1 The African Marginal and Enclosed Seas: An Overview
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of “concentration” basins. Hence, salinity is higher than in the outer ocean, while
water exchange in the connecting channels consists of an upper layer inflow of fresher
oceanic water and a lower layer outflow of saltier water. In addition, a number of
inland basins, the African Great Lakes, or Rift Valley Lakes, should also be included
among the major water bodies of the African continent. By the same token, some of
the areas impacted by the Nile River, connecting the Great Lakes in the highlands
of sub-equatorial east Africa and the Mediterranean Sea, across the eastern Sahara
desert, and forming a wide delta dotted by brackish lagoons, should also be numbered
among the “coastal” features of interest here.
The African Seas comprise a wide spectrum of different ecosystems, spanning
most of the Earth climatic zones, and ranging from unspoiled conditions to pollution
hotspots heavily impacted by human activities. Exploring the wide spectrum of
environmental features and processes of such a varied collection of marine and coastal
(and inland) regions is vital for the assessment of the abundant natural resources that
the African Seas have to offer – of those in dire need of being more sustainably
exploited, for the well being of continental economies and societies, and of the
others that should be protected and maintained in their still pristine conditions.
Due to their vast area, great depth and efficient water circulation, the open oceans
are relatively unaffected by human activities, compared with marginal and enclosed
basins. Hence, degradation is limited to near-coastal zones, while most of the Atlantic
and Indian ecosystems remain undisturbed, even though with notable exceptions.
The deterioration of fish stocks, the reasons for which are not yet fully understood
but could include overfishing and climatic variability, is an example of the severe
problems hampering the development potential offered by existing oceanic resources.
The state of the Red Sea and the (southern) Mediterranean Sea, which have limited
exchanges with the adjacent oceans, is extremely varied and strongly influenced by
local processes.
In the following, the main geographic features of the oceanic areas surrounding the
African continent will be recalled, focusing in particular on some key oceanographic
features of the marginal basins dominated by major surface current systems. The
latter, in fact, influence physical as well as ecological processes of entire near-coastal
regions, providing at the same time a critical contribution to regulation of the world’s
climate. In addition, the environmental traits of the Mediterranean Sea and of the
Red Sea (and of the main Great Lakes as well) shall be reviewed in some detail, in
order to introduce the peculiarities and special challenges of these basins that require
more in-depth presentations.
1.2 Atlantic Ocean African Waters
The Atlantic Ocean, connecting all of the marginal basins west of the African continent, is the second largest of the Earth’s oceanic divisions. It began to form about 150
million years ago, in the Jurassic period, when a rift opened up in the supercontinent of
Gondwana, resulting in the separation of Africa and South America. The separation
continues today along the Mid-Atlantic Ridge at a rate of about 2.5 cm/year.
5
of “concentration” basins. Hence, salinity is higher than in the outer ocean, while
water exchange in the connecting channels consists of an upper layer inflow of fresher
oceanic water and a lower layer outflow of saltier water. In addition, a number of
inland basins, the African Great Lakes, or Rift Valley Lakes, should also be included
among the major water bodies of the African continent. By the same token, some of
the areas impacted by the Nile River, connecting the Great Lakes in the highlands
of sub-equatorial east Africa and the Mediterranean Sea, across the eastern Sahara
desert, and forming a wide delta dotted by brackish lagoons, should also be numbered
among the “coastal” features of interest here.
The African Seas comprise a wide spectrum of different ecosystems, spanning
most of the Earth climatic zones, and ranging from unspoiled conditions to pollution
hotspots heavily impacted by human activities. Exploring the wide spectrum of
environmental features and processes of such a varied collection of marine and coastal
(and inland) regions is vital for the assessment of the abundant natural resources that
the African Seas have to offer – of those in dire need of being more sustainably
exploited, for the well being of continental economies and societies, and of the
others that should be protected and maintained in their still pristine conditions.
Due to their vast area, great depth and efficient water circulation, the open oceans
are relatively unaffected by human activities, compared with marginal and enclosed
basins. Hence, degradation is limited to near-coastal zones, while most of the Atlantic
and Indian ecosystems remain undisturbed, even though with notable exceptions.
The deterioration of fish stocks, the reasons for which are not yet fully understood
but could include overfishing and climatic variability, is an example of the severe
problems hampering the development potential offered by existing oceanic resources.
The state of the Red Sea and the (southern) Mediterranean Sea, which have limited
exchanges with the adjacent oceans, is extremely varied and strongly influenced by
local processes.
In the following, the main geographic features of the oceanic areas surrounding the
African continent will be recalled, focusing in particular on some key oceanographic
features of the marginal basins dominated by major surface current systems. The
latter, in fact, influence physical as well as ecological processes of entire near-coastal
regions, providing at the same time a critical contribution to regulation of the world’s
climate. In addition, the environmental traits of the Mediterranean Sea and of the
Red Sea (and of the main Great Lakes as well) shall be reviewed in some detail, in
order to introduce the peculiarities and special challenges of these basins that require
more in-depth presentations.
1.2 Atlantic Ocean African Waters
The Atlantic Ocean, connecting all of the marginal basins west of the African continent, is the second largest of the Earth’s oceanic divisions. It began to form about 150
million years ago, in the Jurassic period, when a rift opened up in the supercontinent of
Gondwana, resulting in the separation of Africa and South America. The separation
continues today along the Mid-Atlantic Ridge at a rate of about 2.5 cm/year.