MAP Technical Reports Series No. 106 UNEP

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in view of the projected population increase (cf. Chpt. 5) and its related activities, these problems
will become aggravated over the next 25 years.
However, it follows also that though coastal eutrophication in the Mediterranean is a
widespread problem, it can be brought under control if the political will exists to take the
necessary measures.
5. EXTENT OF EUTROPHICATION AND ALGAL BLOOMS IN THE MEDITERRANEAN
5.1 General description of the Mediterranean
The Mediterranean is an intercontinental sea. On the north, it laps the coasts of
southern Europe, on the south North Africa and on the east Asia Minor. The Italian peninsula and
Sicily divide the Mediterranean into two basins, the west and the east, communicating through
the channel of Sicily. The length of the main east-west axis is 3,860 km.; although the average
width is not over 700 km, maximum width is approx. 1,800 km. The average depth of the
Mediterranean has been estimated to be 1,502 meters. The greatest depth is found at the
Matapan trench, located in the eastern basin, at 4,632 meters. In the western basin, maximum
depth is southwest of the Island of Ponza (Tyrrhenian Sea), at 3,731 meters, cf. Table 19.
Excluding the Black Sea, the area of the Mediterranean is 2,556,000 square kilometers.
Compared to other oceans, the Atlantic for example, which has a surface of 85,620,000 square
kilometers, the extension of the Mediterranean Sea basin ranges among those of modest
dimensions.
Given the latitude at which the Mediterranean is located, the temperature of the surface
waters varies significantly with seasons. Temperature variations and rang ranges are more
marked on the northern side of the basin, less on the southern and eastern parts. The difference
in temperature in the northwest Adriatic is significant; a variation of 24EC can be measured
between winter lows (+4EC) and summer highs (+28EC).
Due to strong evaporation and to limited fluvial input, the average salinity is generally
much higher than in the other oceans. Around Gibraltar, the salinity is near 36 per thousand; as
one moves eastward, the average salinity increases, reaching a level of 39.5 in the eastern
basin. The high level of evaporation not compensated by fluvial or meteorological inputs leads
to a positive exchange balance with mostly surface inflow of waters from the Atlantic. As far as
a total estimate of inflow (Atlantic and Black Sea inputs, fluvial input, precipitation), and outflow
(evaporation, Mediterranean outputs to the Atlantic and Black Sea) is concerned, see Table 19.
Accordingly, the hydrological balance is principally maintained by the inflow of masses of
oceanic water entering from the Strait of Gibraltar.
Due to this inflow and the earth's rotation, an anti-clockwise current is generated which,
on the south side of the basin, moves from west to east, and in the opposite direction on the
north side. Due to the basin conformation, there are secondary eddies in the Tyrrhenian, the
Aegean and the Adriatic, moving in an anti-clockwise direction as well. However, in the Alboran
Sea modified atlantic waters move mostly clockwise, and waters are slit to form the Almeria-ran
jet (cf. below). In the Adriatic the abstraction of Mediterranean waters is activated mainly by
density currents generated by fluvial inputs (Po, etc.) into the northwestern part of the basin.