Ocean Circulation
Currents
Currents
• Horizontally
• Vertically
The Forces That Drive Currents
• Primary forces
– Starts water movement and determine its velocity
• Stress of wind
• Secondary forces
– Influence the direction and nature of flow
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Coriolis effect
gravity
friction
shape of ocean basins
Surface currents
• Wind
• Surface currents
– rapid with well defined boundaries
– slow and diffuse
– horizontal or vertical
• Gyre
Bottom Currents
• Driven by the force of gravity - dense water
sinks and less dense water rises
Flow within a Gyre
• North Atlantic gyre
– Four inter connected currents
• Eckman spiral
• Eckman transport
Geostrophic Gyres
• Geostrophic Gyre
– 5 Geostrophic gyre
• North Atlantic gyre
• South Atlantic gyre
• North Pacific gyre
• South Pacific gyre
• Indian Ocean gyre
– Geostrophic gyres independent of each other in each hemisphere
• Geostrophic currents
• 6 current circuits in the world ocean
– 2 in Northern hemisphere 4 in southern hemisphere
Currents within Gyres
• Western boundary Currents
• Eastern Boundary Currents
• Transverse currents
Western Boundary Currents
• Fastest and deepest
• Found at the western boundaries of the Ocean
basins
• Narrow
• Move warm water poleward in each gyre
Western boundary currents
• Five western boundary currents
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Gulf stream
Japan or Kuroshio current
Brazil current
Agulhas current
East Australian current
• Sverdrup
• Eddies
– Cold core eddies
– Warm core eddies
Eastern Boundary Currents
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The Canary Current
The Benguela Current
California Current
West Australian Current
The Peru or Humboldt Current
Eastern Boundary Currents
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Carry cold water equatorward
Shallow and broad
Boundaries not well defined
Eddies tend not to form
Westward Intensification
• The converging flow of the trade winds on
either side of equator
• The rotation of the earth
Transverse Currents
• Currents that flow from east to west
– Linking the eastern and western boundary
currents
• Counter Currents
• Under Currents
Exceptional Surface Currents
• Monsoon Currents
• High Latitude Currents
Effects of Surface Currents on
Climate
• Distribute tropical heat
• Influences climate and weather
Wind-Induced Vertical
Circulation
• Upwelling
– Equatorial upwelling
– Coastal upwelling
• Downwelling
Langmuir Circulation (page 222 fig 9.16)
• Langmuir Circulation
El Nino
Thermohaline Circulation
• Density driven
Water Masses
• Five common water masses
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Surface water
Central water
Intermediate water
Deep water
Bottom water
Formation and downwelling of
Deep water
• Antarctic bottom water
• North Atlantic deep water
Thermohaline Circulation Patterns
• Low and mid latitudes
• Caballing
• Contour currents
Studying Currents
• Float method
• Flow method
• Acoustical Tomography