Q. Consider the following factors: - Rotation of the Earth
- Air pressure and wind
- Density of ocean water
- Revolution of the Earth
Which of the above factors influence the ocean currents? (UPSC Prelims 2012)
Answer:
1, 2 and 3
Notes: The correct answer is
[B] 1, 2 and 3. Ocean currents are influenced by a combination of "primary forces" that initiate water movement and "secondary forces" that influence the direction and speed of the flow.
- Rotation of the Earth (Factor 1 is Correct): The Earth's rotation causes the Coriolis effect, which deflects moving water to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This is a fundamental driver of the large, circular patterns of currents known as gyres.
- Air pressure and wind (Factor 2 is Correct): Surface ocean currents are primarily driven by the friction of wind blowing across the water. Prevailing winds, such as the Trade Winds and Westerlies, push the surface water in specific directions. Differences in air pressure also affect wind patterns, which in turn dictate current movement.
- Density of ocean water (Factor 3 is Correct): This is the driver of deep-ocean currents (thermohaline circulation). Variations in temperature and salinity change the density of water. Denser (colder or saltier) water sinks, while less dense water rises, creating a vertical "conveyor belt" of movement.
- Revolution of the Earth (Factor 4 is Incorrect): The Earth's revolution refers to its annual orbit around the Sun. While this causes seasons and affects solar insulation (which indirectly influences temperatures), it does not directly "force" or "influence" the mechanics of ocean current movement in the way that rotation or wind does.