Waves, Tides and Currents.

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

2. What is a Wave?
 A disturbance which
moves through or over
the surface of a fluid
 Caused most often by
winds, but also by
undersea earthquakes
and volcanoes.

3. What Waves Do
 Shape Coastlines
 Erode cliffs
 Grind rock into sand
 Build ‘cool’ structures
 Affect Organisms
 Return O2 to water
 Stir up food for filter
feeders
 Move organisms
Define: spit; sandbar, tombolo; sea stack; sea cave; sea arch

4. Wave Characteristics
Crest = high point
Trough = low point
Wave Height = vertical
distance from crest to trough
Wavelength = Horizontal
distance between crest to crest
or trough to trough
Amplitude = vertical
distance from still water level to
the crest or the trough

6. Wave period - Time in seconds for 2 crests to pass a fixed
point
Wave speed = Wavelength ÷ Time (m/s)
Wave steepness - Wave height ÷ wave length
More wave characteristics:

7. Wave Size
Depends on 3 things:
Wind Speed
Wind Duration (length of time wind blows)
“Fetch” - the extent of open water across which
the wind blows

8. Water Motion in Waves
 Water particles travel in
vertical circular orbits
 When a wave moves,
energy from the wind
moves through the water.
The water particles do not
move!

10. Types of Waves
 Capillary waves (Ripples) – smallest waves
 Whitecaps – a mixture of air and water on a
wave
 Swells – larger waves with a long period
(your boat rolls = seasickness!)
 Breakers – large waves that collapse onto
themselves
 Rogue waves – a large wave; very high crest
and low trough; can move rapidly; can cause
boats to capsize

11. Caused by undersea earthquake or volcano (seismic activity)
• Wavelength = ~150 mi.
• Speed > 500 mph
Slows down to ~25 mph at
shore; water builds up to >
65 feet
TSUNAMI - “TIDAL WAVE”

12. Waves and Coasts
Coasts are areas where the land meets the sea.
Coasts are shaped by the sea and the action of
waves – through the processes of:
•Transportation (movement of material up on to land and
back to sea – swash and backwash of waves)
•Deposition (leaving/dropping material on the coast; wave
swash is stronger than backwash)
•Erosion (wearing away of the coast; removing material;
backwash is stronger than swash)

13. Constructive & Destructive Waves
Constructive Waves:
•Operate in calm weather
•Lack much energy
•Crests are spaced apart
•Break on the shore;
deposit material on shore
and build beaches
(* Think about beachcombers)
Destructive Waves
•Formed by storms near
the coast
•Are powerful waves
•Crests are closely
spaced; producing a
swirling mass of water
•Cause erosion
[Go to: http://www.eleuthera-map.com/glass-
window-bridge-eleuthera.htm for information about
rogue waves at the Glass Window Bridge]

14. Marine Science –21st September 2017
Motion in the Oceans - Tides
Objectives:
After viewing and discussing a PPT,
students will be able to:
Define “tide”
Explain how tides are formed
Describe different types of tides
……..
(at least 75% accuracy expected on short-answer quiz)

15. Tides
 The daily rhythmic rise and fall of the ocean’s
water
High tide = rising tide; incoming tide; flow
Low tide = receding tide; outgoing tide; ebb
Slack tide (vertical movement stops)

16. 1. Gravitational pull of moon & sun on Earth
What Causes Tides?
Moon’s effect is greater, because it is nearer.
Like a magnet, moon pulls water away from earth’s surface = TIDAL BULGE
(Watch video)

18. What causes tides?
2. Centrifugal Force
• An outward pulling away
force from a rotating object
• Bulge on opposite side from
moon because centrifugal
force is greater than the pull
of the moon on that side.

19. Types of Tides
• Spring Tide
Moon and sun are in direct
line with one another
Results in unusually high
tides
Occurs 2 times per month at
full moon and new moon

20. Types of tides
• Neap Tide
 sun and moon are at right angles
 cancel each other out – causes a weak pull
 unusually low tides
 occurs 2 times per month

21. Spring Tides vs. Neap Tides

22. Types of Tides
 Diurnal Tides
 1 high tide & 1 low tide per day
 Parts of Gulf of Mexico and Asia
 Semi-Diurnal Tides
 2 high tides & 2 low tides per day
 Atlantic coasts of North America and Europe
(including the Bahamas)
 Mixed
 2 high & 2 low per day (height varies)
 Pacific coast
Note: The tidal day is approximately 24 hours and 50 mins.

24. Test Yourself
1. There are tidal bulges on opposite sides of the Earth.
2. In the Bahamas we have high tides and low tides every day.
3. The highest high tides are called tides.
4. What type of tide would be formed below?
1. What type of tide would be formed below?

25. Test Yourself (cont’d)
6. The force of pulls the moon and earth towards each other.
7. The is earth’s natural satellite. It takes about hours and minutes
to circle the earth.
8. Two places with extremely high tides are and .
9. Why would it be important for people to know when tides are high or low?

26. Homework
Research:
1. Which places on earth have extremely
high tides?
2. How are these extremely high tides used
to provide an alternative source of
energy?

27. More Tide Terms
Remember: The distance between the moon
and the earth affects the tides.
Perigee Tides
• Moon closer to earth (strong pull) = very high tides
(causes flooding)
Apogee Tides
• Moon further away from earth (weak pull) = very low tides
Earth
Moon
Moon
(About 220,000 miles) (About 253,000 miles)

28. Tidal Range
(The difference in height between low tide and high tide)

29. Factors that affect tidal range
 Slope of the sea floor
 Contours (shape) of the shore
 Depth of a channel
 Width of the entrance to a channel
 Friction between water and the sea floor
(Why are we not harnessing the power of tides in the Bahamas?)

