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Chapter 7 Ocean Circulation. Essentials of Oceanography 7 th Edition. Ocean currents. Surface currents Affect surface water within and above the pycnocline (10% of ocean water) Driven by major wind belts of the world Deep currents Affect deep water below pycnocline (90% of ocean water)

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Chapter 7 Ocean Circulation


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chapter 7 ocean circulation

Chapter 7 Ocean Circulation

Essentials of Oceanography

7th Edition

ocean currents
Ocean currents
  • Surface currents
    • Affect surface water within and above the pycnocline (10% of ocean water)
    • Driven by major wind belts of the world
  • Deep currents
    • Affect deep water below pycnocline (90% of ocean water)
    • Driven by density differences
    • Larger and slower than surface currents
measuring surface currents
Measuring surface currents
  • Direct methods
    • Float meters
      • Intentional
      • Inadvertent
    • Propeller meters
  • Indirect methods
    • Pressure gradients
    • Satellites
    • Doppler flow meters

Figure 7B

surface currents closely follow global wind belt pattern
Surface currents closely follow global wind belt pattern
  • Trade winds at 0-30º blow surface currents to the east
  • Prevailing westerlies at 30-60º blow currents to the west

Figure 7-3

current gyres
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
current gyres1
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
ekman spiral
Ekman spiral
  • Ekman spiral describes the speed and direction of flow of surface waters at various depths
  • Factors:
    • Wind
    • Coriolis effect

Figure 7-6

ekman transport
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

geostrophic flow and western intensification
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 Earth’s rotation
  • Western boundary currents are intensified

Figure 7-7

western intensification of subtropical gyres
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
currents and climate
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

upwelling and downwelling
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
coastal upwelling and downwelling
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

other types of upwelling
Other types of upwelling
  • Equatorial upwelling
  • Offshore wind
  • Sea floor obstruction
  • Sharp bend in coastal geometry

Equatorial upwelling

Figure 7-9

the gulf stream and sea surface temperatures
The Gulf Stream and sea surface temperatures
  • The Gulf Stream is a warm, western intensified current
  • Meanders as it moves into the North Atlantic
  • Creates warm and cold core rings

Figure 7-16

el ni o southern oscillation enso
El Niño-Southern Oscillation (ENSO)
  • El Niño = warm surface current in equatorial eastern Pacific that occurs periodically around Christmastime
  • Southern Oscillation = change in atmospheric pressure over Pacific Ocean accompanying El Niño
  • ENSO describes a combined oceanic-atmospheric disturbance
the 1997 98 el ni o
The 1997-98 El Niño
  • Sea surface temperature anomaly map shows warming during severe 1997-98 El Niño
  • Internet site for El Niño visualizations
  • Current state of the tropical Pacific

Figure 7-19a

el ni o r ecurrence interval
El Niño recurrence interval
  • Typical recurrence interval for El Niños = 2-12 years
  • Pacific has alternated between El Niño and La Niña events since 1950

Figure 7-20

indian ocean surface currents
Indian Ocean surface currents

Northeast monsoon

Southwest monsoon

Figure 7-23

deep currents
Deep currents
  • Deep currents:
    • Form in subpolar regions at the surface
    • Are created when high density surface water sinks
    • Factors affecting density of surface water:
      • Temperature (most important factor)
      • Salinity
    • Deep currents are also known as thermohaline circulation
deep ocean characteristics
Deep ocean characteristics
  • Conditions of the deep ocean:
    • Cold
    • Still
    • Dark
    • Essentially no productivity
    • Sparse life
    • Extremely high pressure
identification of deep currents
Identification of deep currents
  • Deep currents are identified by measuring temperature (T) and salinity (S), from which density can be determined

Figure 7-24

end of chapter 7

End of Chapter 7

Essentials of Oceanography

7th Edition