1. Waves, Tides, and Currents
MOTION IN THE OCEAN
Waves, Tides, and Currents

2. Waves Up/Down movement of the surface of the ocean
Mostly caused by winds
(Also earthquakes, volcanoes, grav. pull)
a form of energy that moves across water

3. Waves Check What You THINK You Know wavelength, wave height, trough, crest1
_____2_____ 3 4

4. Check What You THINK You Know wavelength, wave height, trough, crest
What is the horizontal distance between crests ?
What is the lowest part of the wave?
What is the highest part of the wave?
What is the vertical distance between crest and trough?

5. 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

6. Wave period : time for 2 crests to pass fixed point (T) sec
Wave speed (C) : C = wavelength / T (m/s)
Wave steepness : H / wavelength

7. 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

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

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

10. How Waves Affect the Shore
Longshore Drift
As waves come ashore, water washes up the beach at an angle, carrying sand grains.
Gravity causes the water and the sand to run straight back down the beach slope

11. Barrier Islands
Barrier islands like the one’s that stretch along the coast of New Jersey are formed from deposition of sediments coming from N.J. rivers, and sand being deposited along the coastal side of the island by the longshore drift.
Because the wind and waves are constantly redistributing the sand these islands are not permanent.
They are constantly being reshaped.

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

13. Breakers As waves approach the shore, the water becomes shallower.
The bottom of the waves begin to touch the sloping ocean floor.
Friction between the ocean floor and the water causes the waves to
slow down.
As the speed of the wave slows down the shape of the wave begins to change
Near the shore wave length decreases and wave height increases.
When the wave reaches a certain height, the crest of the wave topples.

14. TSUNAMI not “TIDAL WAVE”
Caused by undersea earthquake, volcano or landslide
Wavelength = ~150 mi. /500 km
Wave height = 6” – 1’- Can NOT perceive in boat
Speed > 500 mph/800 km.h
Slows down to ~25 mph at shore;
water builds up to ~65+ ft, m

15. Tsunami Waves

16. Creation of a Tsunami

17. 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

18. 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

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

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

21. 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

22. 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

23. Spring vs. Neap Tides

24. 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

26. 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

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

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

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

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

32. 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

33. IMPORTANCE OF SURF. CURRENTS
NAVIGATION
MIGRATION
WEATHER

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

35. 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

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

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