UPSC Prelims 2012 Q45: Geography – Oceanography
Consider the following factors :
1. Rotation of the Earth
2. Air pressure and wind
3. Density of ocean water
4. Revolution of the Earth
Which of the above factors influence the ocean currents?
- (a) 1 and 2 only
- (b) 1, 2 and 3
- (c) 1 and 4
- (d) 2, 3 and 4
Answer: (b) 1, 2 and 3
Explanation
Factors that influence ocean currents
| Factor | Influences currents? | How |
|---|---|---|
| 1. Rotation of the Earth | Yes | The Coriolis force turns currents right in the north and left in the south |
| 2. Air pressure and wind | Yes | Planetary winds push the surface water |
| 3. Density of ocean water | Yes | Differences in temperature and salinity make water sink or rise |
| 4. Revolution of the Earth | No | Revolution causes seasons, not currents |
Two groups of forces:
| Group | Forces |
|---|---|
| Primary (start the movement) | Heating by the Sun, wind, gravity, Coriolis force |
| Secondary (shape the flow) | Density differences, shape of coasts |
Answer: (b) 1, 2 and 3.
Why each option is right or wrong
- (a) Incorrect. Density of ocean water also influences currents.
- (b) CORRECT. Rotation, air pressure and wind, and density all influence ocean currents.
- (c) Incorrect. Revolution of the Earth does not drive ocean currents.
- (d) Incorrect. Revolution is not a factor, and rotation is left out.
Key point
Ocean currents: wind, Coriolis force (rotation), density (temperature and salinity), gravity, coastline. Revolution of the Earth plays no part.
Remember
Currents: wind, rotation, density. Not revolution.
Common mistakes
- Mixing up rotation (daily spin) with revolution (yearly orbit).
- Forgetting density, which drives the deep currents.
- Thinking wind alone moves the oceans.
Exam tip
Rotation gives the Coriolis force; revolution gives the seasons. Only the first moves currents.
Sources
- NCERT Class XI — Fundamentals of Physical Geography, Ch 14 (Movements of Ocean Water)
- G.C. Leong — Certificate Physical and Human Geography, Ch on The Oceans