1 The African Marginal and Enclosed Seas: An Overview
23
are part of the (White) Nile River basin. Lake Kivu empties into the Ruzizi River,
which flows southwards into Lake Tanganyika. Lake Victoria (68,800 km
2 , elevation
1,134 m) is the largest lake in Africa. However, it is not in the rift valley: rather, it
occupies a depression between the eastern and western rifts, formed by the uplift of
the rifts to either side. Together with Lake Tanganyika and Lake Malawi, all located in
the area, these lakes are collectively known as the African Great Lakes. The Western
Rift Valley Lakes are all freshwater lakes and home to an extraordinary number of
species (including about 1,500 cichlid fish – Cichlidae – species). Lake Tanganyika
(32,000 km
2 , elevation 773 m) is the largest and deepest (more than 1,400 m) of all
Rift Valley lakes, and is the second deepest fresh water lake on the planet (after Lake
Baikal). Below 200 m, its water is anoxic and devoid of large aquatic life. It is part
of the Congo River basin, feeding into the River Congo via the Lukuga River.
The Southern Rift Valley lakes are similar to the Western Rift Valley lakes in
that, with one exception, they are all freshwater lakes. Lake Malawi (30,000 km
2 ,
elevation 500 m), also known as Lake Nyasa, is the second largest and second deepest
(over 700 m) of the Rift Valley lakes. It is drained by the Shire River, a tributary of
the Zambezi River.
1.7 Outlook
The marginal and enclosed basins surrounding the African continent present a great
variety of environmental conditions. While some of the African Seas have been
sailed since ancient times, others remain surprisingly uncharted, in particular from
the scientific point of view. As seen earlier, the dynamics of the marginal seas around
Africa are still the subject of different, sometimes contrasting, interpretation (see
e.g. the issue of western boundary current vs train of anticyclonic eddies in the
Mozambique Channel). The biological response to such physical forcing also remains
to be fully understood (as e.g. in the case of the so-called Benguela Niño). The
exploration of these marginal seas – aiming to exploit their natural resources and
protect their ecological balance, but also to understand their role in shaping the
global climate – requires the adoption of appropriate observation systems. Data
collection with traditional surface measurements remains an key component of much
environmental research dealing with these regions. However, the need to assess the
large scales typical of most marine processes, and the prohibitive cost of lengthy,
repeated oceanographic expeditions – not to mention the recurrence of piracy and
political unrest in several coastal countries – has determined, in recent years, a
substantial undersampling of field data.
Remote sensing from Earth’s orbit can complement more conventional in situ data
gathering techniques in mapping the interaction of physical and bio-geo-chemical
processes, at the large space scales and over the long time periods required in the
African Seas. The environmental indicators measured from satellite remote sensors
allow exploring the relationships of natural settings, water dynamics, basic ecological mechanisms and their driving forces, as well as anthropogenic impacts on coastal
23
are part of the (White) Nile River basin. Lake Kivu empties into the Ruzizi River,
which flows southwards into Lake Tanganyika. Lake Victoria (68,800 km
2 , elevation
1,134 m) is the largest lake in Africa. However, it is not in the rift valley: rather, it
occupies a depression between the eastern and western rifts, formed by the uplift of
the rifts to either side. Together with Lake Tanganyika and Lake Malawi, all located in
the area, these lakes are collectively known as the African Great Lakes. The Western
Rift Valley Lakes are all freshwater lakes and home to an extraordinary number of
species (including about 1,500 cichlid fish – Cichlidae – species). Lake Tanganyika
(32,000 km
2 , elevation 773 m) is the largest and deepest (more than 1,400 m) of all
Rift Valley lakes, and is the second deepest fresh water lake on the planet (after Lake
Baikal). Below 200 m, its water is anoxic and devoid of large aquatic life. It is part
of the Congo River basin, feeding into the River Congo via the Lukuga River.
The Southern Rift Valley lakes are similar to the Western Rift Valley lakes in
that, with one exception, they are all freshwater lakes. Lake Malawi (30,000 km
2 ,
elevation 500 m), also known as Lake Nyasa, is the second largest and second deepest
(over 700 m) of the Rift Valley lakes. It is drained by the Shire River, a tributary of
the Zambezi River.
1.7 Outlook
The marginal and enclosed basins surrounding the African continent present a great
variety of environmental conditions. While some of the African Seas have been
sailed since ancient times, others remain surprisingly uncharted, in particular from
the scientific point of view. As seen earlier, the dynamics of the marginal seas around
Africa are still the subject of different, sometimes contrasting, interpretation (see
e.g. the issue of western boundary current vs train of anticyclonic eddies in the
Mozambique Channel). The biological response to such physical forcing also remains
to be fully understood (as e.g. in the case of the so-called Benguela Niño). The
exploration of these marginal seas – aiming to exploit their natural resources and
protect their ecological balance, but also to understand their role in shaping the
global climate – requires the adoption of appropriate observation systems. Data
collection with traditional surface measurements remains an key component of much
environmental research dealing with these regions. However, the need to assess the
large scales typical of most marine processes, and the prohibitive cost of lengthy,
repeated oceanographic expeditions – not to mention the recurrence of piracy and
political unrest in several coastal countries – has determined, in recent years, a
substantial undersampling of field data.
Remote sensing from Earth’s orbit can complement more conventional in situ data
gathering techniques in mapping the interaction of physical and bio-geo-chemical
processes, at the large space scales and over the long time periods required in the
African Seas. The environmental indicators measured from satellite remote sensors
allow exploring the relationships of natural settings, water dynamics, basic ecological mechanisms and their driving forces, as well as anthropogenic impacts on coastal