1. Waves, Currents and Tides
Motions of the Ocean
Waves, Currents and Tides

3. I. General Info. 1. motion is needed for “mixing”
A. The ocean is in constant motion
1. motion is needed for “mixing”
2. replenishing of O2
3. “moving” of food
4. change in our weather
B. The three major motions are
1. Waves
2. Currents
3. Tides

4. *water usually moves in a circular motion B. Causes:
II. Waves
A. Waves – pulses of energy through the water = the water does NOT move
*water usually moves in a circular motion
B. Causes:
1. Wind = most waves are created from winds
2. Earthquakes
3. Volcanoes

5. 4. Underwater landslides
5. These create tsunamis = large waves of 35m = 75ft

6. WAVES

10. C. Size of a wave determined by:
1. The wind’s speed
2. Duration of wind = length of time wind blows
3. Fetch = distance wind blows without interruption

11. D. Sizes of wave
1. ripples = m, clam waters
2. moderate = .6 – 1m (1 – 3ft.); mild seas
3. medium = 1 – 2m (3 – 8ft.), rough seas or whitecaps
4. high = 4 – 9m (13-30ft.), high seas
5. towering waves = 35m +, hurricane (typhoon)

14. E. Parts of a Wave
1. Crest – highest point of wave
2. Trough – lowest point of a wave
3. Wave length – distance between two consecutive crests
4. Wave height – distance between a crest & a trough
5. Wave period – time it takes for two consecutive crest to pass a fixed point

15. Crest
Wavelength
Wave height
Trough

16. 6. Can calculate speed of the wave:
a. wave length/wave period = wave speed or L/T = C
b. wave length of 20m & wave period of 4sec = 5m/sec
c. so, can also calculate length & period
7. This helps to determine navigation, hurricane power, etc

18. F. Life of a Wave
1. Energy is transferred from the wind to the water (earthquakes, etc)
2. A constant wave is generated, not very high, but very long = swell
*the water doesn’t move forward, the energy does
*creating wave after wave

20. 3. Wave moves closer to shore
*waves also move downward, but loses energy the deeper it goes
4. L (wave length) decreases; H (wave height) increases
5. Wave crashes forwards = breaker
* waves break about 1.3 X H (wave height)

21. 6. Wave surges onto shore = surf
7. Water flows back into ocean = undertow; carrying pebbles & sand with it
*undertows can be very dangerous; very strong retreating water,
lasting several km

23. G. Types of Breakers
1. Plunging breaker – form tubes or curls
a. high speed
b. need steep, sloping bottom
c. can be dangerous = pounds downward, trapping people

26. 2. Spilling breakers – has line of tumbling foam
a. longest ride for surfer
b. needs a gentle sloping bottom

28. 3. Surging breakers – walls of white water
a. large wave suddenly hits bottom
b. causes great damage; tsunami

30. H. Importance of waves
1. Replenishes O2
2. Brings in food
3. Erodes beaches
4. Depositional activity (deposits sand)

31. III. Currents A. Currents = streams of moving water B. History
1. 1st studied in detail by Benjamin Franklin in 1777
2. In 1855, Maury made accurate charts of the major currents
3. Today, 100s of currents now known

32. 4. Many currents are constant
C. Causes
1. Wind patterns – set wind patterns create set currents
2. Rotation of Earth & Coriolis Force
3. Differences in water densities & T0
4. Drag of Earth’s rotation

35. D. Wind Patterns
1. Creates surface currents – depth of several 100m
a. T0 of current depends on origin
b. Types of surface currents
1) long distance surface currents – travel for 1000’s of km
a) very constant & predictable

38. b) Ex. Gulf Stream Current –. 150km wide, from Gulf of
b) Ex. Gulf Stream Current – 150km wide, from Gulf of Mexico to the top of Canada
2)Short distance surface current – travels short distances
a) usually travels close to shore
b) narrow, but can be very strong

