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  1. 1. Chapter 8 and 9
  2. 2. How can density drive circulation?  Temperature, salinity, and temperature changes  Well mixed surface layer of 100 m and below that density changes rapidly  Due to temperature decreases (100- 1000 m)  Below 1000 m changes are not as great  Density increases as head toward bottom of ocean
  3. 3. Latitude affects density  Warm low-salinity water at equator less dense than  30 degrees where water cooler and higher salinity due to lack of rain  60 degrees is even more dense than equator and 30 degrees N. or S. due to temperature and salinity  Polar regions in winter when sea ice is formed have higher salinity and dense water sinks below all other latitudes
  4. 4. What is thermohaline circulation? How is it driven?  Density driven vertical circulation controlled by temperature and salinity  If more dense water on top then initiates downwelling  While less dense water rises called upwelling = overturn
  5. 5. Thermohaline Circulation
  6. 6. NASA Imagery
  7. 7. Thermohaline Circulation  If same density in water column then waves and wind can mix easily  If density changes with depth then does not over turn and more stable  Large scale thermohaline circulation system ensures eventual mixing from top to bottom  Seasonal changes in temperature more important than seasonal changes in salinity in altering density in open oceans
  8. 8. What are the layers dividing?  Temperature, salinity, and density  North Atlantic Ocean Deep Water = where converge at 60 degrees N.  What is the result of this convergence?  34 0/00 and 2-4 degrees C  Dense water sinks and moves south  Above very salty warm water is trapped by gyre movement  Between these layers is an intermediate salinity and temperature  Mediterranean water finds own layer as empties into ocean  Antarctic Intermediate water is warmer and less salty than the Atlantic Ocean Deep Water
  9. 9. Subsurface layers in Atlantic
  10. 10. Sea Ice forms Antarctic Bottom water and is the densest water in the ocean  Sea Ice forms Antarctic Bottom water and is the densest water in the ocean  This water moves northward and under the Atlantic Deep water  Trapped on the West side of the Mid- Atlantic Ridge system  Moves as far North as equator  North Atlantic Deep water splits as reaches surface and northward part becomes South Atlantic surface water and Antarctic Intermediate water and moves southward
  11. 11. What differences do you notice between the different oceans?  Pacific Ocean colder less salty water  Atlantic warmer and more salty  The Arctic Ocean = density controlled by salinity and not temperature  Combines with Gulf Stream water to form North Atlantic Deep water  The Pacific Ocean = Conditions uniform below 2000 m  N. Pacific isolated from the Arctic Ocean  Western side cold Bering Sea water converges with Equatorial currents produces a small volume that sinks to mid depths  Indian Ocean = Antarctic circumpolar water mainly and small amounts of Antarctic Intermediate water and warm salty surface water
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  13. 13. What is a gyre?  Circular motion of larger ocean currents  Currents driven by trade winds and Coriolis effect accumulate in the middle of the gyre and elevate water 3ft or more  Western Intensification western sides of gyres are narrower and more intense
  14. 14. Gyres  Western sides more intense due to = increased coriolis effect with increased latitudes, changing wind direction with latitude, friction between ocean currents and land masses  Most intense in N. Hemisphere with Gulf Stream and Kuroshio Currents  Others obscured by deflection currents or islands
  15. 15. Surface currents driven by?  The Pacific Ocean  Trade winds move water away from Central & S. Am. and push up against Asia  Westerlies move water away from Asia and push up against west coast of N. Am.  Water that accumulates must move towards water that has been removed  Creating CA and Kuroshio currents on E. and W. sides  Note other minor currents that feed into the N. Pacific Gyre (i.e. Oyashio
  16. 16.  Gyres are on 5 degrees either side of equator and Equatorial Countercurrent runs in the opposite direction (i.e. helps return surface water that has accumulated against Asia)  Charts can show surface flows over specific time but do not reflect  El nino and la nina
  17. 17. The Atlantic Ocean  Gulf Stream fed by both N. Equatorial and Gulf currents  Speeds up to 5ft per second  Volume flow 500x the Amazon River  FL current may exceed Gulf Stream in speed  N. Atlantic Gyre isolates Sargasso Sea  1000 m deep of clear warm surface water  Defined by the currents and N. Atlantic Ridge  Sargasso seaweed or algae provides rich community in a dessert of open ocean (with down welling = nutrient poor)
  18. 18. _world_map.png
  19. 19.  S. Atlantic Ocean trade winds move water to west but Brazil splits the S. Equatorial Current.  Most goes into Caribbean Sea and Gulf  Why is this important to the U.S.?
