(c) McGraw Hill Ryerson 2007

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

Ocean Currents

• Ocean currents are either Surface currents (0 - 200 m) Deep water currents (200 m and deeper)

(c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007

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

the continents like rocks in a stream. See page 416 - 417

(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

What Makes Deep Currents Move?

• Water salinity 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

(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

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

(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