Ocean Currents
Category: GS-1 (Geography), GS-3 (Environment)
1. What are Ocean Currents?
Ocean currents are continuous, large-scale, directional movements of seawater, comparable to river flows in oceans. These movements can be horizontal (currents) or vertical (upwelling/downwelling), driven by several environmental forces.
2. Factors Influencing Ocean Currents
Primary Forces
- Solar Heating: Causes water expansion near the equator, creating slopes in sea level.
- Wind: Surface winds exert friction and push surface waters.
- Gravity: Pulls water down the gradient created by heating.
- Coriolis Effect: Deflects currents rightward in the Northern Hemisphere and leftward in the Southern Hemisphere.
Secondary Forces
- Water Density: Controlled by temperature and salinity.
- Thermohaline Circulation: Movement caused by temperature (thermo) and salinity (haline) differences.
3. Types of Ocean Currents
By Depth
- Surface Currents: Top 400m of ocean water; influenced by global wind belts.
- Deep Water Currents: Driven by thermohaline forces; forms the Global Conveyor Belt.
By Temperature
- Warm Currents: Move from equator towards poles.
- Cold Currents: Move from poles toward the equator.
4. Major Ocean Currents
| Current | Type | Region | Remarks |
|---|---|---|---|
| Gulf Stream | Warm | North Atlantic | Western intensified, keeps Europe warm |
| Labrador Current | Cold | North Atlantic | Meets Gulf Stream; rich fishing zones |
| Canary Current | Cold | North Africa | Promotes desertification (Sahara) |
| North Atlantic Drift | Warm | Europe | Extension of Gulf Stream |
| Peru (Humboldt) Current | Cold | West South America | Major upwelling; El Niño impact zone |
| Brazil Current | Warm | East South America | Meets Falkland Current, temperate sea |
| Falkland (Malvinas) Current | Cold | South Atlantic | Part of ACC; affects Argentina's climate |
| California Current | Cold | West North America | Upwelling; fishing zones |
| Kuroshio (Japan) Current | Warm | West Pacific | Gulf Stream of Pacific |
| Oyashio Current | Cold | East Asia | Rich in nutrients, collides with Kuroshio |
| Agulhas Current | Warm | East Africa | Fastest western boundary current |
| Benguela Current | Cold | Southwest Africa | Famous upwelling zone |
| Somali Current | Warm | Indian Ocean | Monsoon-driven seasonal current |
| East Australian Current | Warm | East Australia | Sub-tropical marine fauna transport |
| West Australian Current | Cold | Western Australia | Part of West Wind Drift |
| Equatorial Currents | Warm | Global Equator | Includes North, South Equatorial and Counter Currents |
| Antarctic Circumpolar Current (ACC) | Cold | Southern Ocean | Only unbroken current around globe |
5. Effects of Ocean Currents
- Climate Regulation: Warm currents warm coastal areas; cold currents cool them.
- Rainfall: Warm currents enhance rainfall; cold currents suppress it (e.g., Kalahari Desert).
- Fishing: Mixing zones create rich plankton zones (e.g., Grand Banks, Japan coast).
- Fog & Storms: Collision of warm and cold currents cause fog and violent storms.
- Trade Routes: Navigation is easier with favorable current flow.
- Desert Formation: Cold currents on west coasts contribute to aridity (e.g., Atacama Desert).
UPSC Potential Questions
- Prelims: Match the following currents to warm/cold types.
- Mains (GS1): "Discuss the role of ocean currents in climate and biodiversity." (150 words)
MCQs for Quick Revision
Q1. Which one of the following ocean currents is a cold current?
- Kuroshio Current
- Gulf Stream
- Humboldt Current
- Brazilian Current
Q2. The meeting of which two currents causes dense fog near Newfoundland?
- Labrador Current and Gulf Stream
- Kuroshio and Oyashio
- Brazil and Falkland Currents
- Agulhas and Benguela
