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Ocean Circulation


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Ocean Circulation

  1. 1. Chapter 8: Ocean CirculationFig. 8-26
  2. 2. Ocean currents move largeamounts of water and heat Wind-drivensurface oceancirculation Density-drivendeep-oceancirculation Both redistributeheat from warmerregions to coolerFig. 8-16
  3. 3. Measuring ocean currents Direct measurement Floating objects/instruments Fixed instruments Indirect measurement Distribution of density Satellite data Doppler flow meter Chemical tracers Distinctive water masses
  4. 4. Surface currents Frictional drag due to winds Surface currents similar to global winds Continents affect surface currentpatterns Other factors:GravityFrictionCoriolis Effect
  5. 5. Subtropical gyres Large circular flow Clockwise in northern oceans,e.g., North Atlantic Counterclockwise in southernoceans, e.g., South Atlantic 4 main currents in each gyre
  6. 6. Ekman spiral and Ekmantransport  Ekman transportmoves surfaceseawater about90oto the right ofthe wind in theNorthernHemisphere 90oleft inSouthernHemisphereFig. 8-6a
  7. 7. Western intensification “Hill” of seawater is steeper on western side Western currents are fast, narrow, deep
  8. 8. Subtropical gyres Ekman transportpiles up “hill” ofseawater at about30oN and S Water flows downhillunder gravity andveers right (Northernhemisphere) due toCoriolis Effect Circular flow Fig. 8-7
  9. 9. Upwelling Ekman transportmoves seawateroffshore Ekman transportmoves seawateraway fromanother watermassFig. 8-11a
  10. 10.  Cooler, nutrient-rich water risesvertically towardsea surface High biologicproductivity DownwellingoppositeFig. 8-11b
  11. 11. Surface currents Pattern similar in major oceanbasins Northern ocean gyre movesclockwise Southern ocean gyre movescounter-clockwise
  12. 12. Antarctic circulation Antarctic Circumpolar Current (orWest Wind Drift) Greatest volume Connects main oceans East Wind Drift Antarctic Divergence (upwelling)
  13. 13. North Atlantic Circulation North Equatorial Current Gulf Stream North Atlantic Current Gulf Stream and North AtlanticCurrents warm Europe Canary Current
  14. 14. North Equatorial Current
  15. 15. Gulf Stream
  16. 16. North Atlantic Current
  17. 17. Canary Current
  18. 18. South Atlantic Ocean South Equatorial Current Brazil Current Antarctic Circumpolar Current Greatest volume Connects three main oceans Benguela Current
  19. 19. South Equatorial current
  20. 20. Brazil Current
  21. 21. Benguela Current
  22. 22. North Pacific Ocean North Equatorial Current Kuroshio Current North Pacific Current California Current Strong Equatorial Counter Current
  23. 23. South Pacific Ocean South Equatorial Current East Australian Current Antarctic Circumpolar Current Peru Current Strong Equatorial Counter Current
  24. 24. ENSO El Niño-SouthernOscillation Irregular shift in ocean andatmosphere characteristics every 2-10 years Affects global climate Harmful and beneficialconsequences
  25. 25. El Niño ENSO Warm Phase Most obvious in Equatorial Pacific Pacific Warm Pool moves eastward acrossEquatorial Pacific Changes in pattern of upwelling/downwellingin eastern Pacific OceanFig. 8-2
  26. 26. ENSO warm phase effects Warmer seawater higher sea level Warmer seawater less upwelling ineastern Pacific Lower biologic productivity Warmer seawater kills some marine life Shift in atmosphere pressure Shift in areas of precipitation
  27. 27. La Niña ENSO Cool Phase Stronger tradewinds Warm pool stays in western Pacific Increased upwelling in eastern Pacific Shift in precipitation patterns Shift in atmospheric pressure
  28. 28. ENSO data collection TOGA Tropical Ocean GlobalAtmosphere TAO Tropical Atmosphere Ocean Monitor ocean and atmosphere Data indicate what phase ENSO Pacific Decadal Oscillation Decades-long cycles of warmingand cooling in Pacific Ocean
  29. 29. Indian Ocean Circulation North and South Equatorial Currents Equatorial Counter Current Agulhas Current Antarctic Circumpolar Current West Australian Seasonal shifts (monsoons) of windsand currents
  30. 30. Thermohaline circulation 90% of world ocean Below pycnocline Large volumes ofseawater Extremely slowspeed Each ocean basin issimilar in deep-ocean circulation
  31. 31. Sources of deep water Densest seawater is cold Most deep water masses frompolar oceans Sink to density level and movehorizontally
  32. 32. Antarctic Bottom Water Densest deep water(coldest) Sinks aroundAntarctica Most widespreaddeep-water mass Found as far as40oN Carries O2 into deepocean Fig. 8-25
  33. 33. North Atlantic Deep Water Complex mixtureof cold seawaterfrom Norwegiansea mixing with Gulf Stream MediterraneanIntermediateWater Other NA watermasses Extends fromNorth Atlantic toabout 40osouth
  34. 34. Intermediate Water Masses Antarctic Intermediate Water Sinks at Antarctic Convergence Cold Salinity less than average Mediterranean Intermediate Water Warm Very salty
  35. 35. Conveyor Belt Circulation Mixture of surfaceocean circulationand deep-oceancirculation Mixes surfaceand deep Mixes waters indifferent oceans Fig. 8-26
  36. 36. Langmuir Circulation Alternately converging and divergingconvection cells Wind blowing over calm ocean Alternate rows of upwelling and downwelling
  37. 37. End of Chapter 8: OceanCirculation