  20. 20. Cousteau and the Amazon  03545/  The Amazon feeds out into the ocean and flows North past the Caribbean Islands and into the Gulf of Mexico  What goes on in the Amazon affects us!
  21. 21. The Arctic Ocean  Large clockwise gyre  Some water from Pacific through Bering Strait  Some water from Atlantic west of Spitsbergen  West Greenland water flows S. and joins Labrador Current
  22. 22. Indian Ocean  The Indian Ocean  S. Hemisphere ocean  Smallest Gyre  N. Equatorial Current strengthened by northeast trade winds during dry season  Wet monsoon season winds strengthen the Equatorial Countercurrent and reduce N. Equatorial  This seasonal shift unlike in Atlantic or Pacific gyres
  23. 23. Convergent vs. Divergent  What is the difference between convergence and divergence currents?  Convergence = combining of currents where downwelling occurring  Divergence = currents upwell and move away from each other
  24. 24. Convergence Currents  Subtropical convergences at 30-40 degrees N. and S.  Arctic and Antarctic convergences at 50 degrees N. and S.  Three major ocean divergence zones = two tropical and one Antarctic Convergence brings oxygen rich surface water to depths and
  25. 25. Divergence brings nutrients up from the deeper waters  Mixing of waters of different geographic regions mix with these currents Thermohaline and wind driven currents are closely related  Changing sea levels, moving continents, and shapes of ocean basins have changed these currents  Climate change also has altered locations and role of upwelling and down welling  Surface currents driven by winds and thermohaline help redistribute heat, salinity, and dissolved gases
  26. 26. Coastal Upwelling and Downwelling  Why are these area important?  Productive areas for nutrients and fish  Trade winds on Western sides of continents create continual upwelling  Seasonal upwelling and downwelling occurs along coast lines  Lack of land in S. Hemisphere has less of this affect
  27. 27. Northwest U.S.  From S. CA to Vancouver Island Southerly winds in winter and Northerly in summer and thus changing Ekman transport of water  Net result is upwelling in the summer and downwelling in the winter
  28. 28. globecpne.html
  29. 29.  What is the Ekman Spiral and Ekman Transport?  Deeper water moves more slowly with greater deflection and water at the bottom moves in the opposite direction (i.e. spiral motion)
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  31. 31. Eddies  Where are they found and how are they created?  Pockets of cold or warm water moving in a circular motion spinning off major current (i.e. Gulf Stream)  Current meanders and creates these pockets on either side  Eddies occur throughout the ocean at all depths  Each eddy has own chemistry until it mixes with surrounding water
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  33. 33. Fish and other marine life use Eddies to escape predators in the open ocean! (Gulf Stream below)
  34. 34. How are currents measured?  Following the water with die, pictures or a machine  Also measure speed and direction as passes a fixed point  Satellite images  Buoys  Doppler  Could be used on the surface or underwater anchored to buoy
  35. 35. Image of acoustic doppler being used in Greenland
  36. 36.  Newer electronic meters emit narrow frequency sound beams in all four directions  Echo frequency is related to water speed and is known as the Doppler Effect  In order to emit frequency in all four directions, meter is checked against internal compass  Data can be stored or transmitted to ship or surface buoy
  37. 37. ml
  38. 38. How can oceans provide energy?  Through heat and currents  Oceans have large heat capacity  Ocean Thermal Energy Conversion (OTEC) works with temperature differences between surface and up to 1000 m
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  40. 40. Energy from Heat  Two types: 1) Closed system uses contained fluid such as ammonia or Freon with low boiling point or  2) Open system which directly converts sea water to steam
  41. 41.  Closed system = warm water passes over evaporator chamber that contains fluid. Working fluid is vaporized by heat from sea water. As vapor heats up it builds up pressure to spin turbine which in turn generates power. After fluid has been heated up then it is returned to liquid state to start cycle all over again.
  42. 42. Closed System
  43. 43.  Open system = requires large quantities of warm water and must be condensed by using fresh water.  Requires at least 20 degrees C difference between surface and depth in order to generate more power than is used
  44. 44. Open System
  45. 45. Hybrid System
  46. 46.  Latitudes of 25 degrees N. or S. would be best location for plants due to average sea temperature of 22 degrees C  Plant/Lab in Hawaii (NELHA) closed after seven years in use due to cost being 10x that of oil or coal  Now experimenting with bringing cold water from depths and producing fresh water with lab.
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  48. 48. Other sources of energy in the oceans…