12 Mar 2016

Ocean Currents Facts, Causes and Importnace

ocean currents

There are regular flows of sea and ocean waters from one direction to another. These streams of water are known as ocean currents. Such a current can be horizontal or vertical. They can be observed on the surface level or deep inside the oceans.

Ocean currents are like huge rivers of the oceans. Some of these are very big in length and wide in breadth. Others are not so big and also limited in geographical extent.

There are many factors which combine to generate these currents. Major roles are played by the winds, distribution of global temperature, difference of salinity, gravity and rotation of the earth.

Ocean currents are one of the most important factors that affect the climate of various regions. The temperature and rainfall in places which are near the coast line of major seas and oceans can be influenced by the nearby ocean currents.

Causes of Ocean Currents

Wind flow is one of the most important factors behind origin of ocean currents. Due to the existence of many permanent or semi permanent pressure belts there are regular flows of wind to a specific direction. The wind when flows over the ocean surface create friction upon the water which forces it to move along the path of the wind-flow.

Difference of temperature in various areas of the earth due to the variation of intensity of sunlight in different latitudes is another major cause of ocean currents. Temperature moves water and thus creates a flow. Hot water is lighter than the cold water, it sometimes create upward or downward movement of water.

We know that seawater is saline. But the amount of salinity is not same everywhere. Big rivers can alter the salinity of the seas near its estuary by carrying tons of fresh water. Some regions of the oceans receive a lot of rainfall where in many areas rainfall is scarce. It also results in disparity of salinity. The difference of salinity creates currents of sea waters.

The earth is not flat. It is a round shaped planet and so the surface level of the oceans is not even in all areas. The surface level of the ocean water around the equator is in much higher position than the water near the poles. So, gravity plays a major role here by pulling the water from the higher regions to lower regions. The gravitational pull of sun and moon is also a factor behind the currents.

Earth rotates around its own axis. The speed of that movement is highest near the equator and lowest near the polls. That rotation results in centrifugal force which moves the waters around the globe.

The rotation of the earth is also the reason behind Coriolis Effect. Due to it the ocean current rotates clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere.

Types of Ocean Currents

We can group the currents as surface level and sub-surface currents. The surface level currents are visible but the sub-surface level currents remain hidden. The deep currents flow in a depth more than 400 meters.
The subsurface currents are also known as thermohaline circulation. Gravity is a major driving force behind these currents which are slower in speed. The difference between salinity and temperature between the surface and deep seas are also important reason behind thermohaline circulations.

The surface level ocean currents are also classified in two groups – cold and Warm currents. Cold and warm are relative terms here. The cold current is much cooler than the water around the reason and exactly opposite in the case of warm currents.


The Ocean currents never flows strait due to the Coriolis Effect. Sometimes, opposite moving currents circulates around a region of ocean. That region is bounded by different streams is called a Gyre. It is a part of an ocean where relatively calm water is surrounded by fast moving currents.

Saragossa Sea is a fine example of Gyre in the North Atlantic Ocean. All three major oceans have gyres. Atlantic has two,Pacific Ocean has another two and the Indian Ocean has only one. The circulating ocean streams tend to accumulate ocean debris, jellyfishes and seaweeds inside these big oceanic lakes.

Impact of Ocean Currents in Weather

The ocean currents influence the weather around the coastal regions. Warm currents keep the regions of colder latitude relatively warm. As for example, warm Gulf Stream which brings the water from the equatorial zones to the temperate zones of Western Europe keeps those areas warmer than its normal level. The opposite effects can be seen in the coasts that are near the cold streams.

Ocean Currents are also responsible for movement of moisture. The temperature difference cause by the ocean currents create mists and clouds and sometimes result in rain or snow falls around the globe.

Major Ocean Currents

There are many large and long ocean currents in the five oceans and adjoining seas of the world. Some of the important currents in the Arctic Ocean are East Greenland Current and Norwegian Current. Southern Ocean has Antarctic Circumpolar Current.

Ocean Surface Currents Map
Ocean Surface Currents Map [ Image Credit: NOAA ]
Major warm currents of the Atlantic Ocean are Gulf Stream, North Atlantic Drift, Brazil Current, Canaries Current,  Benguela Current etc. Cool Atlantic currents are Canaries Current, Labrador Current etc.

Pacific Ocean has also many very large currents both warm and cool. Alaska Current, Kuroshio (Japan) Current, North Pacific Drift, East Australian Current, California Current etc are examples of long warm currents. Important cooler variations are Oyashio (Kamchatka) Current, West Wind Drift, and Humboldt (Peru) Current etc.

West Australian Current is a cool stream which is in the Indian Ocean. Agulhas Current is an example of a warm current in the same ocean.

Importance of Ocean Currents

Ocean currents do not only impact the weather patterns around the globe. They have historical importance in global commerce and colonization. During the age of sails the ships tend to follow the course of the current streams to cross the vast oceans. Even today, the modern ships keep track of the currents to avoid icebergs and extra fuel costs.

The currents move the ocean debris from the coasts to the inside of the oceans. They accumulate these oceans in areas between the two opposite flowing currents, known as gyres. The Great Pacific Garbage Patch and North Atlantic Garbage Patch are two spaces where considerable amount of debris has been accumulated for years.

Marine life and its diversity are greatly dependent of various ocean currents. Many types of fishes, turtles and jellyfishes follow the currents to change places. Some species use these currents to breed.

Study of Ocean currents are an important part of meteorology. By checking these streams weather can be forecasted in some areas. It is also important to know the health of our oceans.

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