Currents of the Atlantic Ocean

Detail

Basic ideas first

• Ocean current: a large, steady flow of seawater in one direction, like a river inside the ocean.
• Warm current: flows from low latitudes (near the equator) towards the poles. It warms the coasts it passes.
• Cold current: flows from high latitudes (near the poles) towards the equator. It cools the coasts it passes.
• Gyre: a large ring of currents that goes round an ocean basin.
• Clockwise in the Northern Hemisphere (North Atlantic).
• Anticlockwise in the Southern Hemisphere (South Atlantic).

• This happens because of the Coriolis force (the turning effect of the earth's rotation, which pushes moving water to the right in the Northern Hemisphere and to the left in the Southern Hemisphere) and the planetary winds.

• General rule for the Atlantic:

• Western side of each basin (the Americas): warm currents (Gulf Stream, Brazil).
• Eastern side (Europe and Africa): cold currents (Canary, Benguela).
• Exception: the North Atlantic Drift brings warm water to the eastern side at high latitudes (north-west Europe).

North Atlantic gyre (clockwise)

Gulf Stream (warm)

• Course:
• It leaves the Gulf of Mexico through the Florida Strait (between Florida and Cuba, about 24°N).
• It runs north along the US east coast.

• It passes Cape Hatteras (North Carolina, about 35°N), then turns north-east and flows out to sea towards Newfoundland (Canada).

• It is one of the strongest warm currents in the world.

• Average speed: about 6.4 km per hour [2].
• Fastest near the surface, usually up to about 9 km per hour [2].

• It widens and slows to about 1.6 km per hour further north [2].

• It carries more water than all the world's rivers put together [2].

North Atlantic Drift (warm)

• Definition: the Gulf Stream's continuation east and north-east across the Atlantic towards north-west Europe. The westerly winds drive it, so it is called a "drift": a slow, wind-driven surface flow.
• Effects on north-west Europe:
• Mild winters: Britain and Norway are much warmer than other places at the same latitude, such as Labrador in Canada.
• Ice-free ports: Norwegian ports such as Hammerfest (about 70°N) and Narvik, and Murmansk in Russia (on the Kola Peninsula), stay open all winter, even north of the Arctic Circle.
• Isotherms bend north: isotherms (lines on a map joining places with the same temperature) curve towards the pole over the north-east Atlantic, because the water there is warmer than usual for that latitude.

• Higher North Sea salinity: salty water from the tropics flows into the North Sea. (Salinity is the amount of dissolved salt in seawater.)

• Why the winters are mild, step by step:

• Warm tropical water flows to high latitudes.
• The westerly winds blow over this warm water and pick up heat and moisture.
• The winds carry the heat onto land, so winters are mild and wet, and the sea does not freeze.

Canary Current (cold)

• Course: flows south along north-west Africa, from Spain (Iberian coast) to Senegal.
• Effects:
• Coastal Saharan dryness: cold water cools the air above it. Cool air holds little moisture and does not rise, so little rain falls on the Atlantic coast of the Sahara.
• Upwelling fisheries: upwelling is cold, nutrient-rich water rising from the deep sea to the surface. The nutrients feed plankton (tiny floating plants and animals), and plankton feed fish. So the coasts of Morocco, Western Sahara, Mauritania and Senegal have rich fishing grounds.

North Equatorial Current (warm)

• The trade winds drive it from east to west across the tropical Atlantic.
• It brings water back to the Caribbean and the Gulf of Mexico, which completes the clockwise loop.

The Sargasso Sea

• Definition: a calm, warm area of the North Atlantic (roughly east of Bermuda). It has no land boundary.
• It is the only sea with no land boundary. Only ocean currents mark its edges [3].

• The currents around it are the Gulf Stream (west), the North Atlantic Drift (north), the Canary Current (east) and the North Equatorial Current (south).

• Why it is calm: it sits at the centre of the clockwise gyre. Water collects there and moves slowly, so there is little mixing.

• Sargassum: floating brown seaweed covers the surface.
• It is a brown alga (a simple, plant-like sea organism). It forms a floating ecosystem on the open ocean that produces a lot of food [3].

• The Sargasso species are holopelagic (they spend their whole life floating in the open ocean). They grow and reproduce on the high seas without ever attaching to the sea floor [3].

• Breeding ground (beyond NCERT):

• European and American eels migrate there to spawn (lay eggs). Their young drift back to Europe and North America on the currents.
• It is a spawning ground for endangered anguillid eels (the freshwater eel family), and also for white marlin, porbeagle shark and dolphinfish [4].

Labrador Current and the subpolar loop

Labrador Current (cold)

• Course: flows south from the Arctic (Baffin Bay and Davis Strait), past Labrador and Newfoundland (Canada).
• Effects:
• Cold climate: it lowers temperatures in north-east North America. Labrador's ports freeze in winter, while Norwegian ports at higher latitudes stay open.

• Icebergs: it carries icebergs that have broken off Greenland's glaciers into the shipping lanes. In April 1912, the Titanic sank after hitting one of these icebergs south of Newfoundland.

• Meeting with the Gulf Stream off Newfoundland, step by step:

• Dense fog: warm, moist air over the Gulf Stream moves over the cold Labrador water. The air cools, its water vapour condenses, and thick fog forms. This is a major danger to ships.
• Grand Banks fishery: the Grand Banks are shallow parts of the continental shelf off Newfoundland. Warm and cold water mix there and nutrients spread through the water. Plankton grow well, so fish are plentiful. It is one of the world's great fishing grounds (cod).

