What is Ocean Current? It is a horizontal movement of seawater that is produced by gravity, wind, and water density. Ocean currents play an important role in the determination of climates of coastal regions.

As an important topic of Geography (Oceanography), questions could be framed either in Prelims or Mains (GS 1) papers of the IAS Exam.

Candidates can check previous years’ Geography Questions in UPSC Prelims in the linked article.

Understand the basics of ocean currents in this article.

Ocean Water and Ocean Currents

The movement of ocean water is continuous. This movement of ocean water is broadly categorized into three types:

• Waves
• Tides
• Currents

The streams of water that flow constantly on the ocean surface in definite directions are called ocean currents.

Ocean currents are one of the factors that affect the temperature of ocean water.

• Warm ocean currents raise the temperature in cold areas
• Cold ocean currents decrease the temperature in warmer areas.

To understand the ocean waves and related concepts, check the links below:

Relevant Facts about Ocean Currents for UPSC

1. The magnitude of the ocean currents ranges from a few centimetres per second to as much as 4 metres (about 13 feet) per second.
2. The intensity of the ocean currents generally decreases with increasing depth.
3. The speed of ocean currents is more than that of upwelling or downwelling which are the vertical movements of ocean water.
4. There are two types of ocean currents:
   • Warm Ocean Currents
   • Cold Ocean Currents

What causes ocean currents?

Horizontal pressure-gradient forces, Coriolis forces, and frictional forces are important forces that cause and affect ocean currents. NCERT Notes on Factors Affecting Wind mention Coriolis Force that one can read in the linked article.

Rise and fall of the tide

Tides give rise to tidal currents. Near the shore, tidal currents are the strongest. The change in tidal currents is periodical in nature and can be predicted for the near future. The speed of tidal currents at some places can be around 8 knots or more.

Wind

The ocean currents at or near the ocean surface are driven by wind forces.

Thermohaline Circulation

‘Thermo’ stands for temperature and ‘Haline’ stands for salinity. The variations in temperature and salinity at different parts of the oceans create density differences which in turn affect the ocean currents.

What is a Frictional Force?

The movement of water through the oceans is slowed by friction, with surrounding fluid moving at a different velocity. A faster-moving layer of water and a slower-moving layer of water would impact each other. This causes momentum transfer between both layers producing frictional forces.

What are geostrophic currents?

When the pressure gradient force on the ocean current is balanced by the Coriolis forces, it results in the geostrophic currents.

• The direction of geostrophic flow is parallel to an isobar.
• The high pressure is to the right of the flow in the Northern Hemisphere, and the high pressure to the left is found in the Southern Hemisphere.

North and South Equatorial Currents

North Equatorial Current

• North Equatorial Current flows from east to west in the Pacific and the Atlantic Ocean.
• North Equatorial Current flows between the latitudes of 10 degrees and 20 degrees north.
• It is not connected to the equator.
• Equatorial circulation separates this current between the Pacific and Atlantic oceans.

South Equatorial Current

• It flows in the Pacific, Atlantic, and Indian oceans.
• The direction of the south equatorial current is east to west.
• The latitudes in which the current flows are between the equator and 20 degrees south.
• It flows across the equator to 5 degrees north latitudes in the Pacific and Atlantic Oceans.

What is the Equatorial Counter Current?

It is found in the following three oceans:

• Indian Ocean
• Atlantic Ocean
• Pacific Ocean

It is found between north and south equatorial currents at about 3-10 degrees north latitude.

What is Antarctic Circumpolar Current?

The ocean current that flows clockwise around the Antarctic is called the Antarctic Circumpolar Current. It is also called West Wind Drift. It is a feature of ocean circulation of the Southern Ocean.

• It does not have a well-defined axis
• It consists of a series of individual currents which are separated by frontal zones.

What is a Global Conveyor Belt?

A system of ocean currents that helps in the transportation of water around the world is called a global conveyor belt. As per National Geographic, “Along this conveyor belt, heat and nutrients are moved around the world in a leisurely 1000-year cycle.”

Distribution of Ocean Currents

The ocean currents are distributed across five oceans. The list of important ocean-wise currents is given below:

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