Currents 1


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Currents 1

  1. 1. Ocean CirculationThis image shows the abundance of life in the sea, measured by the SeaWiFS instrument aboard the Seastar satellite.Dark blue represents warmer areas where there is little life due to lack of nutrients, and greens and reds representcooler nutrient-rich areas.The nutrient-rich areas include coastal regions where cold water rises from the sea floor bringing nutrients along andareas at the mouths of rivers where the rivers have brought nutrients into the ocean from the land.
  2. 2. Chapter Overview Ocean currents are moving loops of water. Surface currents are influenced by major wind belts. Currents redistribute global heat. Thermohaline circulation affects deep currents. Currents affect marine life. © 2011 Pearson Education, Inc.
  3. 3. What creates ocean currents?
  4. 4. Types of Ocean Currents Surface currents  Wind-driven  Primarily horizontal motion Deep currents  Driven by differences in density caused by differences in temperature and salinity  Vertical and horizontal motions © 2011 Pearson Education, Inc.
  5. 5. Measuring Surface Currents Direct methods  Floating device tracked through time  Fixed current meter Indirect methods  Pressure gradients  Radar altimeters  Doppler flow meter © 2011 Pearson Education, Inc.
  6. 6. Global Surface Current Flow © 2011 Pearson Education, Inc.
  7. 7. Measuring Deep Currents Floating devices tracked through time Chemical tracers (inadvertently added)  Tritium (radioactive isotope of H produced by nuclear bomb tests in 1950’s and 1960’s ) © 2011 Pearson Education, Inc.
  8. 8. • Chlorofluorocarbons (freons)
  9. 9. • Characteristic temperature and salinity
  10. 10. Argo - free drifting device that move vertically and measuretemperature, salinity, and other water characteristics of the upper 2000meters (6600 ft) of the ocean. Once deployes, each float sinks to aparticular depth, drifts for up to 10 days collecting data, then resurfacesand transmits data on its location and ocean variables. © 2011 Pearson Education, Inc.
  11. 11. Surface Currents Occur above pycnocline Frictional drag between wind and ocean Generally follow wind belt pattern Other factors:  Distribution of continents  Gravity  Friction  Coriolis effect © 2011 Pearson Education, Inc.
  12. 12. Subtropical Gyres Large, circular loops of moving water Bounded by:  Equatorial current  Western Boundary currents  Northern or Southern Boundary currents  Eastern Boundary currents Centered around 30 degrees latitude © 2011 Pearson Education, Inc.
  13. 13. Five Subtropical Gyres1. North Atlantic – Columbus Gyre2. South Atlantic – Navigator Gyre 13. North Pacific – 3 Turtle Gyre 5 44. South Pacific – Heyerdahl Gyre 25. Indian Ocean – Majid Gyre © 2011 Pearson Education, Inc.
  14. 14. Subtropical Gyres and Currents © 2011 Pearson Education, Inc.
  15. 15. Subtropical Gyre CurrentsFour main currents flowing into one another: Equatorial Currents  North or south  Travel westward along equator © 2011 Pearson Education, Inc.
  16. 16. Subtropical Gyre Currents  Western Boundary Currents – warm waters © 2011 Pearson Education, Inc.
  17. 17. Subtropical Gyre Currents  Northern or Southern Boundary Currents – easterly water flow across ocean basin © 2011 Pearson Education, Inc.
  18. 18. Subtropical Gyre Currents  Eastern Boundary Currents – cool waters © 2011 Pearson Education, Inc.
  19. 19. Gyres and Boundary Currents © 2011 Pearson Education, Inc.
  20. 20. Other Surface Currents Equatorial Countercurrents – eastward flow between North and South Equatorial Currents Subpolar Gyres  Rotate opposite subtropical gyres  Smaller and fewer than subtropical gyres © 2011 Pearson Education, Inc.
  21. 21. Current Ocean Basin Location (N, S, E, W)General Temp Flow Direction Wind -Driven Ocean Surface Currents (Warm or Cool) of the World Map relative to Equator (Away or Towards?)Gulf Stream Alantic West Warm Away
  22. 22. Ekman Spiral Surface currents move at an angle to the wind. The Ekman spiral describes speed and direction of seawater flow at different depths. Each successive layer moves increasingly to the right in the Northern Hemisphere  Coriolis effect © 2011 Pearson Education, Inc.
  23. 23. Ekman Transport Average movement of seawater under influence of wind 90 degrees to right of wind in Northern hemisphere 90 degrees to left of wind in Southern hemisphere © 2011 Pearson Education, Inc.
  24. 24. Geostrophic Flow Ekman transport piles up water within subtropical gyres. Surface water flows downhill and to the right. Geostrophic flow – balance of Coriolis Effect and gravitational forces Ideal geostrophic flow Friction generates actual geostrophic flow © 2011 Pearson Education, Inc.
  25. 25. Western Intensification Top of hill of water displaced toward west due to Earth’s rotation Western boundary currents intensified in both hemispheres  Faster  Narrower  Deeper  Warm Coriolis Effect contributes to western intensification © 2011 Pearson Education, Inc.
  26. 26. Eastern Boundary Currents Eastern side of ocean basins Tend to have the opposite properties of Western Boundary Currents  Cold  Slow  Shallow  Wide © 2011 Pearson Education, Inc.
  27. 27. Eastern and Western Boundary Currents © 2011 Pearson Education, Inc.