Subpolar loop (beyond NCERT)

• East Greenland Current (cold): flows south along Greenland's east coast and carries Arctic water and ice.
• Irminger Current (warm): a branch of the North Atlantic Drift that flows west past south and west Iceland.
• Together with the Labrador Current and the North Atlantic Drift, they form a smaller anticlockwise loop north of the main gyre.

South Atlantic gyre (anticlockwise)

Brazil Current (warm)

• Course: the South Equatorial Current splits at Cabo de São Roque (the eastern tip of Brazil). The southern branch flows south along Brazil as the Brazil Current.

Falkland Current (cold)

• Course: flows north along Argentina. It is a branch of the West Wind Drift (Antarctic Circumpolar Current: the cold current driven east around Antarctica by the westerly winds).
• Confluence: it meets the warm Brazil Current off the Río de la Plata estuary (Argentina and Uruguay, about 35°S). Warm and cold water mix there, which helps fishing.

Benguela Current (cold)

• Course: flows north along south-west Africa (South Africa, Namibia, Angola). It reaches almost to the Equator [5].
• Upwelling, step by step:
• Winds from the south and south-west blow along the coast and push surface water away from the shore [5].
• Cool, slightly less salty water full of plankton rises from below [5].

• Result: rich fisheries off Namibia and South Africa.

• Namib, a foggy coastal desert:

• The cold water cools the air above it, so the air cannot hold much moisture. Very little rain falls, so the coast is dry [6].
• The cold water also cools the moisture that is already in the air. It condenses into fog, which often drifts onto the coast. So the Namib is a desert with fairly high humidity [6].

Guinea Current (warm; beyond NCERT)

• A warm current that flows eastward in the Gulf of Guinea along the West African coast (Côte d'Ivoire to Nigeria).

Comparison table

Current	Type	Direction	Coast	Main effect
Gulf Stream	Warm	North, then north-east	US east coast (Florida → Cape Hatteras → Newfoundland)	Moves heat towards the pole; fog off Newfoundland
North Atlantic Drift	Warm	North-east	Britain, Norway	Mild winters, ice-free ports, isotherms bend north
Canary	Cold	South	Spain → Senegal	Dry coastal Sahara; upwelling fisheries
North Equatorial	Warm	West	Tropical Atlantic	Completes the North Atlantic gyre
Labrador	Cold	South	Labrador, Newfoundland	Icebergs, cold climate, Grand Banks
Brazil	Warm	South	Brazil	Branch of the South Equatorial Current
Falkland	Cold	North	Argentina	Meets the Brazil Current off the Río de la Plata
Benguela	Cold	North	Namibia, South Africa	Foggy Namib desert; upwelling fisheries
Guinea	Warm	East	Gulf of Guinea	Equatorial counter-flow

Prelims Hooks

• The Sargasso Sea is the only sea with no land boundary. Currents enclose it: Gulf Stream, North Atlantic Drift, Canary and North Equatorial.
• The Gulf Stream leaves the Gulf of Mexico through the Florida Strait and turns away from the US coast at Cape Hatteras.
• Hammerfest, Narvik and Murmansk stay ice-free because of the North Atlantic Drift, not the Gulf Stream itself.
• Grand Banks (Newfoundland): the warm Gulf Stream meets the cold Labrador Current. Result: fog and a rich fishery.
• The Falkland Current (cold) meets the Brazil Current (warm) off the Río de la Plata.
• Canary → coastal Sahara and Benguela → Namib: cold currents make west-coast deserts drier. The Benguela also makes the Namib foggy.
• Trap: the Benguela and Canary currents are cold, while the Brazil and Guinea currents are warm. All the Atlantic cold currents named here flow towards the equator, except that the Falkland flows north from the Southern Ocean.
• West to east across the North Atlantic: Gulf Stream → North Atlantic Drift → Canary Current.
• Sargassum is a holopelagic brown alga. The Sargasso Sea is the spawning ground of European and American eels.

Mains Points

• Currents shape climate on western and eastern coasts:
• Warm currents on the western side of basins (Gulf Stream, Brazil) bring heat and moisture.
• Cold currents on the eastern side (Canary, Benguela) help create coastal deserts such as the Sahara coast and the Namib.

• The North Atlantic Drift breaks this pattern. It gives north-west Europe mild winters and ice-free ports even north of the Arctic Circle.

• Fisheries and the economy:

• Upwelling zones (Canary, Benguela) and meeting zones of warm and cold water (Grand Banks, Río de la Plata) are rich in plankton, so they support some of the world's richest fishing grounds.

• These grounds are at risk from overfishing (for example, the cod collapse on the Grand Banks) and from ocean warming. This links to GS-III themes of resources and environment.

• Hazards to shipping:

• The Labrador Current carries icebergs into transatlantic sea routes (the Titanic, 1912).
• Where warm and cold currents meet, dense fog forms.

• These dangers show why ocean monitoring matters. India's INCOIS plays a similar role for the Indian Ocean.

• Biodiversity of the high seas:

• The Sargasso Sea has no land boundary, so it lies outside any country's control.
• It supports endangered eels and floating sargassum ecosystems. This shows why the world needs an agreement to protect life on the high seas.