Movements of the Ocean

Chapter 21

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.

Ocean Waves

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

How do Breakers Form?

Approaching the Coastline

• 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

Formation of Tides

Types of Tides

• Tidal range = difference in levels of ocean water at high tide & low tide

• Spring tides = Occurs during the new moon & full moon; results in higher high tides and lower low tides.

• Neap tides = occurs during 1st & 3rd quarter moons; daily tidal range is small.