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Ocean currents
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- 2. Why is OceanCirculation Important? ā¢ Transport ~ 20% of latitudinal heat ā Equator to poles ā¢ Transport nutrients and organisms ā¢ Influences weather and climate ā¢ Influences commerce
- 3. Non-rotating Earth Convection cell model
- 4. Add rotation andadd landmasses unequal heating and cooling of the Earth
- 5. Physical properties ofthe atmosphere: Density ā¢ Warm, low density air rises ā¢ Cool, high density air sinks ā¢ Creates circular- moving loop of air (convection cell)
- 6. Physical properties ofthe atmosphere: Water vapor ā¢ Cool air cannot hold much water vapor, so is typically dry ā¢ Warm air can hold more water vapor, so is typically moist ā¢ Water vapor decreases the density of air
- 7. Physical properties ofthe atmosphere: Pressure
- 8. 90o High pressure, dry climate 60o Low pressure, wet climate High pressure, dry climate 30o ITCZ intertropical 0o convergence zone= doldrums Low pressure, 30o wet climate 60o 90o
- 9. The Coriolis effect ā¢The Coriolis effect ā Is a result of Earthās rotation ā Causes moving objects to follow curved paths: ā¢ In Northern Hemisphere, curvature is to right ā¢ In Southern Hemisphere, curvature is to left ā Changes with latitude: ā¢ No Coriolis effect at Equator ā¢ Maximum Coriolis effect at poles
- 10. The Coriolis effecton Earth ā¢ As Earth rotates, different latitudes travel at different speeds ā¢ The change in speed with latitude causes the Coriolis effect
- 11. North Pole Buffalo moves 783 mph Quito moves 1036 mph Buffalo 15o Quito N Buffalo 79oW Quito South Pole
- 12. A) Idealized windsgenerated by pressure gradient and Coriolis Force. B) Actual wind patterns owing to land mass distribution..
- 13. Ocean Currents Surface Currents The upper 400 meters of the ocean (10%). Deep Water Currents Thermal currents (90%)
- 14. Surface Currents Forces 1. Solar Heating (temp, density) 2. Winds 3. Coriolis
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- 16. Wind-Driven and Density-Driven Currents ā¢ Wind-driven currents occur in the uppermost 100 m or less ā¢ Density differences causes by salinity and temperature produce very slow flows in deeper waters.
- 17. Sailors have knowabout ocean currents for centuries Sailors have know that āriversā flow in the seas since ancient times. They used them to shorten voyages, or were delayed by trying to stem them. If navigators do not correct to deflection by currents, they may be far away from where they think they are and meet disaster.
- 18. Ben Franklin andthe Gulf Stream
- 19. Matthew Fontaine Maury Thefirst systematic study of currents was done by Maury based on logbooks in the US Navyās Depot of Charts and Instruments. His charts and āPhysical Geography of the Seaā assisted navigators worldwide. http://www.npg.si.edu/exh/brady/gallery/97gal.html
- 20. Winds and surfacewater ā¢ Wind blowing over the ocean can move it due to frictional drag. ā¢ Waves create necessary roughness for wind to couple with water. ā¢ One ārule of thumbā holds that wind blowing for 12 hrs at 100 cm per sec will produce a 2 cm per sec current (about 2% of the wind speed)
- 21. Top-down drag ā¢ Windacts only on the surface water layer. ā¢ This layer will also drag the underlying water, but with less force. ā¢ Consequently, there is a diminution of speed downward. ā¢ Direction of movement is also influenced by the Coriolis Effect and Ekman Spiral
- 22. Ekman spiral Ekman spiraldescribes the speed and direction of flow of surface waters at various depths ā¢ Factors: ā Wind ā Coriolis effect
- 23. Ekman transport Ekman transportis the overall water movement due to Ekman spiral ā¢ Ideal transport is 90Āŗ from the wind ā¢ Transport direction depends on the hemisphere
- 24. Ekman Transport Water flowin the Northern hemisphere- 90o to the right of the wind direction Depth is important
- 25. Currents in theāRealā Ocean Currents rarely behave exactly as predicted by these theoretical explanations due to factors such as ā¢ Depthāshallow water does not permit full development of the Ekman spiral ā¢ Densityādeeper currents moving in different directions influence the overlying surface movement
- 26. Geostrophic Flow Surfacecurrents generally mirror average planetary atmospheric circulation patterns
- 27. Current Gyres Gyres arelarge circular-moving loops of water Five main gyres (one in each ocean basin): ā¢ North Pacific ā¢ South Pacific ā¢ North Atlantic ā¢ South Atlantic ā¢ Indian ā¢ Generally 4 currents in each gyre ā¢ Centered about 30o north or south latitude
- 28. Geostrophic flow andwestern intensification ā¢ Geostrophic flow causes a hill to form in subtropical gyres ā¢ The center of the gyre is shifted to the west because of Earthās rotation ā¢ Western boundary currents are intensified Figure 7-7
- 29. Western intensification of subtropical gyres ā¢ The western boundary currents of all subtropical gyres are: ā Fast ā Narrow ā Deep ā¢ Western boundary currents are also warm ā¢ Eastern boundary currents of subtropical gyres have opposite characteristics
- 30. Boundary Currents inthe Northern Hemisphere Type of Current General Features Speed Special Features Western boundary Currents warm swift sharp boundary Gulf Stream, Kuroshio narrow w/coastal circulation, deep little coastal upwelling Eastern Boundary Currents cold slow diffuse boundaries California, Canary broad separating from coastal shallow currents, coastal upwelling common
- 32. Pacific Ocean surfacecurrents
- 33. āHills and Valleysāin the Ocean balance between the ā¢ A Ekman transport and Coriolis effect produces āhillsā in the center of the gyres and āvalleysā elsewhere ā¢ Gravitational effects from sea floor features also produce variations in sea surface topography http://earth.usc.edu/~stott/Catalina/Oceans.html
- 34. What do Nikeshoes, rubber ducks, and hockey gloves have to do with currents?
