OCEAN CURRENTS
Geography
Ocean currents are the continuous, predictable and directional movement of seawater.
They are like rivers flowing inside oceans.
They involve massive movement of ocean water driven by various forces.
Ocean water moves in two directions:
- Horizontal movements are called ocean currents.
- Vertical movements are called upwelling and downwelling.
Ocean currents influence:
- Global climate
- Rainfall patterns
- Marine life distribution
- Human activities like fishing and navigation
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TYPES OF OCEAN CURRENTS
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1. Based on Depth
A. Surface Currents
- Form about 10% of total ocean water
- Occupy upper 400 meters of ocean
- Mainly driven by winds
- Affect climate directly
B. Deep Water Currents
- Form about 90% of ocean water
- Move due to differences in density and gravity
- Density difference depends on temperature and salinity
- Cold, dense water sinks at high latitudes and moves toward equator
2. Based on Temperature
A. Cold Currents
- Flow from high latitudes to low latitudes
- Bring cold water into warm regions
- Usually found on west coasts of continents in low and middle latitudes
- Also found on east coasts in high latitudes (Northern Hemisphere)
- Examples: Peruvian Current, Canary Current, Benguela Current
B. Warm Currents
- Flow from low latitudes to high latitudes
- Bring warm water into cold regions
- Usually found on east coasts of continents in low and middle latitudes
- In Northern Hemisphere, found on west coasts in high latitudes
- Examples: Gulf Stream, Kuroshio Current
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FORCES RESPONSIBLE FOR OCEAN CURRENTS (PRIMARY FORCES)
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1. Influence of Insolation
- Solar heating causes water to expand
- Sea level near equator is about 8 cm higher than mid-latitudes
- Creates slight slope and water flows downslope
- Flow is generally east to west
2. Influence of Wind (Atmospheric Circulation)
- Wind pushes surface water due to friction
- Winds control both magnitude and direction of currents
- Coriolis force also affects direction
- Example: Monsoon winds cause seasonal reversal of currents in Indian Ocean
- Ocean circulation roughly matches atmospheric circulation pattern
- Subtropical high pressure belts produce anticyclonic circulation
- Subpolar low pressure belts produce cyclonic circulation
3. Influence of Gravity
- Gravity pulls water from higher level to lower level
- Creates slope and gradient difference
4. Influence of Coriolis Force
- Deflects currents to the right in Northern Hemisphere
- Deflects currents to the left in Southern Hemisphere
- Produces large circular systems called Gyres
- Example: Sargasso Sea
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SECONDARY FORCES
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- Temperature difference
- Salinity difference
- Density difference
- Cold water is denser than warm water
- Salty water is denser than less salty water
- Dense water sinks, light water rises
- Cold water from poles sinks and moves toward equator
- Warm surface water from equator moves toward poles
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CAUSES OF OCEAN CURRENTS
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1. Planetary Winds
- Constant winds drag surface water
- Most currents follow direction of prevailing winds
- Trade winds create equatorial currents
- Westerlies create North Atlantic Drift and North Pacific Current
2. Variation in Temperature
- Equatorial water is warm and light
- Polar water is cold and dense
- Light water moves poleward, dense water moves equatorward
3. Variation in Salinity
- High salinity water sinks
- Low salinity water rises
- Surface currents move from low salinity to high salinity
- Example: Atlantic water flows into Mediterranean Sea
4. Rotation of Earth
- Produces Coriolis force
- Deflects currents right in north, left in south
- Creates counter-equatorial currents
5. Configuration of Coastline
- Shape of coast changes direction of currents
- Example: Brazilian coast splits equatorial current into Caribbean and Brazilian currents
- Monsoon currents follow Indian coastline
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DESERT FORMATION AND OCEAN CURRENTS
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- Hot deserts lie between 15° and 30° latitudes
- Found on western margins of continents
- Examples:
Sahara, Arabian, Thar, Kalahari, Namib, Atacama, Australian Desert
Reasons:
- Presence of subtropical high pressure belts (descending air)
- Offshore trade winds
- Cold currents reduce rainfall and create fog instead of rain
- Relative humidity becomes very low
- Example:
Peruvian Current causes extreme dryness in Atacama Desert (rainfall only 1.3 cm)
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ATLANTIFICATION
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- Warm Atlantic water flows into Arctic through Barents Sea
- Earlier it stayed below cold Arctic water
- Now it is rising upward
- Heat melts sea ice from below and prevents new ice formation
- This process is called Atlantification
- Arctic ice is now attacked from:
- Top by warm atmosphere
- Bottom by warm ocean
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Subject: Geography
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