What are Ocean Currents?
Ocean currents can be defined as streams comprising vertical as well as horizontal components that make up the ocean water’s circulation system. The circulation of ocean waters can be due to a wide variety of factors such as variations in the water density in the ocean’s different parts, wind friction, gravity, etc.
Ocean currents play a major role in transferring a significant amount of heat from the equatorial areas of the Earth to the poles, much akin to atmospheric winds. The climates of the coastal areas are thus, majorly determined by the ocean currents.
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Information About Ocean Currents
The average seawater movement is determined by the ocean’s general circulation. The horizontal movements in circulation are termed currents whereas the vertical movements are called downwelling or upwelling. The range of horizontal movements varies from a few centimetres to about 4 metres per second. Vertical movements, on the other hand, run at very low speeds varying only up to a few metres a month. The vertical movements are also associated with the regions where the horizontal flow patterns converge and diverge given that seawater is almost incompressible.
Causes of Ocean Currents
Ocean currents are caused primarily due to the following factors
Gravity
Horizontal Pressure Gradient
Coriolis Forces
Frictional Forces
Gravity: This is the major factor behind density-driven ocean currents. The denser water falls while the less dense water is pushed away by gravity. This causes the less dense water to shoot and rise sideways. As the lighter and hotter water of less salty regions rise and flow in order to replace the heavier and colder or more salty regions of water, huge convection loops ocean currents are formed. Sun’s heat, differences in salinity and Earth’s gravity, thus interact, leading to the formation of ocean currents.
Horizontal Pressure Gradient: Variations in salinity and temperature of ocean water give rise to differences in density horizontally. When this difference in density is measured along a specific depth, it causes the hydrostatic pressure to vary horizontally giving rise to horizontal pressure gradients and ultimately ocean currents. These horizontal pressure gradients when compared to the vertical changes in pressure are, however, much smaller.
Coriolis Force: Named after a French Mathematician and engineer of the 19th century, Gustave-Gaspard Coriolis, the Coriolis forces are an important factor causing ocean currents. Earth’s rotation generates Coriolis force that acts on particles depicting movement in any horizontal direction. The nature of this force is perpendicular thus causing objects to move in great circles on the earth’s surface. Owing to the Coriolis forces, the major ocean currents in the northern part of the earth’s hemisphere rotate in a clockwise direction while in the southern hemisphere, they rotate in an anti-clockwise direction. The Coriolis forces are inertial forces that are generated from the earth being in a rotating frame of reference. The Coriolis force also deflects the ocean currents by about 45o from the direction of the wind in the northern and the southern hemispheres while at the equator the apparent horizontal reflection would be zero. span>
Frictional Forces: Friction acts to slow down water movement through the oceans if the velocity of the surrounding fluid is different. While a layer of fluid that is moving fast tends to drag a layer moving slowly, the layer that is moving slowly will tend to reduce the speed of the faster-moving layer. This transfer of momentum between the different layers is called frictional force. The wind that blows over the surface of the seawater is responsible for the transferring of momentum to the water. The wind stress or the frictional force present at the surface of the sea, on the other hand, generated the wind-driven circulation. Boundary layer frictional forces also influence the currents that move along the ocean floor and its sides. The momentum from the ocean waters’ circulation is removed by the stationary ocean floor.
Effects of Ocean Currents
The effects of ocean currents are profound and varied. Ocean currents are the major driving forces of the weather patterns on earth except for the equatorial areas. They act akin to a conveyor belt as ocean currents transport precipitation and warm water from the equator towards the poles bringing the cold water from the poles to the tropics.
Ocean currents are thus responsible for regulating the global climate as they help counteract the solar radiation that is unevenly distributed across the surface of the earth. The effect of ocean currents is so huge that without them we would experience extreme regional temperatures, making the Earth a much less inhabitable place.
Ocean currents are also responsible for rainfall in the coastal regions as the winds that blow over the warm currents become laden with moisture. Similarly, the cold currents are responsible for the drier arid climate of the deserts. Another important effect of ocean currents is the formation of fog as a result of the meeting of the cold and the warm currents, planktons are also formed as a result of this meeting leading to an abundance of fish in such areas.
FAQs on Causes of Ocean Currents
1. What are the main causes of ocean currents as per the Geography syllabus?
The causes of ocean currents are broadly classified into two categories: primary forces that initiate water movement and secondary forces that modify the flow. The main causes include:
- Solar Heating: The sun heats equatorial water, causing it to expand and create a slight gradient, initiating movement towards the poles.
- Wind: The friction between wind and the ocean surface pushes the water, creating surface currents.
- Gravity: Gravity pulls water down from elevated areas, influencing the direction of flow.
- Coriolis Force: Due to the Earth's rotation, this force deflects currents, shaping their path.
- Differences in Density: Variations in water temperature and salinity create density differences, causing vertical currents as denser water sinks.
2. What is the difference between the primary and secondary forces that cause ocean currents?
The main difference lies in their function. Primary forces are responsible for initiating the movement of ocean water. These include solar energy, wind, and gravity. In contrast, secondary forces do not start the movement but influence or modify the direction and speed of the currents once they are in motion. The most significant secondary force is the Coriolis force, which alters the path of the currents.
3. How does wind specifically contribute to the formation and direction of ocean currents?
Wind causes ocean currents by exerting stress on the ocean's surface through friction. As the wind blows, it drags the surface water along with it, creating large-scale surface currents. The energy transferred from the wind to the water is the primary driver for major surface circulation patterns, such as the large circular currents known as gyres. The prevailing wind patterns, like the trade winds, are directly responsible for the general direction of these surface currents.
4. Why is the Coriolis force a crucial factor in determining the path of ocean currents?
The Coriolis force is crucial because it prevents ocean currents from moving in straight lines. Caused by the Earth's rotation, this force deflects moving objects, including water, to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This deflection is responsible for the large, circular flow of currents within ocean basins, forming gyres and dictating the overall global circulation pattern rather than a simple north-south movement.
5. How do differences in water temperature and salinity create deep ocean currents?
Differences in temperature and salinity (salt content) drive deep ocean currents through a process called thermohaline circulation. Water that is cold and has high salinity is denser than warm, less salty water. In polar regions, this cold, dense water sinks towards the ocean floor. This sinking action displaces water below, initiating a slow-moving, deep-water current that circulates around the globe, acting like a global conveyor belt that transfers heat and nutrients.
