Canary Current
Encyclopedia
The Canary Current is a wind-driven surface current that is part of the North Atlantic Gyre
. 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 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 Phoenicia
n 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
for extracting a Tyrian purple
dye from a marine gastropod murex
species (Hogan, 2007).
. Ekman drift causes offshore transport of surface waters, which are then replaced with deep water from below. Deep waters are cold and Nutrient
-rich and have a key role in stimulating Primary productivity. Upwelling has led to the enhancement of coastal fisheries
in western Morocco (Hance, 1975).
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
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.
. In other words, there is a miniature spring bloom
during each calm period (Mann & Lazier, 1996).
, such as copepod
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.
, and Sardinella aurita) were the most abundant. S. pilchards dominate in the cooler northern waters while S. aurita are dominate in warmer southern waters. Next most abundant were Jack mackerel (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.
during their decomposition
, which returns nitrogen to the waters. Consequently, the phytoplankton remains could be consumed by benthic 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.
North Atlantic Gyre
The North Atlantic Gyre, located in the Atlantic Ocean, is one of the five major oceanic gyres. It includes the Gulf Stream and contains the Sargasso Sea. This gyre is similar to the North Pacific Gyre in the way it traps man-made ocean debris in the North Atlantic Garbage Patch, similar to the...
. This eastern boundary current
Boundary current
Boundary currents are ocean currents with dynamics determined by the presence of a coastline, and fall into two distinct categories: western boundary currents and eastern boundary currents.-Eastern boundary currents:...
branches south from the North Atlantic Current
North Atlantic Current
The North Atlantic Current is a powerful warm ocean current that continues the Gulf Stream northeast. West of Ireland it splits in two; one branch, the Canary Current, goes south, while the other continues north along the coast of northwestern Europe...
and flows southwest about as far as Senegal
Senegal
Senegal , officially the Republic of Senegal , is a country in western Africa. It owes its name to the Sénégal River that borders it to the east and north...
where it turns west and later joins the Atlantic North Equatorial Current
North Equatorial Current
The North Equatorial Current is a significant Pacific and Atlantic Ocean current that flows east-to-west between about 10° north and 20° north. It is the southern side of a clockwise subtropical gyre. Despite its name, the North Equatorial Current is not connected to the equator...
. The current is named after the Canary Islands
Canary Islands
The Canary Islands , also known as the Canaries , is a Spanish archipelago located just off the northwest coast of mainland Africa, 100 km west of the border between Morocco and the Western Sahara. The Canaries are a Spanish autonomous community and an outermost region of the European Union...
. The archipelago
Archipelago
An archipelago , sometimes called an island group, is a chain or cluster of islands. The word archipelago is derived from the Greek ἄρχι- – arkhi- and πέλαγος – pélagos through the Italian arcipelago...
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 Phoenicia
Phoenicia
Phoenicia , was an ancient civilization in Canaan which covered most of the western, coastal part of the Fertile Crescent. Several major Phoenician cities were built on the coastline of the Mediterranean. It was an enterprising maritime trading culture that spread across the Mediterranean from 1550...
n navigation and settlement along the coast of western Morocco
Morocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...
. The ancient Phoenicians not only exploited numerous fisheries within this current zone, but also established a factory at Iles Purpuraires
Iles Purpuraires
Iles Purpuraires are a set of small islands off the western coast of Morocco at the bay located at Essaouira. These islands were settled in antiquity by the Phoenicians, chiefly to exploit certain marine resources and as a promontory fort...
off present day Essaouira
Essaouira
Mogador redirects here, for the hamlet in Surrey see Mogador, Surrey.Essaouira is a city in the western Moroccan economic region of Marrakech-Tensift-Al Haouz, on the Atlantic coast. Since the 16th century, the city has also been known by its Portuguese name of Mogador or Mogadore...
for extracting a Tyrian purple
Tyrian purple
Tyrian purple , also known as royal purple, imperial purple or imperial dye, is a purple-red natural dye, which is extracted from sea snails, and which was possibly first produced by the ancient Phoenicians...
dye from a marine gastropod murex
Murex
Murex is a genus of medium to large sized predatory tropical sea snails. These are carnivorous marine gastropod molluscs in the family Muricidae, commonly calle "murexes" or "rock snails"...
species (Hogan, 2007).
