Chapter 21 Section 1

Ocean CurrentsObjectives

Describe how wind patterns, the rotation of the Earth, and continental barriers affect surface currents in the ocean

Identify the major factor that determines the direction in which a surface current circulates

Explain how differences in the density of ocean waters affect the flow of deep currents

Ocean CurrentsThe water in the ocean

moves in giant streams called currents

Oceanographers study currents by examining the physical and chemical characteristics of ocean water

They also identify currents by mapping the paths of debris that is dumped or washed overboard from ships

Scientists place currents into two main categories, surface and deep currents

Ocean CurrentsCurrents that move on

or near the surface of the ocean, and are driven by winds are called surface currents

These are controlled by three factors, winds, Earth’s rotation, and location of the continents

Winds are caused by uneven heating of the atmosphere

Ocean CurrentsGlobal wind belts, such as

trade winds and the westerlies are major factors affecting the flow of ocean surface waters

Trade winds are located just north and south of the equator

In the Northern Hemisphere they blow from the north east

In the Southern Hemisphere they blow from the south east

Ocean CurrentsContinents are

another major influence on surface currents

They act as barriers to surface currents

When surface currents flow against the continents the current is deflected and divided

Ocean CurrentsGlobal wind belts

and ocean currents do not flow in straight lines, the follow a curve or circular pattern that is caused by Earth’s rotation

The Coriolis Effect cause huge circles of moving water called gyres, to form

Ocean CurrentsWarm equatorial

currents move in a western direction in the oceans

Between these westward flowing currents lies a weaker, eastward flowing current called the Equatorial Countercurrent

Ocean CurrentsIn the Southern Hemisphere

the currents in gyres move counterclockwise

In the most southerly region of the oceans constant westward winds produce the world’s largest current, the Antarctic Circumpolar Current also known as West Wind Drift

No continents interrupt the movement of the current that completely circles Antarctica

Ocean CurrentsThe Indian Ocean

surface currents follow two patterns, in the south they follow a circular counter clockwise gyre

In the north they are governed by monsoons and change seasonally

Ocean CurrentsIn the North Atlantic

warm ocean water moves through the Caribbean Sea and the Gulf of Mexico and north along the east coast of North America in a swift long current called the Gulf Stream

Further north the Labrador Current flows south and joins the Gulf Stream

Ocean CurrentsAt the poles water

cools and freezes making the water saltier and denser

The denser water sinks and begins to flow toward the equator

The journey of this cold dense water takes hundreds of years to complete

Ocean CurrentsThe temperature of

water near Antarctica is very cold and the water salinity is high

This makes the water of Antarctica the densest and coldest water in the ocean

This forms a deep current called Antarctic Bottom Water

Ocean CurrentsA strong current caused by

an underwater landslide is a turbidity current

This occurs along the continental shelf or the continental slope, and a large amount of sediment breaks loose

The cloudy water gets denser than the surrounding water, moves beneath the clear, less dense water