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- 36. Duckie Progress ā¢January 1992- shipwrecked in the Pacific Ocean, off the coast of China ā¢November 1992 - half had drifted north to the Bering Sea and Alaska; the other half went south to Indonesia and Australia ā¢1995 to 2000 - spent five years in the Arctic ice floes, slowly working their way through the glaciers 2001 - the duckies bobbed over the place where the Titanic had sunk ā¢2003 - they were predicted to begin washing up onshore in New England, but only one was spotted in Maine ā¢2007 - a couple duckies and frogs were found on the beaches of Scotland and southwest England.
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- 38. North Pacific SubtropicalGyre ā¢ āGreat Pacific Garbage Patchā ā¢ Estimate: 46,000 pieces of floating garbage/mi2.
- 39. North Pacific SubtropicalGyre 135Ā° to 155Ā°W and 35Ā° to 42Ā°N
- 40. North Pacific SubtropicalGyre Great Pacific Garbage Patch- Good Morning America 2010 http://www.youtube.com/watch?v=uLrVCI4N67M&feature=player_embedded http://marinedebris.noaa.gov/info/patch.html#6
- 41. Eddy A circular movementof water formed along the edge of a permanent current In an average year, 10-15 rings are formed 150-300 km in diameter Speed 1 m/sec Warm core ring 1. Rotates clockwise 2. Found on the landward side of the current Cold core ring (cyclonic eddy) 1. Rotates counterclockwise 2. Forms on the ocean side of the current
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- 44. Upwelling and downwelling Verticalmovement of water (ļ) ā Upwelling = movement of deep water to surface ā¢ Hoists cold, nutrient-rich water to surface ā¢ Produces high productivities and abundant marine life ā Downwelling = movement of surface water down ā¢ Moves warm, nutrient-depleted surface water down ā¢ Not associated with high productivities or abundant marine life
- 45. upwelling downwelling
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- 47. Satellite Observations ā¢ TOPEX/Poseidon,Jason 1, and other satellites have observed patterns of change over the past few years ā¢ Animation of seasonal and climatically- influence shifts available at http://seawifs.gsfc.nasa.gov/OCEAN_PLANET/MOVIES /Topex_Dynamic_Ocean_Topography.mpg
- 48. El NiƱo-Southern Oscillation (ENSO) ā¢ El NiƱo = warm surface current in equatorial eastern Pacific that occurs periodically around Christmastime ā¢ Southern Oscillation = change in atmospheric pressure over Pacific Ocean accompanying El NiƱo ā¢ ENSO describes a combined oceanic- atmospheric disturbance
- 49. El NiƱo ā¢ Oceanicand atmospheric phenomenon in the Pacific Ocean ā¢ Occurs during December ā¢ 2 to 7 year cycle Sea Surface Temperature Atmospheric Winds Upwelling
- 50. Normal conditions inthe Pacific Ocean
- 51. El NiƱo conditions(ENSO warm phase)
- 52. La NiƱa conditions(ENSO cool phase; opposite of El NiƱo)
- 53. Non El NiƱo El NiƱo 1997
- 54. Non El NiƱo upwelling El NiƱo thermocline
- 55. El NiƱo eventsover the last 55 years El NiƱo warmings (red) and La NiƱa coolings (blue) since 1950. Source: NOAA Climate Diagnostics Center
- 56. World Wide Effectsof El NiƱo ā¢ Weather patterns ā¢ Marine Life ā¢ Economic resources El Nino Animation http://esminfo.prenhall.com/science/geoanimations/ani mations/26_NinoNina.html
- 57. Effects of severeEl NiƱos
- 58. Surface and Deep-SeaCurrent Interactions Unifying concept: āGlobal Ocean Conveyor Beltā http://seis.natsci.csulb.edu/rbehl/ConvBelt.htm
- 59. Heat Transport byCurrents ā¢ Surface currents play significant roles in transport heat energy from equatorial waters towards the poles ā¢ May serve as āheat sourcesā to cooler overlying air, āheat sinksā from warmer ā¢ Evaporation and condensation participate in latent heat exchanges
- 60. Matter Transport and Surface Currents ā¢ Currents also involved with gas exchanges, especially O2 and CO2 ā¢ Nutrient exchanges important within surface waters (including outflow from continents) and deeper waters (upwelling and downwelling) ā¢ Pollution dispersal ā¢ Impact on fisheries and other resources
- 61. Global ocean circulationthat is driven by differences in the density of the sea water which is controlled by temperature and salinity.
- 62. White sections representwarm surface currents. Purple sections represent deep cold currents
- 64. What effect doesglobal warming play in thermohaline circulation? http://www.youtube.com/v/MZbsMlr9WRI?version=3
- 65. 1 2 3 4 CO2 fossil fuel Atmospheric and Subtropical High latitude combustion ocean temp evaporation precipitation & runoff North Atlantic regional cooling Deep water formation Nordic seas & thermohaline salinity & deep Potential feedback circulation convection of increased tropical salinity 6 5 Global climate interconnections
- 66. Inquiry 1. What isa convection cell? 2. Which direction do currents get deflected in the Southern Hemisphere? 3. What depth should the water be for an Ekman spiral to occur? 4. How are surface currents created? 5. What is a gyre? 6. How can an El Nino impact upwelling? 7. Coriolis Effect is strongest near the _____?