Upwelling
A prominent feature of Eastern Boundary Currents is the presence of upwellingUpwelling
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water. The increased availability in upwelling regions results in high levels of primary...
. Ekman drift causes offshore transport of surface waters, which are then replaced with deep water from below. Deep waters are cold and Nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...
-rich and have a key role in stimulating Primary productivity. Upwelling has led to the enhancement of coastal fisheries
Fishery
Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...
in western Morocco (Hance, 1975).
Major upwelling occurs between 23
23rd parallel north
The 23rd parallel north is a circle of latitude that is 23 degrees north of the Earth's equatorial plane. It crosses Africa, Asia, the Indian Ocean, the Pacific Ocean, North America, the Caribbean and the Atlantic Ocean....
and 25 degrees northern
25th parallel north
The 25th parallel north is a circle of latitude that is 25 degrees north of the Earth's equatorial plane. It crosses Africa, Asia, the Indian Ocean, the Pacific Ocean, North America and the Atlantic Ocean....
latitude (Canary Current, 2002). Upwelling occurs year-round at Cap Blanc (Ras Nouadhibou
Ras Nouadhibou
Ras Nouadhibou is a 40-mile peninsula or headland in the African coast of the Atlantic Ocean by the Tropic of Cancer. It is internationally known as Cap Blanc in French or Cabo Blanco in Spanish .- History :...
) and northward. South of Cap Blanc, upwelling is limited to winter and spring due to the northward migration of the Azores high
Azores High
The Azores High is a large subtropical semi-permanent centre of high atmospheric pressure found near the Azores in the Atlantic Ocean, at the Horse latitudes...
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 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 layerMixed layer
The oceanic or limnological mixed layer is a layer in which active turbulence has homogenized some range of depths. The surface mixed layer is a layer where this turbulence is generated by winds, cooling, or processes such as evaporation or sea ice formation which result in an increase in salinity...
. In other words, there is a miniature spring bloom
Spring bloom
The spring bloom is a strong increase in phytoplankton abundance that typically occurs in the early spring and lasts until late spring or early summer. This seasonal event is characteristic of temperate North Atlantic, sub-polar, and coastal waters...
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). ZooplanktonZooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
, such as copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
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). Clupeids (Sardina pilchardus, the sardineSardine
Sardines, or pilchards, are several types of small, oily fish related to herrings, family Clupeidae. Sardines are named after the Mediterranean island of Sardinia, around which they were once abundant....
, and Sardinella aurita) were the most abundant. S. pilchards dominate in the cooler northern waters while S. aurita are dominate in warmer southern waters. Next most abundant were Jack mackerel (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 face two fates: They sink to the bottom or are consumed by zooplankton. If they settle to the bottom, phytoplankton release ammoniaAmmonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
during their decomposition
Decomposition
Decomposition is the process by which organic material is broken down into simpler forms of matter. The process is essential for recycling the finite matter that occupies physical space in the biome. Bodies of living organisms begin to decompose shortly after death...
, which returns nitrogen to the waters. Consequently, the phytoplankton remains could be consumed by benthic 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.
See also
- Christopher Columbus
- MadeiraMadeiraMadeira is a Portuguese archipelago that lies between and , just under 400 km north of Tenerife, Canary Islands, in the north Atlantic Ocean and an outermost region of the European Union...
- Elmina Castle
- Voyages of Christopher ColumbusVoyages of Christopher ColumbusIn the early modern period, the voyages of Columbus initiated European exploration and colonization of the American continents, and are thus of great significance in world history. Christopher Columbus was a navigator and an admiral for Castile, a country that later founded modern Spain...
- Eastern boundary current