Ocean currents refer to the steady movement or flow of surface ocean water in a prevailing direction. Various forces act upon ocean water, causing it to move. They include the wind, temperature, breaking waves and tides, and sometimes underground forces like earthquakes.
Ocean currents are the movements of ocean water due to gravity, the rotating earth (Coriolis effect), water density, the sun, and wind. The various forces determine the size, speed, direction, and shape of ocean currents. The water can either move horizontally – known as currents, or vertically – known as downwellings or upwellings.
Ocean currents are responsible for heat transfer, biodiversity variations, and the planet’s climate.
In this article, we look at how ocean currents affect climate, the importance of ocean currents, and the types, causes, and effects of ocean currents.
According to Wikipedia,
“An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences. Depth contours, shoreline configurations, and interactions with other currents influence a current’s direction and strength. Ocean currents are primarily horizontal water movements.“
Types of Ocean Currents
Ocean currents can be classified as either horizontal or vertical. Let’s take a close look at each of them:
These include surface and deep-water currents.
1. Surface Currents
They are currents that occur on the top layer of the ocean and are primarily driven by wind. They affect the water in the upper 300m of the ocean. The currents mirror the large-scale circulation of air, mostly derived from unequal heating of the planet’s surface by the sun.
The currents, therefore, form rotating systems in the middle of the ocean systems, called gyres. Surface currents are responsible for redistributing heat at a planetary scale.
2. Deep-water Currents
As opposed to surface currents that occur on the upper surface of the ocean, deep-water currents occur deep inside the ocean, beyond 300 meters. As they occur far below the surface, they are not influenced by the wind.
However, they arise as a result of variation in the density of the ocean water and are controlled by the temperature and salt content of the water.
This category of currents can either be upwelling or downwelling. Let’s see how they differ.
3. Upwelling Currents
Upwelling currents are currents that move from deep in the ocean, heading towards the surface. They are the ones responsible for bringing organic matter from below the ocean towards its surface.
In Antarctica, upwelling currents pump nitrogen and phosphates up from the deep sea to blooms of algae and other plants.
The planktons can then be eaten by crustaceans called krill, which in turn are eaten by penguins, seabirds, seals, and the baleen whales, the largest animals on earth.
4. Downwelling Currents
These currents move material from the ocean’s surface towards its floor. Surface water can be forced downwards by the pressure of the water when currents converge, or wind drives the ocean against a coastline.
It is important as the dissolved oxygen in the sediments and water below would quickly be used up by the decay of organic matter.
Additionally, anaerobic bacteria would take control of decomposition, contributing to a build-up of hydrogen sulfide, and only a handful of benthic animals would survive such toxic conditions.
Causes of Ocean Currents
Some of the common causes include the following:
1. Solar Heating
Solar heating causes water to expand. The water around the equator is roughly 8cm higher than in middle latitudes. It causes a slight slope in the water and flows down the slopes. Warm water flows towards the cold Polar Regions, and cold water flows towards the warmer equatorial regions.
The wind is responsible for ocean currents as it blows the water on the surface, causing the currents. The wind is responsible for surface currents, where ocean water is redistributed based on its density and temperature.
Gravity tends to pull items towards the surface of the earth. When the wind blows ocean water, the water piles up in the direction of the wind. In this scenario, gravity acts against the pressure gradient, pulling the water down the ‘hill.’
4. The Salinity of The Water
When water moves towards the poles, it gets cold and freezes into ice, leaving a share of salt behind. This makes the underlying water saltier, making it denser. The cold, saltier and denser water sinks to the ocean floor and is replaced by surface water.
Warm water tends to stay on the surface of the ocean. When the denser, saltier, and colder water moves towards the warmer area of the equator, it warms up and becomes less dense, rising to the ocean’s surface, resulting in upwellings.
6. Coriolis effect
Coriolis effect refers to the rotation of the earth. It produces forces on all bodies moving relative to the earth. As the earth is spherical, the forces are greatly felt at the poles and least at the equator.
The Coriolis effect also results in the wind changing direction, with Northern Hemisphere winds and currents moving towards the right while Southern Hemisphere currents are deflected to the left.
7. Underwater Earthquakes
Underwater earthquakes can trigger ocean currents, moving masses of water inland. Earthquakes can also trigger downslope movements of water-saturated sediments, resulting in strong turbidity currents.