39. 3. Longshore currents – runs parallel to the shoreline
a. current of fast moving water
b. creates rip currents – acts as an undertow
1) not usually dangerous
2) short lived
3) 2 longshore currents run into each other

41. 4) look for area with no breaking waves or
5) lighter waters
4. Eddies – circular motion of water on surface
a. can be dangerous
b. drags downward

45. E. Earth’s Rotation and Coriolis Force
1. Creates surfaces and deep sea currents
2. Also causes surface currents to move faster
3. And deep currents to move slower

46. 2. Coriolis force – forces that deflect water masses
a. In Northern Hemisphere – currents deflected to the right
b. In Southern Hemisphere – currents deflected to left
c. This allows for a predictable motion – giving us “current patterns”

48. 3. These two causes allow for a “well- mixed” ocean.
a. surface currents flow in opposite direction of deep currents
b. causes a change in T0
c. mixes ocean from top to bottom

49. F. Differences in Water Density
1. Causes deep currents
2. Cold water is more dense = sinks
3. Warm water is less dense = rises
4. High salinity water is more dense = sinks
5. Deep currents flow in opposite directions of surface currents
6. Helps mix ocean from top to bottom

51. Agulhas Current
Indian
Warm
Alaska Current
North Pacific
Benguela Current
South Atlantic
Warm/Cool
Brazil Current
California Current
Cool
Canaries Current
N. Atlantic

52. East Australian Current
South Pacific
Warm
Equitorial Current
Pacific
Gulf Stream
North Altantic
Warm
Humboldt (Peru) Current
South Pacific
Cool
Kuroshio (Japan) Current
North Pacific
Labrador Current
North Atlantic

53. North Atlantic Drift
North Atlantic
Warm
North Pacific Drift
North Pacific
Oyashio (Kamchatka) Current
Cool
West Australian Current
Indian
West Wind Drift
South Pacific

55. G. Upwelling
1. Most important current in the ocean
2. upwelling – a nutrient rich deep current that is forced to the surface
3. brings all kinds of food, nutrients, etc
4. makes for very rich fishing ground
5. Created when a deep current is forced to surface

59. H. Importance of Currents
1. Alters Earth’s surface T0
2. Circulates ocean
3. Helps shape our shoreline by erosional & depositional activity
4. Creates upwellings = very important to organisms

60. IV. Tides A. Tides = Periodic rise and fall of the level of the ocean
B. Causes
1. Alignment of the sun, moon, & earth
2. Gravitational pull of sun & moon
3. Centrifugal force – force that pushes “objects” away from center of rotation

63. C. Types of Tides
1. High tide – when sea level has risen
2. Low tide – when sea level is low
3. Ebb tide – outgoing tide, between the high & low tides
4. Flood tide – incoming water, between low & high tide

64. 5. Spring tides – very strong tides; very high & very low tides
a. Last 7 days
b. Occur every 14 days
6. Neap tides – very weak tides; not very high or low

68. 7. Mixed tides – not as strong or as weak as others
a. occur between spring & neap tides
b. occur every 14 days
c. last 7 days

70. D. When Tides Occur
1. Diurnal tides – have one low tide & one high tide in 24 hr.
2. Semidiurnal tides – two high tides & two low tides in 24 hr.

73. E. What Determines Type of Tides
1. Sun, Moon & Earth in a straight line causes spring tides
a. gravitational pull on Earth created by Sun & Moon causes a “bulge”
b. centrifugal force creates a “bulge” on the other sides
c. Full Moon & New Moon gives us the highest tides

75. F. Sun, Moon & Earth in a 90 causes neap tides
a. gravitational pull is balanced
b. centrifugal force is cancelled out by places of Sun & Moon

79. G. Importance of Tides
1. Tides shape the shoreline by erosion
2. Tides create completely new ecosystems
3. Tides are a good source for generating electricity
4. Some areas have extremely forceful tides