Ocean Currents – NDA Geography Notes

The oceans are not still. Vast streams of water, hundreds of kilometres wide and thousands of metres deep, move continuously through the world’s oceans, carrying heat from the tropics toward the poles and cold water from the poles back toward the tropics. These are ocean currents.

Ocean currents are one of the most important regulators of the Earth’s climate. The warm Gulf Stream keeps Western Europe far warmer than it would otherwise be at those latitudes. The cold Humboldt Current makes the west coast of Peru one of the world’s richest fishing grounds and also one of its driest coasts. El Niño: the periodic warming of the eastern Pacific: disrupts monsoons, causes droughts in some regions, and brings floods to others.

NDA tests this chapter very heavily, in three main forms: identifying whether a current is warm or cold, matching a current with its ocean or region, and understanding El Niño. This chapter requires precise factual recall. One wrong warm/cold classification can reverse an answer.

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What Causes Ocean Currents?

Wind is the most important driver of surface ocean currents. Persistent winds drag water along. Trade winds drive equatorial currents westward. Westerlies drive currents eastward in temperate latitudes.

Earth’s Rotation (Coriolis Effect) deflects currents, to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This creates the large circular current systems called gyres.

Differences in Water Density: denser water sinks; lighter water rises. Temperature and salinity differences drive deep ocean circulation.

Shape of Ocean Basins: continents and ocean floor features direct and deflect currents.

All four factors: Coriolis force, gravity (density differences), heating by solar energy, and wind: influence ocean currents. [NDA 2025-II]

Revolution of the Earth is NOT a factor. The gravitational pull of the Sun and Moon drives tides: NOT ocean currents.

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Ocean Gyres

A gyre is a large system of circular ocean currents forming a closed loop in an ocean basin. There are five major gyres: one in each ocean basin.

How a gyre works: Near the equator, trade winds push water westward (Equatorial Currents move west). This water reaches the western side and is deflected poleward. Westerlies push water eastward in mid-latitudes. This water is deflected equatorward along the eastern coast. The circle is closed.

The result of the Coriolis Effect:

• Northern Hemisphere: gyres rotate clockwise
• Southern Hemisphere: gyres rotate counter-clockwise

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Warm vs Cold Currents: The Pattern

Every ocean current is either warm or cold. A consistent pattern exists:

Warm currents flow from the tropics toward higher latitudes: on the western sides of ocean basins (which are the eastern sides of continents).

Cold currents flow from higher latitudes toward the tropics: on the eastern sides of ocean basins (which are the western sides of continents).

Coastline	Current Type	Example
Eastern coast of North America	Warm	Gulf Stream
Western coast of North America	Cold	California Current
Eastern coast of South America	Warm	Brazil Current
Western coast of South America	Cold	Peru/Humboldt Current
Eastern coast of Africa	Warm	Agulhas Current
Western coast of southern Africa	Cold	Benguela Current

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Major Currents: North Atlantic

Current	Type	Key Notes
Gulf Stream	WARM	Most powerful warm current in North Atlantic; from Gulf of Mexico northeast toward Europe
North Atlantic Drift	WARM	Extension of Gulf Stream; keeps NW Europe warm [NDA 2011-I]
Florida Current	WARM	Initial part of Gulf Stream, from Florida northward
Labrador Current	COLD	Flows south from Arctic along eastern Canada [NDA 2006-II]
Canary Current	COLD	Flows south along western Europe and North Africa

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Major Currents: South Atlantic

Current	Type	Key Notes
Brazil Current	WARM	Flows south along eastern coast of Brazil
Falkland (Malvinas) Current	COLD	Flows north along eastern coast of Argentina: NOT Chile [NDA 2006-II]
Benguela Current	COLD	Flows north along western coast of southern Africa [NDA 2024-II]
South Atlantic Drift	COLD	Flows eastward in southern Atlantic [NDA 2019-II]

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Major Currents: North Pacific

Current	Type	Key Notes
Kuroshio (Japan Current)	WARM	Pacific equivalent of Gulf Stream; flows northeast along Japan’s east coast [NDA 2014-II]
North Pacific Current	WARM	Extension of Kuroshio; crosses Pacific eastward
Alaska Current	WARM	Flows northwest along Alaskan coast [NDA 2025-I]
Oyashio (Kamchatka) Current	COLD	Flows south from Arctic along eastern Russia and Japan [NDA 2019-I]
California Current	COLD	Flows south along western USA coast

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Major Currents: South Pacific

Current	Type	Key Notes
East Australian Current	WARM	Flows south along eastern coast of Australia [NDA 2023-I]
Peru Current (Humboldt)	COLD	Flows north along western coast of South America [NDA 2011-II]
West Wind Drift	COLD	Flows eastward around Antarctica [NDA 2025-I]

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Major Currents: Indian Ocean

Current	Type	Key Notes
Agulhas Current	WARM	Flows south along eastern coast of Africa; Indian Ocean: NOT Pacific [NDA 2006-I]
Mozambique Current	WARM	Flows south through Mozambique Channel
West Australian Current	COLD	Flows north along western coast of Australia [NDA 2023-I]
Somali Current	Variable	Changes direction seasonally with the monsoon

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Effects of Ocean Currents on Climate

Warm currents moderate adjacent coastlines: raise temperatures in winter | increase moisture → more rainfall on windward coasts.

