Ocean currents

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Ocean currents

• Moving seawater
• Surface ocean currents
• Transfer heat from warmer to cooler areas
• Similar to pattern of major wind belts
• Affect coastal climates
• Deep ocean currents
• Provide oxygen to deep sea
• Affect marine life

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Ocean currents

• Surface currents
• Affect surface water within and above the
  pycnocline (10 of ocean water)
• Driven by major wind belts of the world
• Primarily horizontal motion
• Deep currents
• Affect deep water below pycnocline (90 of ocean
  water)
• Driven by density differences caused by
  differences in temperature and salinity
• Larger and slower than surface currents
• Vertical and horizontal motions

3
Surface currents

• Frictional drag between wind and ocean
• Wind plus other factors such as
• Distribution of continents
• Gravity
• Friction
• Coriolis effect cause
• Gyres or large circular loops of moving water

4
Measuring surface currents

• Direct methods
• Floating device tracked through time
• Fixed current meter
• Indirect methods
• Pressure gradients
• Radar altimeters
• Doppler flow meter

Fig. 7.1a
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Measuring surface currents

• Direct methods
• Float meters
• Intentional
• Inadvertent
• Propeller meters
• Indirect methods
• Pressure gradients
• Satellites
• Doppler flow meters

Figure 7B
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Surface currents closely follow global wind belt
pattern

• Trade winds at 0-30º blow surface currents to the
  west
• Prevailing westerlies at 30-60º blow currents to
  the east

Figure 7-3
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Wind-driven surface currents
Figure 7-4
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Current gyres

• Gyres are large circular-moving loops of water
• Subtropical gyres
• Five main gyres (one in each ocean basin)
• North Pacific
• South Pacific
• North Atlantic
• South Atlantic
• Indian
• Generally 4 currents in each gyre
• Centered at about 30º north or south latitude

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Current gyres

• Gyres (continued)
• Subpolar gyres
• Smaller and fewer than subtropical gyres
• Generally 2 currents in each gyre
• Centered at about 60º north or south latitude
• Rotate in the opposite direction of adjoining
  subtropical gyres

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Ekman spiral

• Ekman spiral describes the speed and direction of
  flow of surface waters at various depths
• Factors
• Wind
• Coriolis effect

Figure 7-6
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Ekman transport

• Ekman transport is the overall water movement due
  to Ekman spiral
• Ideal transport is 90º from the wind
• Transport direction depends on the hemisphere
• Internet visualization

Figure 7-6
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