The Canary Current is a wind-driven surface current that is part of the

North Atlantic Gyre The North Atlantic Gyre of the Atlantic Ocean is one of five great oceanic gyres. It is a circular ocean current, with offshoot eddies and sub-gyres, across the North Atlantic from the Intertropical Convergence Zone (calms or doldrums) to the part ...

. This eastern boundary current branches south from the North Atlantic Current and flows southwest about as far as Senegal where it turns west and later joins the Atlantic North Equatorial Current. The current is named after the

Canary Islands The Canary Islands (; es, Canarias, ), also known informally as the Canaries, are a Spanish autonomous community and archipelago in the Atlantic Ocean, in Macaronesia. At their closest point to the African mainland, they are west of Morocc ...

. The archipelago partially blocks the flow of the Canary Current (Gyory, 2007). This wide and slow moving current is thought to have been exploited in the early Phoenician navigation and settlement along the coast of western Morocco. The ancient Phoenicians not only exploited numerous fisheries within this current zone, but also established a factory at Iles Purpuraires off present day

Essaouira Essaouira ( ; ar, الصويرة, aṣ-Ṣawīra; shi, ⵜⴰⵚⵚⵓⵔⵜ, Taṣṣort, formerly ''Amegdul''), known until the 1960s as Mogador, is a port city in the western Moroccan region of Marakesh-Safi, on the Atlantic coast. It ha ...

for extracting a Tyrian purple dye from a marine gastropod murex species.

Upwelling

A prominent feature of Eastern Boundary Currents is the presence of upwelling.

Ekman drift Ekman transport is part of Ekman motion theory, first investigated in 1902 by Vagn Walfrid Ekman. Winds are the main source of energy for ocean circulation, and Ekman Transport is a component of wind-driven ocean current. Ekman transport occurs ...

causes offshore transport of surface waters, which are then replaced with deep water from below. Deep waters are cold and

nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...

-rich and have a key role in stimulating primary productivity. Upwelling has led to the enhancement of coastal fisheries in western Morocco (Hance, 1975). Upwelling, with its consequent chilling on affected seas, also gives near-shore land areas a more temperate microclimate because any air of tropical origin which passes over the chilly water is cooled at its surface level. Major upwelling occurs between 23 and 25 degrees northern latitude (Canary Current, 2002). Upwelling occurs year-round at Cap Blanc ( Ras Nouadhibou) and northward. South of Cap Blanc, upwelling is limited to winter and spring due to the northward migration of the

Azores High The Azores High also known as North Atlantic (Subtropical) High/Anticyclone or the Bermuda-Azores High, is a large subtropical semi-permanent centre of high atmospheric pressure typically found south of the Azores in the Atlantic Ocean, at the Hor ...

during summer, which is responsible for driving equatorward winds. Minas ''et al.'' (1982) showed that at the latitude of Cap Blanc, a front exists that separates North Atlantic Central Water (NACW) and South Atlantic Central Water (SACW). SACW, to the south of Cap Blanc, is richer in nutrients than NACW. A poleward subsurface counter-current is responsible for bringing SACW to the Cap Blanc region resulting in maximal primary production. Primary production to the north is limited by nutrient availability in NACW. Primary production to the south of Cap Blanc is limited by the occurrence of upwelling events.

Upwelling and primary production

Huntsman and Barber (1977) hypothesized that high productivity results from alternating upwelling events and relatively calm periods. Upwelling is necessary to bring the nutrients to the surface but if the event is sustained for a long period of time, it is tough for

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. Ph ...

to remain in the euphotic zone. Calm periods allow for stratification to develop, which means that phytoplankton can grow and multiply while held in the shallow mixed layer. In other words, there is a miniature spring bloom during each calm period (Mann & Lazier, 1996).

Upwelling and zooplankton

Upwelling and primary production follow the onset of a strong wind within a few days (Mann & Lazier, 1996). Zooplankton, such as

copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...

s, take longer to respond to the abundance of food available because they have life cycles of weeks rather than days. Zooplankton in the Canary Current reach their peak density in autumn when upwelling intensity decreases. The decrease in upwelling allows the zooplankton to stay over the shelf where their food supply exists. Due to the rapid response of phytoplankton to upwelled nutrients, zooplankton are seldom food-limited.

Upwelling and fish

Four types of fish comprise 75% of total catch in the Cap Blanc region (Mann & Lazier, 1996).

Clupeid Clupeidae is a family of ray-finned fishes, comprising, for instance, the herrings, shads, sardines, hilsa, and menhadens. The clupeoids include many of the most important food fishes in the world, and are also commonly caught for production of f ...

s (''Sardina pilchardus'', the sardine, and ''Sardinella aurita'') were the most abundant. ''S. pilchards'' dominate in the cooler northern waters while ''S. aurita'' are prevalent in warmer southern waters. Next most abundant were

Jack mackerel Jack mackerels or saurels are marine fish in the genus ''Trachurus'' of the family Carangidae. The name of the genus derives from the Greek words ''trachys'' ("rough") and ''oura'' ("tail"). Some species, such as ''T. murphyi'', are harvested in ...

(''Trachurus'' spp.) and Redfish (Sparidae). Ansa-Emmin (1982) found that in 1974, the total fish landings reached 2.68 million tons. Nearly 1 million tons were Clupeidae with .67 million tons being sardines.

Nutrient recycling

Phytoplankton over the shelf area either sink to the bottom or are consumed by zooplankton. If they settle to the bottom, phytoplankton release ammonia during their decomposition, which returns nitrogen to the waters. Consequently, the phytoplankton remains could be consumed by

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

dwellers, which also excrete ammonia. If consumed by zooplankton, nitrogen from the phytoplankton will be returned to the environment via excreted ammonia or fecal pellets, which settle to the bottom. Regardless of the mechanism, a high proportion of phytoplankton nitrogen ends up being released in the shoreward-moving lower layer of the water column (Mann & Lazier, 1996). This water will later be upwelled and can stimulate further primary production. Barber and Smith (1981) estimated that on the shelf off Cap Blanc, regenerated nitrogen accounted for 72% of total nitrogen.

References

* Ansa-Emmin, M. (1982) Fisheries in the CINECA region. ''Rapp. P.-v. Reun. Cons. Int. Explor. Mer.'' 180: 405-422. * Barber, R.T. and Smith R.L. (1981) Coastal upwelling ecosystems. pp 31–68. In: A.R. Longhurst (Ed) ''Analysis of Marine Ecosystems''. Academic Press, New York. 741 pp. * C.Michael Hogan, ''Mogador: Promontory Fort'', The Megalithic Portal, ed. Andy Burnham, November 2, 200

Canary Current (2002)
* Huntsman, S.A. and Barber, R.T. (1977) Primary production off northwest Africa: the relationship to wind and nutrient conditions. ''Deep-Sea Research''. 24: 25-33.

* Mann, K. H., and J. R. N. Lazier. Dynamics of Marine Ecosystems: Biological-physical Interactions in the Oceans. Boston: Blackwell Science, 1996. Print. * Minas, H.J., Codispoti, L.A. and Dugdale, R.C. (1982) Nutrients and primary production in the upwelling region off northwest Africa.'' Rapp. P.-v. Reún. Cons. Int. Explor. Mer.'' 180: 148-183. * William Adams Hance (1975) ''The Geography of Modern Africa'', Columbia University Press,

External links

Encyclopedia of Earth: Canary Current

Canary Current Large Marine Ecosystem (CCLME) project
{{Ocean Marine ecoregions Currents of the Atlantic Ocean