1. Ocean Currents
Earth Science

2. Ocean Currents Currents- water in a stream
Surface currents- currents that move on or near the surface & are caused by wind
Deep current- move very slowly beneath the surface of the ocean & are caused by density differences in water

3. Ocean Currents: Surface Currents
Driving energy source for surface currents is wind
Surface currents extend down to a depth of 100m
3 controlling factors in surface currents
Wind belts
Earth’s rotational effects
Location of the continents

4. Ocean Currents: Surface Currents
Wind belts
Most directly affect the surface currents
Trade winds & westerlies
Trade winds at latitudes north & south of the equator
Westerlies are located in the middle latitudes
North of the equator the trade winds blow from the northeast (Northern Hemisphere) & are usually warm
Southern Hemisphere trade winds blow from the south east
In both hemispheres they push water to the west

5. Wind Belts
Northern Hemisphere westerlies blow from the southwest…moves currents eastward across the Atlantic & Pacific Oceans
Southern Hemisphere westerlies blow from the northwest…moves currents eastward
Produce the largest current on earth…West Wind Drift
Travels the entire circumference of the earth and is located in the southern part of all 3 major oceans

6. Ocean Currents: Surface Currents
Coriolis Effect
Deflection of the earth’s winds and ocean currents based on the rotation of earth
Coriolis effect along with the earth’s winds cause gyres
Gyres- huge circle of moving water
Northern hemisphere- gyre moves clockwise
Southern hemisphere- gyre moves counterclockwise

7. Ocean Currents: Surface Currents
Continents
The surface current flows against a landmass and is divided and deflected
Equatorial Current
Warm currents
2 of them both move in a westward direction

8. Ocean Currents: Surface Currents
North Pacific & Atlantic Currents
North Atlantic
North Atlantic Equatorial Current
Warm current that moves water north along the east coast of North America called the Gulf Stream
Gulf Stream widens & slows and becomes the North Atlantic Drift
Drift- weak current
All of those currents form the North Atlantic Gyre

9. Ocean Current: Surface Currents
North Pacific
Similar to the North Atlantic
Japan Current is equivalent to the Gulf Stream
Flows northward & turns into the North Pacific Drift when it spreads out & slows down as it flows towards North America

10. Ocean Currents: Surface Currents
Currents in the Southern Hemisphere
Currents here also flow in gyres but in a counterclockwise direction
Southern regions of all three major oceans constant westward winds produce the West Wind Drift
West Wind Drift is the largest current in the world
Because there is no continents to stop it the West wind drift completely circles Antarctica

11. Ocean Currents: Surface Currents
Currents in the Southern Hemisphere cont…
Indian Ocean currents follow 2 patterns
Southern part the currents follow a counterclockwise gyre
Northern part the currents are governed by monsoons
Monsoons change directions with the seasons

12. Ocean Currents: Deep Currents
Cold, dense currents that flow beneath the surface of the ocean
Much slower moving than surface currents
Produced as cold, dense water of the polar regions sinks & flows beneath warmer ocean water toward the equator
Movements are the result of density differences
Higher density of polar waters is also a result of an increase in salinity
Deep-current layer rises only when winds blow the surface water out of the way

13. Ocean Currents: Deep Currents
Antarctic Bottom Water
The densest & coldest ocean water in the world
Dense, cold water sinks to the bottom & very slowly move north forming the Antarctic Bottom Water current
Moves to north to about 40 degrees & takes several hundred years to make the trip

14. Ocean Currents: Deep Currents
North Atlantic Deep Water
South of Greenland the water is exceptionally cold & has high salinity causing it to sink
Forms a current that travels south underneath the Gulf Stream
Flows southward all the way to the Antarctic & over the Antarctic Bottom Water
Deep Atlantic currents also are found near the Mediterranean Sea

15. Ocean Currents: Deep Currents
Turbidity Currents
Occur when large masses of sediment that have accumulated along a continental shelf or continental slope suddenly break loose and slide downward
Causes the water to become more dense than the surrounding water
Believed to cause submarine canyons to deepen

16. Ocean Waves Wave- periodic up and down movement of water
Transfer energy
2 basic parts of a wave:
Crest- highest point of a wave
Trough- lowest point of a wave
Wave characteristics
Wave height- vertical distance between a crest & a trough of a wave
Wavelength- horizontal distance between 2 crests of a wave
Wave period- time it takes for one complete wavelength
Wave speed= wavelength/period

