Surface currents closely follow global wind belt pattern

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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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Geostrophic flow and western intensification

• Geostrophic flow causes a hill to form in
  subtropical gyres
• The center of the gyre is shifted to the west
  because of Earths rotation
• Western boundary currents are intensified

Figure 7-7
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Western intensification of subtropical gyres

• The western boundary currents of all subtropical
  gyres are
• Fast
• Narrow
• Deep
• Western boundary currents are also warm
• Eastern boundary currents of subtropical gyres
  have opposite characteristics

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Currents and climate

• Warm current ? warms air ? high water vapor ?
  humid coastal climate
• Cool current ? cools air ? low water vapor ? dry
  coastal climate

Figure 7-8a
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Upwelling and downwelling

• Vertical movement of water (?)
• Upwelling movement of deep water to surface
• Hoists cold, nutrient-rich water to surface
• Produces high productivities and abundant marine
  life
• Downwelling movement of surface water down
• Moves warm, nutrient-depleted surface water down
• Not associated with high productivities or
  abundant marine life

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Coastal upwelling and downwelling

• Ekman transport moves surface water away from
  shore, producing upwelling
• Ekman transport moves surface water towards
  shore, producing downwelling

Figure 7-11
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Other types of upwelling

• Equatorial upwelling
• Offshore wind
• Sea floor obstruction
• Sharp bend in coastal geometry

Equatorial upwelling
Figure 7-9
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