Maarg Manthan · Topic 11.4

Effects of Ocean Currents

Geography › Ocean Movements, Temperature and Salinity · Topic 11.4

Ocean currents change the temperature and rainfall of the coasts they touch, create fog and deserts, bring plankton and fish to the great fishing grounds where warm and cold currents meet, carry icebergs and affect navigation, and spread marine pollution. They also help to control the Earth's heat budget, moving warm water poleward and cold water toward the equator.

6 min read · UPSC Prelims · Geography · Ocean Movements, Temperature and Salinity

At a Glance

Climate Warm currents warm and moisten; cold currents cool and dry
Fisheries Warm-cold meeting zones
Navigation Icebergs, fog and fuel saving
Deserts Atacama, Namib
Pollution Garbage patches and oil spills
Exam link UPSC Prelims, Geography: Ocean Movements, Temperature and Salinity

Where Does It Fit?

This is the fourth topic of the category on ocean movements, temperature and salinity. The previous topics described the causes and the regional patterns of currents, and this one explains what the currents do to climate, life and trade. The next topic begins the study of tides. Previous topic: Indian Ocean Currents. Next topic: Tides and Their Types.

How Do Ocean Currents Affect Climate?

In short: a warm current warms and wets the air above it, and a cold current cools and dries it.

Effect	Mechanism	Examples
Warmer coasts in high latitudes	Warm currents carry heat poleward and warm the winds that blow over them	The Gulf Stream and North Atlantic Drift keep northwestern Europe and the ports of Norway ice-free in winter; the Alaska Current warms the coast of Alaska; Britain is much warmer than Labrador at the same latitude
Cooler tropical coasts	Cold currents cool the air along western coasts	Peru, Benguela and Canary currents lower coastal temperatures; Lima and Walvis Bay are cooler than other places at the same latitude
Rainfall	Warm currents increase evaporation, humidity and rain on the east coasts; cold currents stabilise the air and prevent rain	Rain along the east coasts of Brazil, Florida and Japan; the dry coasts of Atacama, Namib and Baja California
Deserts	Cold currents and onshore winds give fog but no rain	The Atacama, Namib and the coastal Sahara; the Atacama is among the driest places on Earth
Fog	Warm moist air cooled by a cold current to its dew point	Fog at the Grand Banks where the Gulf Stream meets the Labrador Current; the summer fog of San Francisco over the California Current; the fogs of the Kuril coast, as in Clouds, Fog and Forms of Condensation
Cyclones and monsoon	Warm seas feed tropical cyclones; ocean heat influences monsoon rain	Typhoons over the Kuroshio region; the heat in the Arabian Sea and Bay of Bengal, as in Tropical Cyclones – Formation and Conditions

Currents also drive climate cycles. The weakening of the Peru Current in El Niño changes weather across the world, as in El Niño and Its Effects, and the large-scale circulation moves a major share of the heat from the equator to the poles, along with the atmosphere, as in Heat Transfer and Heat Budget of the Earth.

How Do Currents Affect Fishing and Marine Life?

Plankton and food chains: where a warm and a cold current meet, or where deep cold water comes to the surface by upwelling, nutrients reach the sunlit layer and plankton bloom. This is the base of the food chain.
Major fishing grounds: the Grand Banks (Gulf Stream and Labrador), the seas around Japan (Kuroshio and Oyashio), the Peruvian coast (Peru Current), the North Sea, the coast of Namibia and South Africa (Benguela) and the Somali-Arabian coast (summer upwelling) are the world’s best fishing grounds, as in Marginal Seas.
Larval and species dispersal: currents transport the eggs and larvae of fish, corals and eels over long distances, such as the eels of the Sargasso Sea, which cross the Atlantic with the Gulf Stream.
Warm-water intrusions: in El Niño years, the Peruvian anchovy collapses as the cold, rich upwelling is replaced by warm water. The marine heatwaves are now affecting the distribution of fish stocks, and fishing communities, including those of India, are seeing the shift of the catch.

