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Ocean Currents

Ocean Currents. Why is Ocean Circulation Important?. Transport ~ 20% of latitudinal heat Equator to poles Transport nutrients and organisms Influences weather and climate Influences commerce. Ocean Currents. Surface Currents The upper 400 meters of the ocean (10%). Deep Water Currents

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Ocean Currents

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  1. Ocean Currents

  2. Why is Ocean Circulation Important? • Transport ~ 20% of latitudinal heat • Equator to poles • Transport nutrients and organisms • Influences weather and climate • Influences commerce

  3. Ocean Currents • Surface Currents • The upper 400 meters of the ocean (10%). • Deep Water Currents • Thermal currents (90%)

  4. Surface Currents • Forces • Solar Heating (temp, density) • Winds • Coriolis

  5. Wind-driven surface currents

  6. Wind-Driven and Density-Driven Currents • Wind-driven currents occur in the uppermost 100 m or less • Density differences causes by salinity and temperature produce very slow flows in deeper waters.

  7. Sailors have know about ocean currents for centuries Sailors have know that “rivers” 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.

  8. Ben Franklin and the Gulf Stream

  9. Matthew Fontaine Maury The first systematic study of currents was done by Maury based on logbooks in the US Navy’s Depot of Charts and Instruments. His charts and “Physical Geography of the Sea” assisted navigators worldwide. http://www.npg.si.edu/exh/brady/gallery/97gal.html

  10. Winds and surface water • Wind blowing over the ocean can move it due to frictional drag. • Waves create necessary roughness for wind to push the water into larger waves. • One “rule of thumb” 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)

  11. Top-down drag • Wind acts only on the surface water layer. • This layer will also drag the underlying water, but with less force. • This means that the lower water moves with less speed. • Direction of movement is also influenced by the Coriolis Effect (we will look at this later!!)

  12. Current Gyres • Gyres are large circular-moving loops of water • Five main gyres (one in each ocean basin): • North Pacific • South Pacific • North Atlantic • South Atlantic • Indian • Generally 4 currents in each gyre • Centered about 30o north or south latitude

  13. Pacific Ocean surface currents

  14. What do Nike shoes, rubber ducks, and hockey gloves have to do with currents?

  15. Lost at Sea

  16. Read through the worksheet and track the progress of the ducks on the map.

  17. North Pacific Subtropical Gyre • “Great Pacific Garbage Patch” • Estimate: 46,000 pieces of floating garbage/mi2.

  18. North Pacific Subtropical Gyre 135° to 155°W and 35° to 42°N

  19. North Pacific Subtropical Gyre 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

  20. Eddy • A circular movement of 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 • Rotates clockwise • Found on the landward side of the current • Cold core ring (cyclonic eddy) • Rotates counterclockwise • Forms on the ocean side of the current

  21. Sargasso Sea

  22. Upwelling Vertical movement of water () • Upwelling = movement of deep water to surface • Hoists cold, nutrient-rich water to surface • Produces high productivities and abundant marine life • Downwelling = movement of surface water down • Moves warm, nutrient-depleted surface water down • Not associated with high productivities or abundant marine life

  23. Langmuir Circulation

  24. Surface and Deep-Sea Current Interactions Unifying concept: “Global Ocean Conveyor Belt” http://seis.natsci.csulb.edu/rbehl/ConvBelt.htm

  25. Heat Transport by Currents • Surface currents play significant roles in transport heat energy from equatorial waters towards the poles • May serve as “heat sources” to cooler overlying air, “heat sinks” from warmer • Evaporation and condensation participate in latent heat exchanges

  26. Matter Transport and Surface Currents • Currents also involved with gas exchanges, especially O2 and CO2 • Nutrient exchanges important within surface waters (including outflow from continents) and deeper waters (upwelling and downwelling) • Pollution dispersal • Impact on fisheries and other resources

  27. Thermohaline Circulation Global ocean circulation that is driven by differences in the density of the sea water which is controlled by temperature and salinity.

  28. Thermohaline Circulation White sections represent warm surface currents. Purple sections represent deep cold currents

  29. Thermohaline Circulation What effect does global warming play in thermohaline circulation? http://www.youtube.com/v/MZbsMlr9WRI?version=3

  30. Thermohaline Circulation 1 2 3 4 Atmospheric and ocean temp Subtropical evaporation High latitude precipitation & runoff CO2 fossil fuel combustion North Atlantic regional cooling Deep water formation & thermohaline circulation Nordic seas salinity & deep convection Potential feedback of increased tropical salinity 6 5 Global climate interconnections

  31. Thermohaline circulation S Fig. 7.26

  32. P Conveyor-belt circulation • Combination deep ocean currents and surface currents “What goes around, comes around” - the time to complete a cycle (or the residence time in the deep ocean) is from 750-1,000 years. Fig. 7.27

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