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MOTION IN THE OCEAN

MOTION IN THE OCEAN. Waves, Tides, and Currents. Waves. A disturbance which moves through or over the surface of a fluid Mostly caused by winds (Also earthquakes, volcanoes, grav. pull) Form of great energy. Wave Characteristics. Parts of a Wave Crest = high point

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MOTION IN THE OCEAN

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  1. MOTIONIN THE OCEAN Waves, Tides, and Currents

  2. Waves • A disturbance which moves through or over the surface of a fluid • Mostly caused by winds (Also earthquakes, volcanoes, grav. pull) • Form of great energy

  3. Wave Characteristics • Parts of a Wave • Crest = high point • Trough = low point • Height = vertical distance from crest to trough • Wavelength = Horizontal distance between crest to crest or trough to trough

  4. Wave period : time for 2 crests to pass fixed point (T) sec Wave speed (C) : C = wavelength / T (m/s) Wave steepness : H / wavelength When H / wavelength = 1/7 or angle at crest 120 or less = Breaker

  5. Size of Wind Generated Waves • Depends on 3 things: • Wind Speed • Wind Duration (length of time wind blows) • “Fetch” Extent of open water across which the wind can blow

  6. Water Motion in Waves • Water travels in vertical circular orbits • Wave moves, particles don’t!

  7. Importance of Waves • Shaping Coastlines • Erode cliffs • Grind rock into sand • Ecology • Returns O2 to water • Stir up food for filter feeders

  8. Types of Waves CHOP – Short period (back bays) SWELL – Long period (boat rolls; seasickness) SWASH – water up beach BACKWASH – back down

  9. TSUNAMI “TIDAL WAVE” Caused by undersea quake or volcano • Wavelength = ~150 mi. Wave height = 6” – 1’ • Can NOT perceive in boat Speed > 500 mph Slows down to ~25 mph at shore; water builds up to ~65+ ft

  10. Tsunami Waves

  11. Creation of a Tsunami

  12. Tides The rhythmic rise and fall of the ocean’s water • High tide = rising, incoming tide, flow • Low tide = receding, outgoing tide, ebb • Slack tide = vertical movement stops

  13. Tides are very long, slow waves • They have a wave period of 12 hours 25 min • Tidal day is 24 hours 50 min • NJ has 2 high and 2 low tides daily

  14. 1. Gravitational pull of sun & moon on Earth What Causes Tides? • Moon closer, therefore > effect • Like magnet, pulls water away from surface = TIDAL BULGE

  15. 2. Centrifugal Forces • Bulge on opposite side because centr. force > pull of moon • Produced by motions of Earth, sun, & moon

  16. Types of Tides 2x’s/month • Spring Tide • - Moon and sun are in direct line with one another - Results in unusually high tidal range • Tidal Range = vertical distance between high & low tides

  17. Neap Tide sun and moon are at right angles Pulls cancel each other out – causes a weak pull unusually low tidal range 2 x’s / month

  18. Spring vs. Neap Tides

  19. Distance bet. Moon & Earth Perigee Tides Moon closest to earth, very high tides (causes flooding) Apogee Tides Moon farthest away from earth, very low tides

  20. Types of Tides Continued • Diurnal Tides • 1 high & 1 low / day • Parts of Gulf of Mexico and Asia • Semi-Diurnal Tides • 2 high & 2 low / day • Atlantic coasts of North America and Europe • Mixed • 2 high & 2 low / day (height varies) • Pacific coast

  21. Importance of Tides • Expose & submerge orgs • Circulate water in bays & estuaries • Circulates food, wastes, etc • Trigger spawning (grunion, horseshoe crab)

  22. Currents • What are currents? - “Rivers” of circulating water • Causes - Wind - Rotating Earth - Density Changes

  23. Surface Ocean Currents • Broad, slow drifts; never cross equator • Wind generated; circular gyres

  24. Coriolis Effect - N. Hemis – clockwise; Right - S. Hemis – counterclockwise; Left

  25. Gulf Stream - N. Atlantic - Brings warm water from equator north along east coast of N. A. • Sometimes form eddies – circulating water that pinches off from the current

  26. IMPORTANCE OF SURF. CURRENTS NAVIGATION MIGRATION WEATHER

  27. Localized Surface Currents Longshore Current. Flows parallel to shore; move sediment

  28. RIP CURRENT - Caused by converging longshore currents - Very dangerous ; Red Flag - DO NOT fight rip current; swim parallel to shore to get out of channel

  29. Deep Ocean Currents Separated from surface currents by boundary called a “Thermohaline” (diff in densities) • Flow beneath surface; cross equator • Move North to South

  30. Importance Of Deep Currents • Upwelling • Brings deep water to surf. • Circulates nutrients up • Moves plankton & larvae

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