Childrens Illustrated Encyclopedia

387

Ocean currents

the water in the oceans is constantly moving in great circular streams, or

currents, which can flow about as fast as you walk. Winds blow the surface layer

of the oceans to form these currents, which carry warm or cold water along the

shores of continents, greatly affecting the weather there. sometimes, currents

flow deep below the surface, moving in the opposite direction to surface

currents. For example, surface currents

carry warm water away from the equator,

while currents deep beneath the sea

bring cold water back to the equator.

Most seas have strong currents. But

the waters of the sargasso sea,

which lies in the north atlantic

Ocean, are almost still, causing the

sea to become choked with seaweed.

GulF streaM

Water heated by the sun flows out from the

Gulf of Mexico. this warm current crosses

the atlantic Ocean and flows around the

shores of western europe. there, the winter

weather is mild, while places on the other side of

the ocean away from the current are freezing cold.

Ocean hunters

Fishing boats sail the oceans and seas to

bring us the fish and other sea creatures

that we eat. the best fishing grounds are

in shallow seas, where the water teems

with fish. But catches must be controlled;

otherwise the numbers of fish will fall as

the fish fail to breed.

the Kon TiKi expeditiOn

early peoples may have used the

currents to travel across oceans. in 1947,

the Kon Tiki expedition, led by norwegian

explorer thor heyerdahl, tested this

theory by sailing a light wooden raft

from peru to the polynesian islands.

yOur Feet May Be restinG firmly on the ground, but more than

two-thirds of our planet is covered with water. Oceans and seas make

up 71 percent of earth’s surface. they influence the climate, supply us

with food, power, and valuable minerals, and provide a home for a

fascinating range of plant and animal life.

the oceans and seas began millions of years ago, when earth cooled

from its original molten state. Water vapor escaped from inside earth

in volcanic eruptions, cooled, and fell as rain. it filled vast hollows and

basins surrounding rocky land masses. these

gradually moved around to form the

continents and oceans as they exist

today. as rivers formed on the land

and flowed into the seas, they

dissolved minerals from the rocks,

387- Oceans and seas

Southern

Ocean

Indian Ocean

The Arctic Ocean is

an ice-covered ocean

at the North Pole.

the WOrld’s Oceans and seas

Oceans are vast bodies of water, usually

separating the continents. the pacific

Ocean, which is the largest and

deepest, lies between america

and asia and covers more than

a third of the globe. the

others, in order of size, are

the atlantic, indian, and

southern oceans. the

arctic Ocean lies between

the land masses around

the north pole and is

largely covered by ice.

seas, bays, and gulfs are

smaller bodies of water

that lie between arms of

land, or between islands and

land masses. some, such as the

caspian and dead seas, are

entirely surrounded by land and

are really not seas but large lakes.

tides

twice a day the

level of the seas rises

and falls. these changes in

level are called tides. they are

caused mainly by the pull of

the moon’s gravity on earth.

When the moon lies directly

over the ocean, its gravity pulls

the water toward it. Water also

rises on the opposite side of

earth, because earth itself is

pulled toward the moon.

sprinG tides

high, spring tides

occur when earth,

the sun, and the

moon are in line.

Indian

Ocean

Pacific

Ocean

North

Pacific

Ocean

Oceans and seas

Sun

The Southern Ocean

surrounds Antarctica. It

includes all the waters

between 60 degrees

south latitude and the

continent of Antarctica.

Moon

Rise in

water level

The Gulf Stream broadens

out, slows down, and

becomes the North

Atlantic Drift. A slow

current is called a drift.

NORTH

AMERICA

Gulf of

Mexico

Atlantic

Ocean

Gulf

Stream

Earth

EUROPE

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