Ocean currents
Published on 02 Feb 2025
Ocean currents are continuous, directed movements of seawater, driven by various factors, primarily wind, temperature, and the Earth's rotation.
Significance of ocean currents
Regulation of earth’s climate: By transferring heat from the equator to the poles.
Example: North Atlantic drift and Gulf Stream keeping North Sea warm which is unusual for such a high latitude.
Effect on local climate: Warm currents along the coast increases the temperature and cold current decreases the temperature.
Example: Cold Peruvian current moderating hot climate of Peru.
Economic: Fishing grounds, maintaining ports ice-free, navigation purposes etc.
Example: Cold Oyashio and warm Kuroshio meeting at Honshu Island making good fishing grounds; North Atlantic Drift keeping Murmansk port of Russia Ice-free etc.
Desert formation: Cold ocean currents along the continental margins make deserts.
Example: Humboldt current making Atacama Desert.
Rainfall: Warm ocean currents bring rainfall.
Example: North Atlantic Drift bringing rainfall on the western European coast.
Distribution of nutrients and heat: Through upwelling, thermohaline circulation etc.
Example: Great banks of New-Found land upwelling of nutrients.
Factors affecting ocean currents
Planetary winds: Frictional drag on the water surface exerted by the planetary winds moves surface waters
Example: North East trade winds driving north equatorial current.
Earth’s rotation: Moving water gets deflected by the influence of the Coriolis force.
Example: Circulation of Gulf Stream and Canary current clockwise in the northern hemisphere; West Wind Drift as a result of the rotation of earth from East to West.
Density and Salinity: Shallow surface currents of semi-enclosed water bodies are due to salinity differences
Example: Cooler, low-saline and low-density water from the Baltic Sea flow to the North Sea where warm high-saline and high-density water sinks.
Temperature difference: At high temperatures, ocean water expands in the equatorial region. This creates a slight gradient and water tends to flow down the slope.
Example: North Atlantic Drift moving from warm tropical waters of Mexico to cooler waters of the North Atlantic.
Pressure difference: Water moves from the areas of high-water level (low pressure) to low-water level areas (high-pressure belt).
Modifying factors: They do not help in the generation of ocean currents but they modify the existing ocean current.
Nature of sea coast: A land mass and diverts a current.
Example: The Atlantic Equatorial Current is bifurcated by the Cape of Sao Roque in Brazil to create the Cayenne Current and the Brazilian Current.
Ocean bottom relief: Underwater features such as sea mounts, MOR, can affect ocean current movements.
Example: Atlantic MOR affects the movements of North Atlantic Drift and North Atlantic Equatorial current.
Types of ocean currents
Based on location
Surface currents: Prevailing winds create surface currents. The wind imparts energy to the ocean surface, pushing water in the direction of the wind.
Example: Gulf stream driven by Westerlies
Thermohaline Circulation: Density differences caused by variations in temperature and salinity lead to deep, slow currents that circulate globally.
Example: Atlantic Meridional Overturning Circulation
Based on the temperature of the water
Warm current: Originates in the tropics and flows towards the poles with a temperature above the average temperature of the ocean.
Example: Kuroshio Current in the Pacific Ocean and Gulf Stream in the Atlantic Ocean
Cold currents: Originates from the polar region and flow towards the equator with a temperature below the average temperature of the ocean.
Example: California Current in the Pacific Ocean and Labrador Current in the Atlantic Ocean
Based on speed
Drift: Horizontal movement of water under the influence of wind. These are the slowest in speed.
Example: West wind drift, North Atlantic Drift.
Currents: Faster than drifts and flow in definite directions.
Example: Peru Current, Labrador Current etc.
Streams: It’s like the flow of a river flowing through the ocean in definite directions. These are the fastest.
Example: Gulf stream
Distribution of ocean currents
Lower and middle latitudes: Warm currents pass through the east of the continents in both hemispheres. Cold current passes through the west coast of the continents.
Example: Warm Kuroshio Current and Agulhas on the eastern coast of Asia and Africa respectively
Higher latitudes: Warm current through the west of the continents in the Northern Hemisphere and cold current passes through the east coast of the continents in the Northern Hemisphere.
Example: Warm Alaska current through the west coast and cold Labrador Current by the east coast of North America.