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Ocean Currents

Ocean Currents . Earth Science . Ocean Currents . Currents- water in a stream Surface currents- currents that move on or near the surface & are caused by wind Deep current- move very slowly beneath the surface of the ocean & are caused by density differences in water .

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Ocean Currents

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  1. Ocean Currents Earth Science

  2. Ocean Currents • Currents- water in a stream • Surface currents- currents that move on or near the surface & are caused by wind • Deep current- move very slowly beneath the surface of the ocean & are caused by density differences in water

  3. Ocean Currents: Surface Currents • Driving energy source for surface currents is wind • Surface currents extend down to a depth of 100m • 3 controlling factors in surface currents • Wind belts • Earth’s rotational effects • Location of the continents

  4. Ocean Currents: Surface Currents • Wind belts • Most directly affect the surface currents • Trade winds & westerlies • Trade winds at latitudes north & south of the equator • Westerlies are located in the middle latitudes • North of the equator the trade winds blow from the northeast (Northern Hemisphere) & are usually warm • Southern Hemisphere trade winds blow from the south east • In both hemispheres they push water to the west

  5. Wind Belts • Northern Hemisphere westerlies blow from the southwest…moves currents eastward across the Atlantic & Pacific Oceans • Southern Hemisphere westerlies blow from the northwest…moves currents eastward • Produce the largest current on earth…West Wind Drift • Travels the entire circumference of the earth and is located in the southern part of all 3 major oceans

  6. Ocean Currents: Surface Currents • Coriolis Effect • Deflection of the earth’s winds and ocean currents based on the rotation of earth • Coriolis effect along with the earth’s winds cause gyres • Gyres- huge circle of moving water • Northern hemisphere- gyre moves clockwise • Southern hemisphere- gyre moves counterclockwise

  7. Ocean Currents: Surface Currents • Continents • The surface current flows against a landmass and is divided and deflected • Equatorial Current • Warm currents • 2 of them both move in a westward direction

  8. Ocean Currents: Surface Currents • North Pacific & Atlantic Currents • North Atlantic • North Atlantic Equatorial Current • Warm current that moves water north along the east coast of North America called the Gulf Stream • Gulf Stream widens & slows and becomes the North Atlantic Drift • Drift- weak current • All of those currents form the North Atlantic Gyre

  9. Ocean Current: Surface Currents • North Pacific • Similar to the North Atlantic • Japan Current is equivalent to the Gulf Stream • Flows northward & turns into the North Pacific Drift when it spreads out & slows down as it flows towards North America

  10. Ocean Currents: Surface Currents • Currents in the Southern Hemisphere • Currents here also flow in gyres but in a counterclockwise direction • Southern regions of all three major oceans constant westward winds produce the West Wind Drift • West Wind Drift is the largest current in the world • Because there is no continents to stop it the West wind drift completely circles Antarctica

  11. Ocean Currents: Surface Currents • Currents in the Southern Hemisphere cont… • Indian Ocean currents follow 2 patterns • Southern part the currents follow a counterclockwise gyre • Northern part the currents are governed by monsoons • Monsoons change directions with the seasons

  12. Ocean Currents: Deep Currents • Cold, dense currents that flow beneath the surface of the ocean • Much slower moving than surface currents • Produced as cold, dense water of the polar regions sinks & flows beneath warmer ocean water toward the equator • Movements are the result of density differences • Higher density of polar waters is also a result of an increase in salinity • Deep-current layer rises only when winds blow the surface water out of the way

  13. Ocean Currents: Deep Currents • Antarctic Bottom Water • The densest & coldest ocean water in the world • Dense, cold water sinks to the bottom & very slowly move north forming the Antarctic Bottom Water current • Moves to north to about 40 degrees & takes several hundred years to make the trip

  14. Ocean Currents: Deep Currents • North Atlantic Deep Water • South of Greenland the water is exceptionally cold & has high salinity causing it to sink • Forms a current that travels south underneath the Gulf Stream • Flows southward all the way to the Antarctic & over the Antarctic Bottom Water • Deep Atlantic currents also are found near the Mediterranean Sea

  15. Ocean Currents: Deep Currents • Turbidity Currents • Occur when large masses of sediment that have accumulated along a continental shelf or continental slope suddenly break loose and slide downward • Causes the water to become more dense than the surrounding water • Believed to cause submarine canyons to deepen

  16. Ocean Waves • Wave- periodic up and down movement of water • Transfer energy • 2 basic parts of a wave: • Crest- highest point of a wave • Trough- lowest point of a wave • Wave characteristics • Wave height- vertical distance between a crest & a trough of a wave • Wavelength- horizontal distance between 2 crests of a wave • Wave period- time it takes for one complete wavelength • Wave speed= wavelength/period