Cold currents cool and dry adjacent coastlines: lower temperatures even in tropics | stabilise the air (cold air cannot rise) → suppress rainfall → cause coastal deserts.

Gulf Stream and North Atlantic Drift

Western Europe (UK, France, Norway) is much warmer in winter than places at the same latitude in North America or Asia. The North Atlantic Drift carries warm water northeast from the Gulf of Mexico. Without it, London (51°N) would have winters as cold as Edmonton, Canada (~53°N). [NDA 2011-I]

NDA 2011-I key distinction: The UK, Norway, Netherlands, and Denmark are warmer because of the North Atlantic Drift: not simply because they are coastal. Being on the coast alone does not explain it. [NDA 2011-I]

Peru (Humboldt) Current and the Atacama Desert

The cold Peru Current flows northward along the west coast of South America. It chills the air above, making it stable and suppressing rainfall: creating the Atacama Desert, one of the driest places on Earth. It also creates one of the world’s richest fisheries because cold upwelling brings nutrients from the deep. [NDA 2011-II]

Benguela Current and the Namib Desert

The cold Benguela Current flows northward along the southwestern coast of Africa. It suppresses rainfall: creating the Namib Desert. The Benguela influences the west coast of South Africa (Namibia, South Africa): NOT North Africa. [NDA 2024-II]

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Fishing Grounds

Rich fishing grounds develop where cold and warm currents meet. The mixing stirs up nutrients from the deep and brings plankton to the surface.

Grand Banks: off Newfoundland, Canada. Cold Labrador Current meets warm Gulf Stream. One of the world’s most productive fisheries. [NDA 2009-I]

Dogger Bank: North Sea, off the coast of the United Kingdom. [NDA 2009-I]

In the absence of the cold Labrador Current, there would be no North-West Atlantic fishing grounds. The mixing of the two currents is the essential condition. Both: (1) Grand Banks is a major fishing ground; and (2) the meeting of Labrador and Gulf Stream creates ideal plankton conditions, are correct and (2) explains (1).

Fishing Ground	Location	PYQs
Grand Banks	Newfoundland Coast, Canada (Labrador + Gulf Stream)	[NDA 2009-I]
Dogger Bank	North Sea, off United Kingdom	[NDA 2009-I]

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El Niño and La Niña

Normal Pacific Conditions

Trade winds blow strongly from east to west across the Pacific. They push warm surface water toward the western Pacific (Australia, Indonesia, Philippines). The western Pacific gets heavy rainfall. Cold upwelling occurs in the eastern Pacific off Peru, making it cold and dry but extremely productive for fishing.

El Niño

The trade winds weaken. The warm water spread eastward. The eastern Pacific becomes unusually warm off Peru, bringing heavy rainfall to usually dry Peru/Ecuador. The western Pacific loses warm water. Australia, Indonesia, and India get less rainfall → drought.

El Niño appears along the coast of Peru. [NDA 2008-I]

Three confirmed effects of El Niño: [NDA 2013-II]

1. Reduction in plankton as the sea surface becomes warm, meaning fewer fish off Peru.
2. Irregularities in the evaporation of seawater.
3. Distortion of equatorial atmospheric circulation (Walker Circulation). : All three are correct. [NDA 2013-II]

Two confirmed characteristics of El Niño: [NDA 2010-II]

El Niño occurs at irregular intervals (roughly every 2–7 years) | El Niño carries warmer water (than normal off Peru) . Both correct. [NDA 2010-II]

Flow of southeast trade winds toward the Indian Ocean is NOT a result of El Niño. During El Niño, the trade winds weaken rather than strengthen.

La Niña

La Niña is the opposite of El Niño, with stronger-than-normal trade winds. La Niña brings above-normal monsoon rainfall in India | above-normal rainfall in Australia | drought in Peru.

Event	Trade Winds	India/Australia	Peru/Ecuador	Fishing off Peru
Normal	Strong (east to west)	Wet	Dry but productive	Excellent
El Niño	Weakened	Drought	Floods	Collapsed
La Niña	Stronger than normal	Above-normal rain	Drought	Excellent

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