated parts of Italy, Greece, and Turkey.

Geological evidence has shown that sometime between five and six million years ago the Mediterranean became isolated from the Atlantic Ocean, causing the sea water to evaporate, and leaving immense dried-up basins. Also known as the Messinian Salinity Crisis, evidence shows a large accumulation of salt deposits sandwiched between deep-water marine sediments. It would have been impossible for marine organisms to survive in such salty conditions, and it is the lack of marine fossils that has made the crisis, and following inundation, difficult to date. However, it is generally thought that the Mediterranean evaporated gradually, and that a dramatic increase in sea level caused it to refill relatively quickly. New developments in astrochronology have dated the isolation of the Mediterranean at 5.59 million years ago and its refilling at 5.33 million years ago.

An undersea sill from Tunisia to Sicily divides the Mediterranean into eastern and western basins. Another seafloor sill, from Spain to Morocco, lies at the outlet of the Mediterranean. Only 300 m (1,000 ft) deep, it restricts circulation through the narrow Strait of Gibraltar, thereby greatly reducing the tidal range of the sea and, coupled with high rates of evaporation, making the Mediterranean much saltier than the Atlantic Ocean.

Malta and Sicily have commanded shipping through the strategically located Straits of Sicily and Messina. Other important islands include the Balearic Islands (Spain); Corsica (France); Sardinia (Italy); Cyprus; and the Ionian, Cyclades, Dodecanese, and Aegean islands (Greece). Arms of the Mediterranean include the Tyrrhenian Sea (located off western Italy), the Adriatic Sea (between Italy and the Balkan Peninsula), and the Aegean and Ionian seas (off peninsular Greece). Barcelona, Marseille, Genoa, Trieste, Alexandria, and Haifa are important seaports in the region. Major rivers entering the Mediterranean are the Ebro, Rhône, Po, and Nile.