30. Tidal Effects:
• Expose & submerge organisms
in the intertidal zone
• Circulate water in bays &
estuaries
• Trigger spawning (grunion,
horseshoe crab, sea turtles?)
• Circulates nutrients; circulates
wastes; moves objects up and
down on the beach.
• Useful in ship navigation in/out
of harbors

31. Ocean in Motion: Tides - Quick Quiz
1. By measuring the difference between high and low tide, we can find the______?
Ebb Current
Tidal Range
Diurnal Tide
2. Semi-diurnal tides occur . . .
Once a day
Only at mid-day
Twice a day
3. Tides occur at the same time each day.
True
False
4. What kind of tide occurs when the sun, moon and Earth are all in a straight line?
High Tide
Low Tide
Neap Tide
Spring Tide
5. Only the gravitational pull of the sun is important in creating tides.
True
False
6. A tidal day lasts for about 25 hours.
True
False
7. A ______ can be used to plot tidal information so that predictions can be made.
Tide gauge
Marigram
24-hr clock
8. Very high tides are useful in:
Producing energy
Washing away roads
Eroding beaches

32. Marine Science – 29/06/2017
Topic: Tides
Objectives:
After viewing a PPT and participating in a
discussion, students will be able to:
a.Construct a tide marigram
b.Use a marigram to predict future tides
*********
[Minimum 80% accuracy expected on the
marigram construction and tide predictions]

33. Using Tide Data - Marigrams
Can be used to predict high tides and low tides for weeks and
months ahead

34. Marine Science –21st September 2017
Topic: Oceans in Motion – Currents
Objectives:
After viewing a ppt presentation, and
discussion, students will be able to:
a. Define “current”
b. Describe the causes of currents
c. Differentiate between surface and
deep currents

35. Currents
• What is a current?
 A large volume of water flowing in a certain direction. Some
are circular, some move in an almost straight line (stream)
• Causes of currents:
• Wind
• Rotating Earth
(Coriolis Effect)
• Density Changes
• Temperature Changes
‘Crush’

37. Causes of Currents: An Explanation
 Sun/solar heating - causes water to expand
and move
 Winds - push the water. Winds blowing for 10
hours across ocean will cause the surface water
to flow at about 2% wind speed. Wind has the
greatest effect on surface currents
 Coriolis effect/force - Force due to the Earth's
rotation, capable of generating currents. It
causes it to be deflected to the right in the
Northern Hemisphere and to the left in the
Southern Hemisphere. It causes water to move
around the mounds of land.

39. Wind Driven Ocean Currents
Currents moving towards the poles are warm; currents moving towards the equator
are cold. Surface ocean currents are driven by global winds and play an important
role in redistributing heat around the globe. They influence the climate of the entire
planet.

40. Major Ocean Currents
Note: Currents flow at different velocities. Currents on the eastern side of
continents are faster than those on the western side. Thus the Brazilian
current is faster than the Humboldt current.

41. Gulf Stream
- Brings warm water
from equator north
along east coast of
North America
- Affects the islands of
the Bahamas
- North Atlantic
-Sometimes form eddies –
circulating water that
pinches off from the
current

42. More Currents
1. Upwelling & Downwelling currents:

43. 2. RIP CURRENTS
• Narrow, powerful surface currents which flow away from the shore.
• Caused by pressure from uneven buildup of water from waves.
• Can flow very quickly and can be difficult to detect until you are in one.
Rip currents don’t pull swimmers under, they flow out and can carry
swimmers for several miles.

45. 3. Longshore Current – localized surface current
 Flows parallel to shore; move sediment along the beach

46. Longshore Currents

47. Deep Currents
 Cold, dense, salty; move by density forces and
gravity; move slower than layers above
Example: The Global Conveyer Belt = deep current that is the
lower 20% of the ocean; takes about 1,000 years to complete
the cycle

48. Global Conveyer Belt
Thermohaline circulation links the Earth's oceans. Cold, dense,
salty water from the North Atlantic sinks into the deep and drives
the circulation like a giant plunger.
http://www.columbia.edu/cu/record/23/11/13.html
Graphic - http://www.grida.no/climate/vital/32.htm

49. Other Currents
 Gyres – large circular currents in the
ocean basin
 Example: North Atlantic Gyre = consists of
4 separate currents – N. Equatorial, Gulf
Stream, N. Atlantic Drift and Canary
Currents

51. Ocean Currents & Living Things
 Currents are important to marine life as
they help move carbon dioxide, oxygen,
food, and other nutrients, making them
available for photosynthesis and
consumption.
 They have a major impact on fishing –
circulating organic nutrients that support
productive fisheries

53. Other Uses of Ocean Currents
Migration
Navigation
Weather

54. Research:
1. The Great Pacific Garbage
Patch
2. El Nino/La Nina
3. Currents and Fisheries
4. The Gulf Stream and its
effect on the Bahamas
5. The Bermuda Triangle

55. More Currents
1.Upwelling current: cold, nutrient rich;
result of wind
2.Western Boundary currents: warm &
fast, e.g. Gulf Stream
3.Eastern Boundary currents: broad, slow,
cool & shallow, associated with upwelling

56. Quiz Time!!!!
http://oceanworld.tamu.edu/students/curre
nts/currents_quiz.htm