1. MOTION IN THE
OCEAN
Waves, Tides, and Currents
Chapter 16.2

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

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

16. 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

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

21. 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

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

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

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

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

27. • 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

28. MIGRATION NAVIGATION
WEATHER

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

30. 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

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

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