17. Ocean Waves Wave Energy Main source of energy for waves is wind
The more energy that is transferred the larger the wave becomes
Because of surface area…
Large waves tend to become larger because the wind has more area to push on
Smaller waves tend to die out because there is a very small surface area for the wind to push on
Swell- group of long, rolling waves that are the same size

18. Ocean Waves Water Movement in A Wave
Only the energy of wave moves forward, the water itself moves very little
The water particles within the wave move in a circular motion
Circle traced by each water particle in a wave has a diameter equal to the height of the wave
Energy received by a wave decreases as depth increases because the waves receive their energy from the wind
Diameter of the circle traced by each water particle decreases as depth increases

19. Ocean Waves Wave Size 3 factors that affect wave size:
Speed of the wind
Length of time the wind blows
Fetch of a wave
Distance that the wind can blow across open water
Long fetch produces very large waves
Likely to occur during storms
Size of a wave will only increase to a certain height to length ratio before it collapses
Whitecaps- occur when high wind speeds blow the crest off of a wave

20. Ocean Waves: Waves & the Shore
Breakers
Height of a wave changes as the wave approaches the shore
As a wave moves into shallow water, the bottom of the wave is slowed by friction but the top of the wave continues to move at its original speed
The top of wave gets farther & farther ahead of the bottom & eventually it topples over & forms a breaker.
Height of the wave when it topples over is one to two time the height of the original wave

21. Ocean Waves: Waves & the Shore
Breakers cont…
Size & force of breakers are determined:
Original wave height
Wavelength
Steepness of the ocean floor close to shore
More steep = rapid increase of wave height = breaker with greater force
Pacific Coast
Less steep = slower increase of wave height = breaker with less force
Atlantic Coast

22. Ocean Waves: Waves & the Shore
Undertows & Rip Currents
Undertow- water carried onto a beach is pulled back into deeper water by an irregular current
Create problems only along shores with steep drop-offs
Rip current- form when water from large breakers returns to the ocean through channels in underwater sand bars that are parallel to the beach
Flow perpendicular to shore

23. Ocean Waves: Waves & the Shore
Longshore Currents
Form sandbars
Forms as waves approach the beach at an angle
Flow parallel to the shore

24. Ocean Waves: Wave & the Shore
Tsunamis
Most destructive waves in the ocean
Energy that forms them comes from seismic sea waves not the wind
Usually caused by earthquakes on the ocean floor, but also by volcanic eruptions & underwater landslides
Have very long wavelength, wave period is about 15 minutes, and speed of 725 km/hr
Entire depth of the water is involved in wave motion
Height increase greatly as they approach shore

25. Tides Tides- daily changes in the level of the ocean surface
The gravitational pull of the moon on the earth and its waters is the major cause of tides
Low tides are formed halfway between two high tides

26. Tides: Behavior
Tidal movement is due to the rotation of the earth and the pull of the moon.
Earth rotates from west to east, so tidal bulges appear to move westward around the earth.
Because there are two tidal bulges most locations on the ocean have two high tides & two low tides
Tidal range- difference in the level of high tide and low tide at specific locations
Can vary widely from place to place

27. Tides: Behavior
During period of new moon & full moon the high tides are the highest and the low tides the lowest
This is because the sun, moon, & earth are all aligned
These are called spring tides
During 1st quarter & 3rd quarter phases the daily tidal range is the smallest
This is because the moon & the sun are at right angles to each other in relation to the earth
These tides are called neap tides

28. Tides: Variations
Tidal patterns are greatly influenced by the size, shape, depth, & location.
Atlantic Coast: tides are semidiurnal, which means twice a day
Have a fairly regular tidal range
Gulf of Mexico: diurnal, which means once a daily
Pacific Coast: follow a mixed pattern & have an irregular tidal range
Very high followed by very low, then a lower high tide followed by a higher low tide

29. Tides: Variations
Tidal oscillations- caused by the slow rocking motions of ocean water that occur as the tidal bulges move around the ocean basins
Produce the world’s greatest tidal range in the Bay of Fundy (tidal ranges is larger than 15m)

30. Tides: Tidal Currents
Tidal current- occurs as the ocean water rises and falls with the tides, it flows toward & away from the coast.
Flood tide- when tidal current flows toward the coast
Ebb tide- when tidal current flows away from the coast
Slack water- time between flood tide and ebb tide with no tidal currents.
Tidal bore- surge of water that rushes upstream where a river meets an ocean

31. Tide Videos