Effects of Ocean Currents
The occurrence of ocean currents doesn’t go without effects. Some of the effects include:
1. They Result in Rain
Warm currents lead to evaporation, which turns into rain for the coastal areas. For instance, the North Atlantic Drift brings rainfall to Western parts of Europe, resulting in rains throughout the year.
2. They Can Also Cause Deserts
Cold currents do not give rise to moisture-laden winds, so there is no rainfall in the coastal regions. The conditions cause desertification in the affected coastal regions, such as the Kalahari and Patagonia Deserts, because of the cold Benguela and Falkland currents, respectively.
3. Currents Can Destroy Marine Wildlife
Some currents might be too strong and end up destroying plankton and other see creatures. For instance, El Nino currently destroys plankton along the Peruvian coasts. It also brings with it several diseases that kill fish.
4. Currents Help with The Continuity of Life
In Antarctica, strong upwelling currents pump nitrogen and phosphates up from the deep sea to blooms of algae and other plants. The planktons are eaten by crustaceans called krill. The krill, in turn, feed penguins, seabirds, seals, and the baleen whales – the largest animals on earth.
5. Currents Save up On Time and Costs
It goes to the advanced knowledge of currents by sailors. When currents are in their favor, they can reach their destinations in time. They can also reduce shipping time and fuel costs.
However, if they are against the sailors, it will take more time battling them, and use more fuel to sail past those currents
6. Currents Can Result in Deaths
Ocean currents can also result in deaths and destruction of property if they are strong enough to overpower ships in the ocean. Of course, to do so, they have to be very strong and probably accompanied by tremors or lightning, but in the end, they can lead to disastrous results.
Importance of Ocean Currents
Some of the significance of ocean currents include the following:
1. Controlling the Climate
Ocean currents are responsible for moving the heat from the equator and towards the poles. As such, they maintain the natural order and balance of the climate.
2. Critical to Marine Life
Marine wildlife is heavily dependent on the balance created by the ocean and is maintained by ocean currents. The currents carry nutrients and food organisms, feeding the plants and animals that depend on them.
They also carry reproductive cells and ocean life to new places. The best example is sea turtles that lay eggs in the sand along the shores of the ocean. The ocean currents then carry the young hatchlings into the water.
3. Currents Are Vital for Ports in The Polar Regions
Warm ocean currents are responsible for keeping the ports in polar regions operational. It is because they keep the ports ice-free. The North Atlantic Drift, for instance, keeps most of the European ports ice-free and operational. Norway is a prime beneficiary of this drift.
4. Dispersal of Life Forms
Ocean currents are also important as they disperse many life forms. For instance, the lifecycle of the European eel is highly sustained and influenced by ocean currents.
5. Transportation By Humans
Humans rely on ocean currents to move some sea vessels, such as boats, on water. Currents are also important as they help when docking and undocking boats, speeding up shipping lanes, and keeping the ships safe, primarily in narrow waterways.
The direction of currents can also help in search and rescue missions and environmental disaster clean-ups.
6. Currents Are Responsible for Some Sports
Not all sports are played on dry land. Some currents create waves that can be used for competitive sports or recreational activities such as surfing. When surfing, a surfer rides with or against the wave, helping carry the surfer to shore.
How Do Ocean Currents Affect the Climate?
Despite all the effects and benefits of ocean currents, they affect the climate in several ways:
1. Maintaining the Climate Around the Poles
Warm currents move toward the poles, while cold currents move toward the equator. Such movement ensures the climate around the poles is maintained and life around the area is not disrupted.
2. Causing Rains
Currents are also responsible for rain. Warm currents migrate from around the equator towards the poles, and at the same time, the warmth causes the water to evaporate. The same will result in rains around the coastal regions or the ocean.
3. Ocean Water Directs Ocean Currents
Ocean currents are continuously directed by the movement of ocean water. Forces acting on the water, such as its density, temperature, and salinity, among others, control the currents in the ocean.
4. They Create Global Conveyor Belts
The global conveyor belt is a system of deep and surface currents, which move water all over the globe. The currents circulate the globe and can be instrumental in determining the climate of a region.
For instance, the North Atlantic Drift brings rainfall to Western parts of Europe, and Benguela and Falkland’s currents cause desert conditions in the Kalahari and Patagonia Deserts, respectively.
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