1 The African Marginal and Enclosed Seas: An Overview
15
the east-west direction and a maximum of 1,600 km (average around 800 km) in
the north-south direction. The greater Mediterranean basin consists of a series of
deep depressions, connected to each other, with an average depth of 1,500 m. Actual
depths vary between 2,500 and 3,500 m in western basin, and between 3,500 and
4,000 m in the eastern basin, where a maximum of 5,267 m is reached in the Calypso
Deep of the Ionian Sea. The two main basins are separated by the Sicily Channel
(with a 430 m sill depth) and the Strait of Messina (80 m), while the Strait of Otranto
(800 m) separates the Adriatic Sea from the eastern basin. The Mediterranean Sea
is connected to the Atlantic Ocean by the Strait of Gibraltar (14.3 km wide, at the
narrowest point, with a 290 m sill depth), in the west; to the Marmara Sea by the
Dardanelles (a strait 61 km long, from 1.2 to 6.0 km wide, averaging 55 m of depth),
and subsequently to the Black Sea by the Bosphorus (31 km long, from 0.7 to 3.4 km
wide, averaging 65 m of depth), in the northeast; to the Red Sea via the Suez Canal
(193.3 km long, 205 m wide and 24 m deep), in the southeast.
The Mediterranean Sea accounts for 46,000 km of coastlines, one-third of which
are due to the mainland and islands of the Aegean Sea. Several mountain ranges
(e.g. the Sierra Nevada, the Pyrenees, the Alps and Apennines, the Balkans) are
distributed along the northern side of the basin. Since these mountains mostly slope
steeply into the sea, the northern drainage basin is relatively small. And since the
southern side is mainly covered by desert, these combined factors tend to limit
the input of continental freshwater. Only a few large rivers flow directly into the
Mediterranean Sea, i.e. the Ebro (length 910 km, average discharge 426 m
3 s
−1 ), the
Po (682 km, 1540 m
3 s
−1 ) and the Rhone (813 km, 1710 m
3 s
−1 ), in the north, and
the Nile (6650 km, 2830 m
3 s
−1 ), in the south. The latter, considered together with
its main tributary, the White Nile, originating from the Great Lakes region of central Africa, is generally regarded as the longest river on the planet. Its flow rate has
been much altered by the closure of the Aswan High Dam, starting in 1964. The river
forms a wide delta on the southeastern Mediterranean coast, dotted by several coastal
lagoons of great ecological relevance. Additional contributions of continental freshwater, originating from the Azov Sea – where the main tributaries are the Don (length
1950 km, average discharge 935 m
3 s
−1 ) and the Kuban (870 km, 425 m
3 s
−1 ) – and
then from the Black Sea – main tributaries are the Danube (2860 km, 6500 m
3 s
−1 ),
the Dnieper (2290 km, 1670 m
3 s
−1 ) and the Dniester (1362 km, 310 m
3 s
−1 ) – enter
the Mediterranean basin from the Marmara Sea.
The typical Mediterranean climate, with low cloudiness and abundant sunshine, is
subject to both sub-tropical and mid-latitude weather systems, and is also influenced
by the northern mountain ranges. The region’s seasonal cycle is characterized by mild
winters, when the region receives most of its rainfall, and by relatively hot and dry
summers. Strong local winds, such as the cold, dry, northerly Bora and Mistral, and
the hot, dry southerly Scirocco, typify the region, particularly in winter. In general,
air temperature differences between winter and summer are limited to about 15
◦ C,
although local geographic and meteorological factors can result in extreme conditions
such as air temperatures up to 50
◦ C on the African coast. The mean temperature of
surface waters vary between minima of about 14–16
◦ C (west to east), in winter, and
maxima of about 20–26
◦ C (again, west to east), in summer, but the total excursion
15
the east-west direction and a maximum of 1,600 km (average around 800 km) in
the north-south direction. The greater Mediterranean basin consists of a series of
deep depressions, connected to each other, with an average depth of 1,500 m. Actual
depths vary between 2,500 and 3,500 m in western basin, and between 3,500 and
4,000 m in the eastern basin, where a maximum of 5,267 m is reached in the Calypso
Deep of the Ionian Sea. The two main basins are separated by the Sicily Channel
(with a 430 m sill depth) and the Strait of Messina (80 m), while the Strait of Otranto
(800 m) separates the Adriatic Sea from the eastern basin. The Mediterranean Sea
is connected to the Atlantic Ocean by the Strait of Gibraltar (14.3 km wide, at the
narrowest point, with a 290 m sill depth), in the west; to the Marmara Sea by the
Dardanelles (a strait 61 km long, from 1.2 to 6.0 km wide, averaging 55 m of depth),
and subsequently to the Black Sea by the Bosphorus (31 km long, from 0.7 to 3.4 km
wide, averaging 65 m of depth), in the northeast; to the Red Sea via the Suez Canal
(193.3 km long, 205 m wide and 24 m deep), in the southeast.
The Mediterranean Sea accounts for 46,000 km of coastlines, one-third of which
are due to the mainland and islands of the Aegean Sea. Several mountain ranges
(e.g. the Sierra Nevada, the Pyrenees, the Alps and Apennines, the Balkans) are
distributed along the northern side of the basin. Since these mountains mostly slope
steeply into the sea, the northern drainage basin is relatively small. And since the
southern side is mainly covered by desert, these combined factors tend to limit
the input of continental freshwater. Only a few large rivers flow directly into the
Mediterranean Sea, i.e. the Ebro (length 910 km, average discharge 426 m
3 s
−1 ), the
Po (682 km, 1540 m
3 s
−1 ) and the Rhone (813 km, 1710 m
3 s
−1 ), in the north, and
the Nile (6650 km, 2830 m
3 s
−1 ), in the south. The latter, considered together with
its main tributary, the White Nile, originating from the Great Lakes region of central Africa, is generally regarded as the longest river on the planet. Its flow rate has
been much altered by the closure of the Aswan High Dam, starting in 1964. The river
forms a wide delta on the southeastern Mediterranean coast, dotted by several coastal
lagoons of great ecological relevance. Additional contributions of continental freshwater, originating from the Azov Sea – where the main tributaries are the Don (length
1950 km, average discharge 935 m
3 s
−1 ) and the Kuban (870 km, 425 m
3 s
−1 ) – and
then from the Black Sea – main tributaries are the Danube (2860 km, 6500 m
3 s
−1 ),
the Dnieper (2290 km, 1670 m
3 s
−1 ) and the Dniester (1362 km, 310 m
3 s
−1 ) – enter
the Mediterranean basin from the Marmara Sea.
The typical Mediterranean climate, with low cloudiness and abundant sunshine, is
subject to both sub-tropical and mid-latitude weather systems, and is also influenced
by the northern mountain ranges. The region’s seasonal cycle is characterized by mild
winters, when the region receives most of its rainfall, and by relatively hot and dry
summers. Strong local winds, such as the cold, dry, northerly Bora and Mistral, and
the hot, dry southerly Scirocco, typify the region, particularly in winter. In general,
air temperature differences between winter and summer are limited to about 15
◦ C,
although local geographic and meteorological factors can result in extreme conditions
such as air temperatures up to 50
◦ C on the African coast. The mean temperature of
surface waters vary between minima of about 14–16
◦ C (west to east), in winter, and
maxima of about 20–26
◦ C (again, west to east), in summer, but the total excursion