Movements of the Ocean Chapter 21. Ocean Currents Ocean currents are moving streams of water within...
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Transcript of Movements of the Ocean Chapter 21. Ocean Currents Ocean currents are moving streams of water within...
Ocean Currents
• Ocean currents are moving streams of water within the ocean.
• There are two types of currents: surface currents and deep currents.
Surface Currents
• Currents that move on or near the surface of the ocean
• 3 factors that control surface currents – air currents, Earth’s rotation, and location of continents
• All surface currents are affected by winds
Global Wind Belts
• Global wind belts are a major factor affecting the flow of ocean surface water.
• Trade winds – located just north & south of equator. Winds blow from northeast in the Northern Hemisphere and blow from southeast in Southern Hemisphere
• Westerlies are located in the middle latitudes. Blow from southwest in Northern Hemisphere and from northwest in Southern Hemisphere
Continental Barriers• Continents act as barriers to major
surface currents.• When current flows against a continent,
the current is deflected & divided.• Coriolis effect = curving path of oceans &
winds due to Earth’s rotation• Gyres = wind belts & Coriolis effect cause
huge circles of moving water.• Gyres move clockwise in Northern
Hemisphere and counterclockwise in the Southern Hemisphere.
Deep Currents
• What causes deep currents to move if the wind doesn’t have an effect on it?
• Water density moves the water. • Cold water is more dense and it sinks
and moves.• Warm water is less dense and it rises.• Note: surface currents travel much
faster than deep ocean currents.
What is a Wave?
• A wave is a periodic disturbance in a solid, liquid, or gas as energy is transmitted through the medium.
• Another kind of wave is described as the periodic up-and-down movement of water. Caused mainly by winds.
Wave Features
Wave period = the time it takes 2 consecutive wave crests to pass a given point. A wave’s speed is calculated by dividing wavelength over wave period.
Water Movement in a Wave
• Like the bottle in the diagram, water molecules do not travel horizontally through the water with the wave.
Since waves receive their energy from wind pushing against the surface of the ocean, then energy received decreases
as the depth of the water increases
Wave Size• 3 factors determine the
size of the wave– Speed of the wind– Length of time wind
blows– Fetch – distance wind
can blow across open water
• Large waves produced by strong, steady winds blowing across a long fetch.
• When wind blows crest of wave off, whitecaps are formed
Whitecaps
• Undertow – water carried onto a beach by breaking waves pulled back into deeper water by gravity. This motion forms an irregular current.
• Rip currents – forms when water from large breakers returns to the ocean through channels that cut through underwater sandbars that are parallel to the beach.
• Longshore currents – form when waves approach the beach at an angle.
Tides
• Periodic rise and fall of water level in the oceans
• High tide – water level is at its highest
• Low tide – water level is at its lowest
Cause of Tides
• The gravitational pull of the moon on Earth and Earth’s waters is the major cause
• Sun also causes tides but they are smaller because the sun is so much farther from Earth than the moon