The Canary Current is a cold, slow, southward-flowing current that runs along the Atlantic coast of northwest Africa, from off Portugal and Spain past Morocco, Western Sahara and Mauritania before turning west near Senegal to join the North Equatorial Current. It is the eastern boundary current of the North Atlantic subtropical gyre — the return arm of the loop whose western side is the Gulf Stream — and like all eastern boundary currents it is broad, sluggish and shallow rather than narrow and fast. Its defining feature is upwelling: winds blowing from the north along a north-south coast drive surface water offshore, and cold, nutrient-rich water rises to replace it. That makes the Canary system one of the four great eastern boundary upwelling regions of the world ocean, supporting one of the largest fisheries in the Atlantic. It also makes the sea off the Sahara far colder than its latitude suggests, which is why the eastern Canary Islands are near-desert and why sea temperatures off Morocco in summer are closer to those off Cornwall than those off Florida.
The Return Arm of the Gyre
Subtropical ocean gyres are closed loops, and their two sides look nothing alike. On the western side of the North Atlantic, all the flow is concentrated into the fast, deep, warm Gulf Stream. On the eastern side, the return flow is spread across hundreds of kilometres of ocean, moving at a few centimetres per second — slow enough that a drifting object takes months to make progress a Gulf Stream ring would cover in days.
The current is fed by water arriving from the north — some of it the tail of the North Atlantic Drift after it has swung south past Iberia — and it is cool because it comes from higher latitudes and because upwelling keeps refreshing it from below. It runs south past the Canary Islands, which sit directly in it and give it its name, and continues to about the latitude of Dakar before the trade winds turn it west across the Atlantic.
That westward turn is why the Canary Current matters to the history of transatlantic navigation, and it is the reason the Canaries became the standard departure point for voyages to the Americas.
Upwelling Along the Saharan Shelf
The upwelling here works on the same principle as the Humboldt's, mirrored for the Northern Hemisphere. Trade winds blow from the northeast along a coast running roughly north-south; Coriolis deflection in the Northern Hemisphere pushes wind-driven surface water to the right of the wind, which on this coast means offshore; and cold, nutrient-rich water rises from a few hundred metres to replace it.
The intensity varies along the coast because the winds do. Off Morocco and northern Western Sahara, upwelling is seasonal, strongest in spring and summer when the Azores high is well established. Off Cap Blanc, on the Mauritanian border, it is essentially permanent, because the trade winds blow there year-round. That permanent cell is the productive heart of the system, and the transition zone around Cap Blanc — where the cool, upwelled northern water meets warmer tropical water from the south — is one of the sharpest ecological boundaries in the Atlantic.
The upwelled water supports blooms of phytoplankton, which support sardine, sardinella, anchovy, mackerel and horse mackerel, which support a fishery that lands well over a million tonnes a year. The same physics operates on the other three great upwelling coasts — the Humboldt off Peru, the Benguela off Namibia, and the California Current — all of them cold water on the west-facing side of a subtropical landmass.
A Fishery Several Countries Argue Over
Rich fish stocks off a politically contested coastline have produced decades of dispute.
The stocks are shared and migratory: small pelagic fish move along the coast across the waters of Morocco, Western Sahara, Mauritania, Senegal, Guinea-Bissau and the Gambia, which makes unilateral management close to meaningless and cooperative management difficult. Distant-water fleets from Europe, Russia, China, Japan and Korea have fished the region heavily since the 1960s, and access agreements with coastal states have been a persistent source of friction over price, monitoring and enforcement.
The sharpest issue is Western Sahara. Its status is disputed, and fisheries agreements negotiated between the European Union and Morocco that extend to waters off Western Sahara have been repeatedly challenged in the European courts on the grounds that they dispose of the resources of a territory whose people have not consented. Rulings have gone against elements of those agreements more than once, and the arrangements have been renegotiated and challenged again. It is one of the few places where the law of self-determination is argued largely through fishing quotas.
There is also an ecological complication with a familiar shape: the octopus and sardinella stocks of the region have shown the boom-and-collapse behaviour typical of upwelling fisheries, amplified by the fact that upwelling strength itself varies from year to year.
Dust Falling on Cold Water
This is the one upwelling system that sits directly downwind of a desert, and the combination produces something the others do not have.
The Sahara is the largest dust source on Earth, and a great deal of what it lifts blows west out over exactly this stretch of ocean. Satellite images of the coast between Morocco and Mauritania regularly show ochre plumes streaming hundreds of kilometres offshore, sometimes engulfing the Canary Islands entirely in the event Spanish forecasters call a calima.
What lands in the sea is fertiliser. Saharan dust carries iron and phosphorus, and while the Canary system already has plenty of nutrients from upwelling, the dust supplies iron in a region where the open ocean further offshore is short of it. The deposition helps sustain productivity beyond the narrow upwelling strip, and it is part of the same continental-scale dust system that fertilises the Amazon after crossing the whole Atlantic.
The dust has a second, less welcome role. It carries microorganisms and, on the islands themselves, calima events drive air quality sharply down and periodically close Canary airports. The physical geography joins up neatly: the same trade winds that drive the upwelling drive the dust, and the same latitude band that makes the Sahara a desert makes the ocean beside it cold.
The result of all this is a stretch of sea that behaves as though it belongs a thousand kilometres further north. Summer sea surface temperatures off the Western Sahara coast sit in the high teens, cold enough that reef-building coral cannot establish at a latitude where it otherwise would, and cold-water species turn up well inside the tropics. Divers in the Canaries find a fauna with far more in common with the Mediterranean and the Azores than with Cape Verde a few hundred kilometres south, which sits in warm tropical water on the other side of the current's turn.
Why Lanzarote Is Drier Than La Palma
The Canary Islands are strung across about 450 km of ocean at essentially the same latitude, and yet the eastern islands are near-desert while the western ones are green. Two effects combine.
The first is the current. Cold water cools the air above it and produces a strong, low temperature inversion — the trade wind inversion — which caps vertical motion and prevents convective rainfall. Air is held in a moist, cool layer near the surface, forming persistent low cloud rather than rain. This is the same mechanism that produces the Atacama and the Namib.
The second is topography. Where an island rises high enough to force that moist layer upward, it wrings the water out. La Palma, Tenerife and La Gomera all reach well above the inversion, and their northern slopes carry laurel forest — relict subtropical woodland fed by cloud stripped from the trade winds by the vegetation itself. Lanzarote and Fuerteventura are low, flat and old, do not reach the inversion, and receive almost nothing: annual rainfall on Fuerteventura is comparable to parts of the Sahara it faces. The islands' wider geography is covered in the Canary Islands guide.
The Current That Carried Columbus
The Canary Current and the trade winds above it form the outbound half of the sailing route that connected Europe to the Americas, and the pairing was worked out before anyone knew America was there.
Portuguese navigators exploring down the African coast in the fifteenth century discovered a problem: sailing south with the wind and current behind them was easy, and sailing home against both was close to impossible. The solution, the volta do mar, was to stand far out into the Atlantic on the return, sail north until reaching the belt of westerlies, and then run east to Europe. It required trusting open water out of sight of land, and it was the single most important navigational advance of the period.
Columbus, who had lived in Madeira and sailed the African coast, applied the same logic westward. He departed from La Gomera in the Canaries rather than from Spain precisely because that put him in the trade winds and the current, and he returned on a northern track through the westerlies. The route he used became the standard: the outbound leg down to the Canaries and across with the trades, the return leg north via the Azores. For four centuries, the shape of Atlantic empire followed the shape of this gyre.