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Earth’s Oceans

Earth’s Oceans. Part 5: Motion of the Ocean. Three Types of Motion. Waves Currents Tides. Waves. Pulses of energy that move through water Set in motion by: Wind (most commonly) Earthquakes The gravitational pull of the moon. Waves. View the following lesson on waves:

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Earth’s Oceans

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  1. Earth’s Oceans Part 5: Motion of the Ocean

  2. Three Types of Motion • Waves • Currents • Tides

  3. Waves • Pulses of energy that move through water • Set in motion by: • Wind (most commonly) • Earthquakes • The gravitational pull of the moon

  4. Waves View the following lesson on waves: http://oceanexplorer.noaa.gov/edu/learning/player/lesson09.html Photo credit: NOAA

  5. Waves Caused by Wind • Called surface waves • Wind transfers energy to the water as it moves over the ocean surface • The energy then moves through the water as a wave • The water moves up and down in a circular motion but does not move horizontally along the surface. • Height of these waves depends upon: • Wind speed • Length of time the wind blows • Distance the wind blows over the water Animation from http://www.onr.navy.mil/focus/ocean/motion/waves1.htm

  6. Characteristics of Waves • Crest – highest point • Trough – lowest point • Wavelength – horizontal distance between waves • Wave height – vertical distance between crest and trough (amplitude) • Wave period – time it take for one wavelength to pass a give point • Wave frequency – number of waves per unit of time Diagram from: http://www.onr.navy.mil/focus/ocean/motion/waves1.htm

  7. Wave Action • Swells – long, wide waves in the open ocean that are not very high • Near the shore, wavelength decreases, wave height increases and crests become more peaked • The slope of the shore determines how the waves break • Surf: the surging of the ocean waves on to the shore • Undertow: water flowing back to the ocean View animation: http://oceanexplorer.noaa.gov/edu/learning/player/lesson09/l9la1_a.html

  8. Tsunamis • Caused by sudden displacements in the sea floor (earthquakes), landslides, or volcanic activity • Resulting waves can be very tall (up to 35 m when they strike) • Can cause great damage and loss of life along the coast Animation from: http://www.tsunami.noaa.gov/tsunami_story.html The 12/26/2004 tsunami in the Indian Ocean killed over 230,000 people.

  9. Currents • Movement of ocean water in streams or rivers • Can flow for great distances • Can play a dominant role in determining the climate of a region • Caused by two factors: • Wind patterns • Differences in water density

  10. Surface Currents • Caused mainly by wind patterns • To depths of ~400 m • Video: http://svs.gsfc.nasa.gov/vis/a000000/a003800/a003827/prepetual_ocean_1080p30.mp4 • Circular motion • Clockwise in the Northern Hemisphere • Counterclockwise in the Southern Hemisphere (as with winds) • May be warm or cold, depending on where they originate

  11. Long Distance Surface Currents Generally west coasts have cold currents & east coasts have warm currents

  12. Long Distance Surface Currents Gulf Stream • About 150 km wide, up to 1,000 m deep, speed averages 6.4 km/h (4 mph) • Carries warm water from the southern tip of Florida north along the east coast of the US • Video http://www.teachersdomain.org/resource/ess05.sci.ess.watcyc.drifters/ • Interactive diagram of 25 major ocean currents http://www.srh.noaa.gov/jetstream/ocean/currents_max.htm

  13. Short Distance Surface Currents • Found near shorelines where waves hit at an angle • Longshore currents move parallel to the shoreline • Pick up sand and other materials and then deposit them in the water close to the shoreline forming a sandbar Sandbar off Long Island Coast Photo credit: David Shankbone, August 2006.

  14. Short Distance Surface Currents • If the current cuts through a sandbar, the resulting powerful, narrow, outflow back to the ocean is a rip current. • A rip current is a type of undertow. • As the sandbar is often underwater, rip currents are difficult to see and dangerous.

  15. Deep Currents • Caused by difference in density of water • Density affected by: • Temperature • Salinity • Colder, saltier water at the poles sinks to the depths of the ocean and then moves away from the poles. • Most flow in directions opposite that of surface currents Global Ocean Conveyor Belt. This collection of currents is responsible for the large-scale exchange of water masses in the ocean, including providing oxygen to the deep ocean. The entire circulation pattern takes ~2000 years.

  16. Upwelling • The rising of deep cold currents to the ocean surface • Occurs when winds blow parallel to the coastline • Carries nutrient rich waters to the surface to support high levels of seaweed and plankton growth. • These areas are the best fisheries. Areas of coastal upwelling in red.

  17. Tides Low Tide High Tide • Regular rise and fall of ocean water caused by gravitational attraction between the Earth, moon, and sun. • Most coastal locations experience two high tides and two low tides per day. High Tide Low Tide Reference: http://csep10.phys.utk.edu/astr161/lect/time/tides.html

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