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Ocean Currents

Ocean Currents. The Reality of Sending a Message in a Bottle. Why does the Ocean have waves? What are the parts of a wave? How does water move in a wave? What happens when a wave hits a beach?. ?. Define wave: . Wave – a rhythmic movement that carries energy through matter or space.

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Ocean Currents

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  1. Ocean Currents The Reality of Sending a Message in a Bottle

  2. Why does the Ocean have waves? What are the parts of a wave? How does water move in a wave? What happens when a wave hits a beach? ?

  3. Define wave: Wave – a rhythmic movement that carries energy through matter or space. in the ocean, waves move through seawater.

  4. Parts of a wave Wave height Wavelength Crest Crest Trough

  5. Parts of a wave: Crest – the highest part of a wave. Trough – the lowest part of a wave. Wavelength – the distance between two adjacent crests. Wave height – the vertical distance between the lowest part and the highest part.

  6. More wave words • Frequency – the number of complete waves (or oscillations) that occur over a given period of time. Usually measured in cycles per second. • Amplitude – half the wave height

  7. Most waves caused by wind Friction from the wind moving over the water causes the water to move along with the wind. If the wind speed is high enough, the water begins to pile up and a wave is formed.

  8. How does water move in a wave? Some clues: When you were at the beach, you probably noticed that the edge of the water goes back and forth with the waves. If you float an object on the ocean, it stays roughly in one place. It is not pushed forward by the waves.

  9. How water moves in a wave: At a depth about equal to half the wavelength, the motion stops. Particles of water move around in circles. The farther below the surface, the smaller the circle.

  10. At the beach: Wavelength decrease and wave height increases as waves approach the shore. Constant Wavelength Waves drag against the bottom and wave length decreases

  11. At the beach, part 2 As the wave slows, its crest and trough come closer together. The top of the wave is not slowed by friction and moves faster than the bottom. The top of the wave outruns the bottom and falls over. This collapsing wave is called a breaker.

  12. Ocean Current Layers • Surface Currents – upper 10% of the ocean; upper 400 m • Pycnocline – the layer between surface and deep waters; where a rapid change in temperature, salinity and density occur • Deep Current – lower 90% of the ocean

  13. Ocean Water Properties • How they impact ocean currents • Temperature – remember heat rises! • Salinity – remember salty water sinks! • Density – a function of temperature and salinity

  14. Ocean Surface Temperatures http://www.bigelow.org/shipmates/sstemp_lg.gif

  15. Temperature vs. Currents http://earth.usc.edu/~stott/Catalina/Oceans.html

  16. Ocean Surface Salinities http://www.bigelow.org/shipmates/salinity_lg.gif

  17. Ocean Density http://www.windows.ucar.edu/tour/link=/earth/Water/density.html&edu=high

  18. Primary Current Forces • These Start the Water MOVING: • Solar Heating • Winds • Gravity • Coriolis Force/Effect

  19. Current Forces Explained • Sun/solar heating - causes water to expand and move • Winds - push the water; winds blowing for 10 hrs across ocean will cause the surface water to flow @ ~2% wind speed; wind has the greatest effect on surface currents • Gravity - pull water downhill or pile against the pressure gradient (high/low); influences tides

  20. Winds http://www-earth.usc.edu/~stott/Catalina/Oceans.html

  21. Wind Driven Ocean Currents http://www.bigelow.org/shipmates/hc_currents_lg.gif

  22. Current Influences (cont’d) • Coriolis effect/force - Force due to the Earth's rotation, capable of generating currents. It causes moving bodies to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The "force" is proportional to the speed and latitude of the moving object. It is zero at the equator and maximum at the poles http://www.csc.noaa.gov/text/glossary.html • causes the water to move around the mound of water

  23. Surface Currents • Surface current – with surface circulation is less dense and influenced by winds • Warm surface currents: wind and Earth’s rotation • Cold surface currents: flow towards the equator • Upwelling current: cold, nutrient rich; result of wind • Western Boundary currents: warm & fast • Eastern Boundary currents: broad, slow, cool & shallow, associated with upwelling • Ex: Gulf Stream = surface current that is the upper 20% of the ocean, western boundary current

  24. Deep Currents • Deep water – cold, dense, salty; move by density forces and gravity; move slower than layers above • Thermohaline Circulation: is global ocean circulation. It is driven by differences in the density of the sea water which is controlled by temperature (thermal) and salinity (haline). In the North Atlantic it transports warm and salty water to the North. There the water is cooled and sinks into the deep ocean. This newly formed deep water is subsequently exported southward. This slow (~0.1 m/s), but giant circulation has a flow equal to about 100 Amazon Rivers. Together with the Gulf Stream it contributes to the comparatively warm sea surface temperature along the coast of western Europe and to the relative mild European winters. Once the water are in the deep, they remain there for up to 1000 years. http://www.climate.unibe.ch/~christof/div/fact4thc.html • Ex: Global Conveyer Belt = deep current that is the lower 20% of the ocean; takes 1,000 years to complete the cycle

  25. Global Conveyer Belt • Thermohaline circulation links the Earth's oceans. Cold, dense, salty water from the North Atlantic sinks into the deep and drives the circulation like a giant plunger. http://www.columbia.edu/cu/record/23/11/13.html Graphic - http://www.grida.no/climate/vital/32.htm

  26. Other Currents • Gyres – large mounds of water; large circular currents in the ocean basin • Ex: North Atlantic Gyre = consists of 4 separate currents – N. Equatorial, Gulf Stream, N. Atlantic Drift and Canary Currents

  27. Ocean Currents & Living Things • Currents are important to marine life as they help move food and nutrients making them available for photosynthesis, metabolic requirements and or consumption.

  28. OCEAN Motion Foldable(2 Tab Foldable) • Take your sheet of copy paper and fold it “Hamburger” style • Then fold the paper again “Hamberger” style • Look at my paper to make sure you’ve done it correctly before cutting.

  29. 4. Cut only the top sheet of paper at the fold line (creating 2 flaps covering the back of paper) Look at my example. Write Title on top flap “Causes of Ocean Motion” Write Title on other top flap “Effects of Ocean Motion”

  30. Under “Causes” Flapwrite 2 causes for each type of motion****USE PGS. 520-538 TO HELP Currents Waves

  31. Under “Effects” flapWrite at least 2 effects of the 4 different types of Ocean Motion • Surface Current: • Density Currents: • Waves: • Tides: ****USE PGS. 520-538 TO HELP

  32. Parts of a wave Wave height Wavelength Crest Crest Trough

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