1. MOTION IN THE OCEAN
Waves and Tides

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. 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

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

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

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

8. Links/Videos Wave activity

10. TSUNAMI = “harbor wave” in Japanese
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

11. Tsunami Waves

12. Indian Ocean Tsunami 2004
Indian Ocean 2004
Global Impact
December 26, 2004
9+ magnitude earthquake
Indian plate slid under Burma Plate, off coast of Sumatra
dead
15,000 missing
2 million displaced

13. Tsunamis

14. 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

15. Tides are very long, slow waves
They have a wave period of 12 hours 25 min
Tidal day is 24 hours 50 min

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

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

18. Types of Tides 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
2x’s/month

19. 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

20. Spring vs. Neap Tides

21. 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

23. 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
Why different types of tides?

24. Types of Tides

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

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

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

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

30. 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

31. IMPORTANCE OF SURF. CURRENTS
NAVIGATION
MIGRATION
WEATHER

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

33. 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

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

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