Ships use currents to save time and fuel, sailing with the Gulf Stream and avoiding the Labrador Current when going the other way. The cold Labrador Current carries icebergs from Greenland into the shipping lanes of the North Atlantic, and the combination of icebergs and fog near the Grand Banks led to the sinking of the Titanic in 1912, after which the International Ice Patrol was set up. Warm currents keep high-latitude ports ice-free, such as Murmansk in Russia, which has open water year-round because of the North Atlantic Drift. Ancient sailors used the monsoon drift for trade across the Indian Ocean, as in Indian Ocean Currents.

Currents also carry marine pollution. Plastic and other floating wastes are swept into the centres of the gyres, forming huge garbage patches, such as the Great Pacific Garbage Patch, and oil spills from tankers spread with the currents. As an analytical point, the same currents that enrich fisheries and soften the climate also move the contaminants, so the management of the ocean needs to be international, and the United Nations negotiations on a global plastics treaty are an attempt to do this.

Why Is This Topic Important?

Application Climate and fish questions
Examples Named regions
Environment Marine pollution

What Came Next?

The next topic begins the study of tides, the rhythmic rise and fall of the sea. Next topic: Tides and Their Types.

Key People and Terms

Upwelling Rise of cold nutrient-rich water
Plankton Tiny drifting organisms
Iceberg Floating mass of glacier ice
Garbage patch Concentration of floating waste in a gyre
Marine heatwave Prolonged unusually warm sea
International Ice Patrol Iceberg watch set up after the Titanic

Exam Corner

Points to Remember

Warm currents warm and wet; cold currents cool and dry.
Meeting of warm and cold gives fish and fog.
Labrador carries icebergs.
Atacama and Namib are current-made deserts.
Plastic collects in gyres.

Do Not Confuse With

Upwelling and downwelling Rising versus sinking water
Fog from cold current and radiation fog Air cooled by the sea versus the ground
Warm current effect and cold current effect Rain versus aridity

Memory Hook

Warm brings rain and open ports, cold brings fog and deserts; where they meet, the fish and the icebergs.

Mains Angle

Questions ask for effects with examples. These points add depth.

Climate Heat redistribution
Economy Fisheries and shipping
Risk Pollution and heatwaves

A Question You May Face

An original practice question, not a past paper question.

“Discuss the effects of ocean currents on the climate, fisheries and navigation of the regions they flow through.”

How to Answer

Climate Warm and cold coasts.
Fish Upwelling and meeting zones.
Navigation Icebergs and fog.
Risks Pollution and warming.

GS Relevance

Prelims and Mains: effects of warm and cold currents on climate, fisheries and shipping with examples. GS Paper 1: oceanography; GS Paper 3: marine pollution.

Frequently Asked Questions

How do ocean currents affect climate?

Warm currents carry heat to higher latitudes and warm and moisten the air over coasts, as the Gulf Stream does for northwestern Europe. Cold currents cool the coasts, stabilise the air and cause dry or foggy conditions, as the Peru and Benguela currents do for the Atacama and the Namib.

Why are warm and cold current meeting points good fishing grounds?

Where warm and cold currents meet, the mixing of waters brings up nutrients and supports a bloom of plankton, the base of the food chain. This attracts large numbers of fish. The Grand Banks and the sea off Japan are famous examples.

How do cold currents lead to the formation of deserts?

A cold current cools the air above it, making it stable and dense, so that moisture does not rise and condense to form clouds and rain. The coastal air carries fog but not rain, and the land behind becomes arid, as in the Atacama and the Namib deserts.

How do ocean currents affect navigation?

Ships use favourable currents such as the Gulf Stream to save fuel and time, and warm currents keep ports free from ice. Cold currents such as the Labrador carry icebergs and bring fog into shipping lanes, which is the reason for the Titanic disaster in 1912.

How do ocean currents spread marine pollution?

Currents carry floating plastics, oil and other pollutants across oceans and concentrate them in the calm centres of the gyres, forming garbage patches such as the Great Pacific Garbage Patch. Oil spills from tankers also spread with the currents, harming coasts far from the source.

PYQ Practice — Statement Analysis

1 The North Atlantic Drift keeps the ports of northern Norway ice-free in winter.

True

It carries warm water north.

2 Cold currents generally increase rainfall on the coast.

False

They make the air stable and dry.

3 The Grand Banks fishery lies where the Gulf Stream meets the Labrador Current.