1. Waves, Tides, and Currents
MOTION IN 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 Ecology 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. Rogue Waves Greater than twice the size of surrounding waves
Very unpredictable
often come unexpectedly from directions other than prevailing wind and waves
Often steep-sided with unusually deep troughs
Causes:
Constructive interference
swells pass through one another
their crests, troughs, and lengths sometimes coincide and reinforce each other
form unusually large, towering waves that quickly disappear
If the swells are travelling in the same direction, these mountainous waves may last for several minutes before subsiding
Focusing of wave energy
waves formed by a storm develop in a water current against the normal wave direction
tend to be longer lived

10. TSUNAMI “TIDAL WAVE”
Caused by undersea earthquake, landslide 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. Creation of a Tsunami

13. 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

14. 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

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

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

17. 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

18. 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

19. Spring vs. Neap Tides

20. 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

22. 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

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

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

26. Surface Ocean Currents
Broad, slow drifts; never cross equator
Wind generated; circular gyres
Surface Ocean Circulation
Images and videos

27. - N. Hemisphere – clockwise; Right
Coriolis Effect
- N. Hemisphere – clockwise; Right
- S. Hemisphere – counterclockwise; Left
Video

28. 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

29. IMPORTANCE OF SURF. CURRENTS
NAVIGATION
MIGRATION
WEATHER

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

31. 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

33. Upwelling

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

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