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Part 5: Motion of the Ocean

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Presentation on theme: "Part 5: Motion of the Ocean"— Presentation transcript:

1 Part 5: Motion of the Ocean
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: Photo credit: NOAA

5 Waves Caused by Wind Height of these waves depends upon:
Wind speed Length of time the wind blows Distance the wind blows over the water 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. Animation from

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:

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:

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: 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: 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 Interactive diagram of 25 major ocean currents

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:


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