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Section 3: Ocean Movements
Waves and currents drive the movements of ocean water and lead to the distribution of heat, salt, and nutrients from one region of the ocean to another. K What I Know W What I Want to Find Out L What I Learned
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Essential Questions What are the physical properties of waves?
How do tides form? What are the similarities and differences between various ocean currents? Ocean Movements Copyright © McGraw-Hill Education
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Vocabulary Review New prevailing westerlies wave crest trough breaker
tide spring tide neap tide surface current upwelling density current Ocean Movements Copyright © McGraw-Hill Education
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Waves A wave is a rhythmic movement that carries energy through space or matter—in this case, ocean water. Ocean waves are generated mainly by wind blowing over the water’s surface. Copyright © McGraw-Hill Education Ocean Movements
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Waves The highest point of a wave is the crest.
The lowest point is the trough. The vertical distance between crest and trough is the wave height, and the horizontal crest-to-crest distance is the wavelength. Wave speed increases with wavelength. Copyright © McGraw-Hill Education Ocean Movements
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Waves Concepts In Motion FPO Add link to Animation from p. 421 here. Ocean Movements Copyright © McGraw-Hill Education
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Waves Wave height Wave height depends on three factors: fetch, wind duration, and wind speed. Fetch refers to the expanse of water that the wind blows across. Ocean Movements Copyright © McGraw-Hill Education
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Waves Wave height The longer the wind can blow without being interrupted (wind duration) over a large area of water (fetch), the larger the waves will be. Also, the faster the wind blows (wind speed) for a longer period of time over the ocean, the larger the waves will be. Ocean Movements Copyright © McGraw-Hill Education
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Waves Breaking waves Collapsing waves are called breakers. A breaker forms when wavelength decreases and wave height increases as the wave nears the shore. Ocean Movements Copyright © McGraw-Hill Education
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Tides Tides are the periodic rise and fall of sea level.
The highest level to which water regularly rises is known as high tide, and the lowest level is called low tide. Ocean Movements Copyright © McGraw-Hill Education
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Tides Differences in topography and latitude cause three different daily tide cycles: semidiurnal, mixed, and diurnal. The tidal range varies from place to place. Ocean Movements Copyright © McGraw-Hill Education
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Tides The Moon’s influence
The Moon and Earth revolve around a common center of gravity and experience unbalanced gravitational forces. These forces cause tidal bulges on opposite sides of Earth. Ocean Movements Copyright © McGraw-Hill Education
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How are tides affected by phases of the Moon? Virtual Lab FPO Add link to Virtual Lab from ConnectED here. Ocean Movements Copyright © McGraw-Hill Education
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Tides The Sun’s influence
The gravitational attraction of the Sun and Earth’s orbital motion around the Sun influences tides. Lunar tides are more than twice as high as those caused by the Sun because the Moon is much closer to Earth. Ocean Movements Copyright © McGraw-Hill Education
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Tides The Sun’s influence
During a full or new moon, the Sun, the Moon, and Earth are all aligned. This causes solar tides to enhance lunar tides, causing high tides to be higher than normal and low tides to be lower than normal. These types of tides are called spring tides. Ocean Movements Copyright © McGraw-Hill Education
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Tides The Sun’s influence
A neap tide occurs during a first- or third-quarter moon, when the Sun, the Moon, and Earth form a right angle. When this occurs, solar tides diminish lunar tides, causing high tides to be lower and low tides to be higher than normal. Ocean Movements Copyright © McGraw-Hill Education
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Tides BrainPOP FPO Add link to BrainPOPfrom ConnectED here. Ocean Movements Copyright © McGraw-Hill Education
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Currents Currents at the surface of the ocean are usually generated by wind. Some currents are the result of tides. Deep-ocean currents usually result from differences in density between water masses. Ocean Movements Copyright © McGraw-Hill Education
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Currents Surface currents
Surface currents are wind-driven movements of ocean water that primarily affect the upper few hundred meters of the ocean. Surface currents follow predictable patterns and are driven by Earth’s global wind systems. Ocean Movements Copyright © McGraw-Hill Education
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Currents Gyres If Earth had no landmasses, the global ocean would have simple belts of easterly and westerly surface currents. Instead, the continents deflect ocean currents to the north and the south so that closed circular current systems, called gyres, develop. Ocean Movements Copyright © McGraw-Hill Education
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Currents Gyres There are five major gyres—the North Pacific, the North Atlantic, the South Pacific, the South Atlantic, and the Indian Ocean. Ocean Movements Copyright © McGraw-Hill Education
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Currents Upwelling The upward motion of ocean water is called upwelling. Upwelling occurs when surface water is moved offshore and deep, colder water rises to the surface to replace it. Ocean Movements Copyright © McGraw-Hill Education
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Currents Density currents
A density current is the movement of ocean water that occurs in depths too great to be affected by surface winds and is generated by differences in water temperature and salinity. Ocean Movements Copyright © McGraw-Hill Education
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Currents Density currents
Differences in salinity and temperature generate density currents in the deep ocean. Ocean Movements Copyright © McGraw-Hill Education
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Ocean Currents BrainPOP FPO Add link to BrainPOPfrom ConnectED here. Ocean Movements Copyright © McGraw-Hill Education
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Review Essential Questions Vocabulary
What are the physical properties of waves? How do tides form? What are the similarities and differences between various ocean currents? Vocabulary wave crest trough breaker tide spring tide neap tide surface current upwelling density current Ocean Movements Copyright © McGraw-Hill Education
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