  17. Ocean Waves • Wave Energy • Main source of energy for waves is wind • The more energy that is transferred the larger the wave becomes • Because of surface area… • Large waves tend to become larger because the wind has more area to push on • Smaller waves tend to die out because there is a very small surface area for the wind to push on • Swell- group of long, rolling waves that are the same size

  18. Ocean Waves • Water Movement in A Wave • Only the energy of wave moves forward, the water itself moves very little • The water particles within the wave move in a circular motion • Circle traced by each water particle in a wave has a diameter equal to the height of the wave • Energy received by a wave decreases as depth increases because the waves receive their energy from the wind • Diameter of the circle traced by each water particle decreases as depth increases

  19. Ocean Waves • Wave Size • 3 factors that affect wave size: • Speed of the wind • Length of time the wind blows • Fetch of a wave • Distance that the wind can blow across open water • Long fetch produces very large waves • Likely to occur during storms • Size of a wave will only increase to a certain height to length ratio before it collapses • Whitecaps- occur when high wind speeds blow the crest off of a wave

  20. Ocean Waves: Waves & the Shore • Breakers • Height of a wave changes as the wave approaches the shore • As a wave moves into shallow water, the bottom of the wave is slowed by friction but the top of the wave continues to move at its original speed • The top of wave gets farther & farther ahead of the bottom & eventually it topples over & forms a breaker. • Height of the wave when it topples over is one to two time the height of the original wave

  21. Ocean Waves: Waves & the Shore • Breakers cont… • Size & force of breakers are determined: • Original wave height • Wavelength • Steepness of the ocean floor close to shore • More steep = rapid increase of wave height = breaker with greater force • Pacific Coast • Less steep = slower increase of wave height = breaker with less force • Atlantic Coast

  22. Ocean Waves: Waves & the Shore • Undertows & Rip Currents • Undertow- water carried onto a beach is pulled back into deeper water by an irregular current • Create problems only along shores with steep drop-offs • Rip current- form when water from large breakers returns to the ocean through channels in underwater sand bars that are parallel to the beach • Flow perpendicular to shore

  23. Ocean Waves: Waves & the Shore • Longshore Currents • Form sandbars • Forms as waves approach the beach at an angle • Flow parallel to the shore

  24. Ocean Waves: Wave & the Shore • Tsunamis • Most destructive waves in the ocean • Energy that forms them comes from seismic sea waves not the wind • Usually caused by earthquakes on the ocean floor, but also by volcanic eruptions & underwater landslides • Have very long wavelength, wave period is about 15 minutes, and speed of 725 km/hr • Entire depth of the water is involved in wave motion • Height increase greatly as they approach shore

  25. Tides • Tides- daily changes in the level of the ocean surface • The gravitational pull of the moon on the earth and its waters is the major cause of tides • Low tides are formed halfway between two high tides

  26. Tides: Behavior • Tidal movement is due to the rotation of the earth and the pull of the moon. • Earth rotates from west to east, so tidal bulges appear to move westward around the earth. • Because there are two tidal bulges most locations on the ocean have two high tides & two low tides • Tidal range- difference in the level of high tide and low tide at specific locations • Can vary widely from place to place

  27. Tides: Behavior • During period of new moon & full moon the high tides are the highest and the low tides the lowest • This is because the sun, moon, & earth are all aligned • These are called spring tides • During 1st quarter & 3rd quarter phases the daily tidal range is the smallest • This is because the moon & the sun are at right angles to each other in relation to the earth • These tides are called neap tides

  28. Tides: Variations • Tidal patterns are greatly influenced by the size, shape, depth, & location. • Atlantic Coast: tides are semidiurnal, which means twice a day • Have a fairly regular tidal range • Gulf of Mexico: diurnal, which means once a daily • Pacific Coast: follow a mixed pattern & have an irregular tidal range • Very high followed by very low, then a lower high tide followed by a higher low tide

  29. Tides: Variations • Tidal oscillations- caused by the slow rocking motions of ocean water that occur as the tidal bulges move around the ocean basins • Produce the world’s greatest tidal range in the Bay of Fundy (tidal ranges is larger than 15m)

  30. Tides: Tidal Currents • Tidal current- occurs as the ocean water rises and falls with the tides, it flows toward & away from the coast. • Flood tide- when tidal current flows toward the coast • Ebb tide- when tidal current flows away from the coast • Slack water- time between flood tide and ebb tide with no tidal currents. • Tidal bore- surge of water that rushes upstream where a river meets an ocean

  31. Tide Videos • http://youtu.be/kJOvxQElfLc • http://youtu.be/5W2sM1Ma7YA

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