Prelims 2012 · archive
EasyConsider 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?
Answer & explanation
Answer: (b) 1, 2 and 3
Ocean currents are driven by winds, which come from air-pressure differences. The Earth's rotation (the Coriolis force) deflects them, and density differences in sea water (temperature and salinity) move water vertically and horizontally. The Earth's revolution round the Sun is not a driver of currents.
- ✓ 1. The Earth's rotation produces the Coriolis force. This deflects moving water and, together with the winds, helps shape the large circular gyres of the ocean basins.
- ✓ 2. Winds, which arise from air-pressure differences, are the main driver of surface currents. Their frictional drag pulls the surface water along.
- ✓ 3. Differences in temperature and salinity change the density of sea water. Dense water sinks and spreads, which drives deep (thermohaline) circulation.
- ✗ 4. The Earth's revolution round the Sun is linked to the seasons. It is not a force that moves ocean water.
- ✗ (d) This option drops rotation (factor 1) and wrongly includes revolution (factor 4).
Remember · Ocean currents come from wind, Earth's rotation (Coriolis force) and density differences from temperature and salinity. Revolution of the Earth is not a cause.
Sources
- NASA GISS – ICP: General Characteristics of the World's Oceans – Ocean Currents ↗ “The driving force of currents is the frictional drag of winds, along with the interplay of the Coriolis force, density differences caused by temperature and salinity”
- NASA (mynasadata) – Ocean Circulation Patterns ↗ “Instead, they currents are deflected because of the Coriolis force, which is due to the Earth's rotation.”
Question: UPSC Civil Services (Preliminary) 2012, General Studies paper. Explanation: Minimalist IAS, checked 25 Oct 2026 (how we verify). ·