https://www.insightsonindia.com/2020/03/29/secure-synopsis-24-march-2020/
- There are a variety of factors that affect how ocean currents (water in motion) are created, including a combination of two or more factors.
- The different types of currents (referred to as surface or thermohaline, depending on their depth) are created by, among other things, wind, water density, the topography of the ocean floor and the coriolis effect.
Primary Forces Responsible for Ocean Currents:
Insolation
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- Heating by solar energy causes the water to expand. That is why, near the equator the ocean water is about 8 cm higher in level than in the middle latitudes.
- This causes a very slight gradient and water tends to flow down the slope. The flow is normally from east to west.
Wind (atmospheric circulation)
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- Wind blowing on the surface of the ocean pushes the water to move. Friction between the wind and the water surface affects the movement of the water body in its course.
- Winds are responsible for both magnitude and direction [Coriolis force also affects direction] of the ocean currents. Example: Monsoon winds are responsible for the seasonal reversal of ocean currents in the Indian ocean.
- The oceanic circulation pattern roughly corresponds to the earth’s atmospheric circulation pattern.
- The air circulation over the oceans in the middle latitudes is mainly anticyclonic [Sub-tropical High Pressure Belt] (more pronounced in the southern hemisphere than in the northern hemisphere due to differences in the extent of landmass). The oceanic circulation pattern also corresponds with the same.
- At higher latitudes, where the wind flow is mostly cyclonic [Sub-polar Low Pressure Belt], the oceanic circulation follows this pattern.
- In regions of pronounced monsoonal flow [Northern Indian Ocean], the monsoon winds influence the current movements which change directions according to seasons.
Gravity:
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- Gravity tends to pull the water down to pile and create gradient variation.
Coriolis force:
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- The Coriolis force intervenes and causes the water to move to the right in the northern hemisphere and to the left in the southern hemisphere.
- These large accumulations of water and the flow around them are called Gyres. These produce large circular currents in all the ocean basins. One such circular current is the Sargasso Sea.
Shape of the Ocean basins:
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- Another major factor that determines the direction of surface currents is the shape of ocean basins.
- When a surface current collides with land, it changes the direction of the currents. Imagine pushing the water in a bathtub towards the end of the tub.
- When the water reaches the edge, it has to change direction.
Secondary Forces Responsible for Ocean Currents:
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- Temperature difference and salinity difference are the secondary forces.
- Differences in water density affect vertical mobility of ocean currents (vertical currents).
- Water with high salinity is denser than water with low salinity and in the same way cold water is denser than warm water.
- Denser water tends to sink, while relatively lighter water tends to rise.
- Cold-water ocean currents occur when the cold water at the poles sinks and slowly moves towards the equator.
- Warm-water currents travel out from the equator along the surface, flowing towards the poles to replace the sinking cold water.
