Download OCEAN CURRENTS

11.2 Ocean Currents
• There are more than 20 major currents which move
large amounts of water predictably around the
oceans.
 Currents move large quantities of water, minerals,
solar energy, oxygen and carbon dioxide, plankton
and fish.
 Currents are caused and driven by water density
and salt content, the wind, the spin of Earth,
coastlines and the moon.
 Largest current is the Antarctic Circumpolar
Current in the Southern Ocean, at 24 000 km long
See page 414 - 416
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Ocean Currents
• Ocean currents are either
 Surface currents (0 - 200 m)
 Deep water currents (200 m and deeper)
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What Makes Surface Currents Move?
• Wind
 As air warms from solar energy, it rises, and cooler air rushes
to replace it. This creates wind.
 As the wind passes along the surface of the water, it bumps the
water molecules and moves them along in the same direction.
• Spin of the Earth
 Earth spins from West to East (counter clockwise)
 The Coriolis effect deflects winds and currents to
the right/East in the Northern hemisphere
(opposite in the Southern hemisphere)
• Shape of continents
 Currents move through the oceans and around
See page 416 - 417
the continents like rocks in a stream.
(c) McGraw Hill Ryerson 2007
What Makes Deep Currents Move?
• Water temperature
 Like air, warm water rises, and cool water falls
 Density current = cool, dense water moving on an ocean floor.
 Three layers of water dependent on temperature:
 Surface: 0 - 200 m, warmest
 Thermocline: 200 m - 1 km, rapidly cools
 Deep water: 1 km and deeper, just above freezing
See page 418 - 420
(c) McGraw Hill Ryerson 2007
What Makes Deep Currents Move?
• Water salinity
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Adding fresh water decreases salinity
Evaporation and freezing increases salinity
Densest ocean waters at the poles
Upwelling occurs when nutrient-rich
cold water finally moves up to the surface
(c) McGraw Hill Ryerson 2007
Ocean Waves and
Their Effect on Shaping Land
• Most waves are created by wind.
• In open ocean, waves are called swells.
 Swells “break” in shallow water, show characteristic curl.
• The largest waves are tsunamis, caused by undersea
earthquakes, landslides or volcanic eruptions.
See page 421
(c) McGraw Hill Ryerson 2007
Ocean Waves and Their Effect on
Shaping Land
• Waves erode coastal areas based on the force of the
waves, and the composition of the shoreline.
 Headlands made up of harder rock, and erode less, but
absorb most wave force.
 Bays occur between headlands, are generally calm.
 Sea stacks are extra-hard rock left behind
from eroded headlands.
(c) McGraw Hill Ryerson 2007
Tides
• Tides are caused by gravities of Earth and the Moon.
 High tides occur where the Moon is
closest to Earth (and opposite side)
 Low tides occur at 90º to the high tides.
(c) McGraw Hill Ryerson 2007
Tides
• Tidal range (difference between high and low)
averages 3 m in BC.
• The Sun’s gravity, when lined up properly, can
produce extreme tides.
 These are called spring tides
 When the Sun, Moon and Earth are not lined up,
the tides are called neap tides.
See page 423 - 424
Take the Section 11.2 Quiz
(c) McGraw Hill Ryerson 2007