8
V. Barale
strong winds within a few days. Secondary producers, i.e. zooplankton, take longer
to respond to the increased availability of food, because they have life cycles of weeks
rather than days. In the Canary Current, secondary production reaches its peak in fall,
when upwelling intensity decreases, allowing zooplankton to remain over the shelf
and exploit the available food supply. Due to the rapid response of phytoplankton
to upwelled nutrients, zooplankton are seldom food-limited. The high productivity
of the Canary Current has led to the development of sizeable coastal fisheries (e.g.
in western Morocco). Four types of fish comprise about 75 % of total catches in the
Cap Blanc area. Clupeids are the most abundant, with Sardina pilchardus, the common sardine, dominating in cooler northern waters and Sardinella aurita in warmer
southern waters.
The Guinea Current flows (south) eastward at approximately 3
◦ N along the
coast of equatorial West Africa and into the Gulf of Guinea. This warm, highly
saline water body is always located north of the equator, but changes position and
intensity with the seasons. Its (westernmost) northern reach may vary between a
boreal winter minimum and summer maximum. The seasonal instability of its major
sources, the North Equatorial Countercurrent and the Canary Current, can affect this
variability. Like other boundary currents of the eastern Atlantic Ocean, the Guinea
Current is characterized by areas of upwelling and increased productivity. Cooler
waters at the surface are associated with the (boreal) summer intensification of the
current. The current is geostrophically balanced, with isotherms that slope upwards
towards the coast to the north. As the current intensifies, the slope steepens, bringing
the thermocline closer to the surface near the coast. Thus, in the Guinea Current
(in which the seasonal shallowing of the thermocline may be linked to geostrophic
adjustment of isotherms, Kelvin waves and cyclonic turbulent eddies, rather than
local wind stress) summer intensification and coastal upwelling are related, but the
apparent lack of correlation between surface temperature and wind patterns on a
seasonal scale renders the Gulf of Guinea quite unusual among upwelling regions.
Further south, the Angola Current forms the eastern section of a large, anticyclonic
gyre in the Gulf of Guinea. It is fed by the southward-turning waters from the north
branch of the Benguela Current and by various components of the intricate equatorial
current system, rather than the Guinea Current itself.
The Benguela Current is a broad, northward flowing ocean current that forms
the eastern portion of the South Atlantic Ocean gyre. The current extends roughly
from Cape of Good Hope in the south, at almost 35
◦ S, to the position of the AngolaBenguela Front in the north, at around 16
◦ S. Where the cold Benguela Current and
the warm, south-flowing Agulhas Current mix, off the the sothwestern African shelf,
a turbulent, stormy, but highly productive marine ecosystem, is formed. Its western,
offshore edge is ill-defined, and modulated by many eddies and meanders, but there
is a distinct thermal front between the waters associated with the current and those of
the near-coastal area. Inshore of the Benguela Current proper, the prevailing southeasterly winds drive coastal upwelling, forming the Benguela Upwelling System.
The cold, nutrient rich waters fuel high rates of phytoplankton growth, and sustain
the productive Benguela ecosystem. Variations in wind strength cause pulses of upwelling, similar to Kelvin waves, except on a reduced scale (of 10–100 km instead of
V. Barale
strong winds within a few days. Secondary producers, i.e. zooplankton, take longer
to respond to the increased availability of food, because they have life cycles of weeks
rather than days. In the Canary Current, secondary production reaches its peak in fall,
when upwelling intensity decreases, allowing zooplankton to remain over the shelf
and exploit the available food supply. Due to the rapid response of phytoplankton
to upwelled nutrients, zooplankton are seldom food-limited. The high productivity
of the Canary Current has led to the development of sizeable coastal fisheries (e.g.
in western Morocco). Four types of fish comprise about 75 % of total catches in the
Cap Blanc area. Clupeids are the most abundant, with Sardina pilchardus, the common sardine, dominating in cooler northern waters and Sardinella aurita in warmer
southern waters.
The Guinea Current flows (south) eastward at approximately 3
◦ N along the
coast of equatorial West Africa and into the Gulf of Guinea. This warm, highly
saline water body is always located north of the equator, but changes position and
intensity with the seasons. Its (westernmost) northern reach may vary between a
boreal winter minimum and summer maximum. The seasonal instability of its major
sources, the North Equatorial Countercurrent and the Canary Current, can affect this
variability. Like other boundary currents of the eastern Atlantic Ocean, the Guinea
Current is characterized by areas of upwelling and increased productivity. Cooler
waters at the surface are associated with the (boreal) summer intensification of the
current. The current is geostrophically balanced, with isotherms that slope upwards
towards the coast to the north. As the current intensifies, the slope steepens, bringing
the thermocline closer to the surface near the coast. Thus, in the Guinea Current
(in which the seasonal shallowing of the thermocline may be linked to geostrophic
adjustment of isotherms, Kelvin waves and cyclonic turbulent eddies, rather than
local wind stress) summer intensification and coastal upwelling are related, but the
apparent lack of correlation between surface temperature and wind patterns on a
seasonal scale renders the Gulf of Guinea quite unusual among upwelling regions.
Further south, the Angola Current forms the eastern section of a large, anticyclonic
gyre in the Gulf of Guinea. It is fed by the southward-turning waters from the north
branch of the Benguela Current and by various components of the intricate equatorial
current system, rather than the Guinea Current itself.
The Benguela Current is a broad, northward flowing ocean current that forms
the eastern portion of the South Atlantic Ocean gyre. The current extends roughly
from Cape of Good Hope in the south, at almost 35
◦ S, to the position of the AngolaBenguela Front in the north, at around 16
◦ S. Where the cold Benguela Current and
the warm, south-flowing Agulhas Current mix, off the the sothwestern African shelf,
a turbulent, stormy, but highly productive marine ecosystem, is formed. Its western,
offshore edge is ill-defined, and modulated by many eddies and meanders, but there
is a distinct thermal front between the waters associated with the current and those of
the near-coastal area. Inshore of the Benguela Current proper, the prevailing southeasterly winds drive coastal upwelling, forming the Benguela Upwelling System.
The cold, nutrient rich waters fuel high rates of phytoplankton growth, and sustain
the productive Benguela ecosystem. Variations in wind strength cause pulses of upwelling, similar to Kelvin waves, except on a reduced scale (of 10–100 km instead of