A surface current, flowing from the south along the African coast, enters the Mediterranean through Gibraltar. Underneath, a smaller and slower current, about 305 m (1,000 ft) deep, flows into the Atlantic. Water balance is also maintained by a similar - although smaller - inflow and outflow through the Turkish straits.

The general pattern of surface currents is counterclockwise, with many local exceptions. Only at Gibraltar and on the east coast of Tunisia is the tidal range greater than 914 mm (3 ft). Surface temperatures vary seasonally, from about 5° C (41° F) in February in the northern Adriatic to 31° C (88° F) in August off the coast of Libya. Because of considerable evaporation, the water is much more saline than that of the Atlantic Ocean or the Black Sea. Salinity increases from west to east, toward the end of the dry season, and away from river mouths.

The floor of the Mediterranean is covered with yellow brown sediments-about 50% lime and the rest clay and sand - to an approximate thickness of 2,740 m (9,000 ft). Underlying this layer is blue mud. Fine riverine muds overlie these strata near river mouths and are carried great distances by currents, thus retarding the development of deltas.

The variety of climates, water depths, salinity, and landforms has produced a variety of flora and fauna, both in the sea and on its shores. More than 400 species of fish are found in the sea, along with shellfish, corals, sponges, and seaweeds. The western basin has a greater variety than the saltier eastern one. The total quantity, however, is not particularly large because of the relatively low level of phytoplankton production in the warm water.