Unit 4

Unit 4 Unit 4

The importance of oceansThe importance of oceans

Unit 4 The importance of oceans

Where are the major oceans and seas?Where are the major oceans and seas?

361 million km² of the earth’s surface is covered by water.


Where are the major oceans and seas?Where are the major oceans and seas?Unit 4 The importance of oceans

Oceans and seas occupy 71% of the earth’s surface.

Oceans and seas occupy 71% of the earth’s surface.Oceans are unevenly distributed over the earth’s surface. Most of the southern hemisphere is covered by oceans.

Oceans are unevenly distributed over the earth’s surface. Most of the southern hemisphere is covered by oceans.The four oceans are the Pacific, the Atlantic, the Indian and the Arctic.

The four oceans are the Pacific, the Atlantic, the Indian and the Arctic.

Where are the major oceans and seas?Where are the major oceans and seas?Unit 4 The importance of oceans

km

Pacific Ocean

Atlantic Ocean

Indian Ocean

Arctic Ocean

Baltic Sea

North Sea

Mediterranean Sea

Black Sea

Caspian Sea

Red Sea Arabian Sea

The Gulf

Bay of Bengal

South China Sea

East China Sea

Yellow Sea

Sea of Japan

Sea of Okhotsk Hudson Bay

Gulf of Mexico

Caribbean Sea

°N

°N

°S

N

°

Pacific OceanPacific OceanPacific Ocean is the largest and deepest of the world’s

four oceans, covering more than a third of the earth’s surface.

The size of the Pacific Ocean is 165 000 000km², which is bounded on the east by the North and South American continents; on the north by Bering Strait; on the west by Asia; and on the south by Antarctica.

The average depth of the ocean is about 4 282 m and the greatest depth is 11 033 m in the Mariana Trench.

Much of the plant and animal life of the Pacific Ocean is concentrated along its margins.


Atlantic OceanAtlantic OceanAtlantic Ocean is the second largest of the earth’s four

oceans and the most heavily travelled.

The Atlantic Ocean has a surface area of 82 000 000

km².

The Atlantic Ocean is an “S-shaped” north-south

channel, extending from the Arctic Ocean in the north to the Antarctic continent in the south. It is situated between the western coast of the American continents and the eastern coasts of Europe and Africa.

The Atlantic Ocean has an average depth of 3 926 m.

The greatest depth is 8 742 m in the Puerto Rico Trench.


Indian OceanIndian OceanIndian Ocean is the third largest of the earth’s

four oceans, bounded on the west by Africa, on the north by Asia, on the east by Australia, and on the south by Antarctica.

The total area of the Indian Ocean is 73 400 000 km². The average depth is 4 210 m and the deepest point is 7 725 m, off the southern coast of the Indonesian island of Java.

The Indian Ocean contains numerous islands, the largest of which are Madagascar and Sri Lanka.

Tropical storms occur occasionally and the ocean is notable for seasonal winds called monsoons.


Arctic OceanArctic OceanArctic Ocean is the smallest of the four world oceans.

The Arctic Ocean extends south from the North Pole to the shores of Europe, Asia and North America.

The total surface area of the Arctic Ocean is 14 000 000 km². The average depth is 1 500 m and the deepest point in the Arctic Ocean is 5 450 m in the Pole Abyssal Plain near the North Pole.

Sea ice is formed by the freezing of seawater which is the most extensive form of ice in the Arctic Ocean.

In winter a permanent cap of sea ice covers all of the

ocean surface.


Why are oceans important?Why are oceans important?Recreation

Most of us are familiar with our beaches and seas as these are places for recreation.


We go there for swimming in the hot summer season. They are also places for surfing, sailing and fishing.

Why are oceans important?Why are oceans important?Trade and shipping

Oceans have been used for transporting raw materials and manufactured products.

Sea transport is the cheapest way of sending products in large quantity over a long distance.


Why are oceans important?Why are oceans important?Trade and shipping

Shipping routes link up industrial and densely populated regions in the world.

Oceans are important as over 70% of world trade is carried out by ships.


Major sea routes of the worldMajor sea routes of the worldUnit 4 The importance of oceans

°N

°N

°S

km

Pacific Ocean

Atlantic Ocean

Indian Ocean

Asia

Africa

EuropeNorth America

South America

Sea route

N

Arctic Ocean

Australasia

°

Why are oceans important?Why are oceans important?Unit 4 The importance of oceans

Fish for food

Oceans are rich in animal life. There are 20 000 species of fish in the oceans.

Why are oceans important?Why are oceans important?Fish for foodFish is a major sour

ce of food, today fish supplies almost 20% of the world’s animal protein.


Why are oceans important?Why are oceans important?Fish for foodFish caught are used for the

making of animal feed, fertilizer, soaps and other commercial products.

Millions of people depend upon fishing for their livelihood.


Why are oceans important?Why are oceans important?MineralsOceans are rich in minerals.Tin, gold, platinum and

diamonds are found in the sand and gravel along the shore.


Why are oceans important?Why are oceans important?MineralsSea water is an important source of salt and

fresh water.


Why are oceans important?Why are oceans important?Continental shelves are gently sloping plains beneath the sea bordering the continentals. They are no more than 100 fathoms (180m) deep.

Energy


Sea level

100 Fathoms

Continental shelf

Land

Why are oceans important?Why are oceans important?

Energy

Oceans are a potential source of renewable energy.

Modern technology has made the mining of oil in the deep sea possible.

It is possible to make use of sea waves and tidal currents for the generation of electricity.


Why are oceans important?Why are oceans important?Ocean-atmosphere system

Oceans act as a store house for the heat energy coming from the sun.

The stored heat is then radiated back to the atmosphere thus keeping the atmosphere warm.


The ocean-atmosphere systemThe ocean-atmosphere systemUnit 4 The importance of oceans

Sun

Less solar energy

Ocean

More solar energy

Warmer water

Equator

Colder water Colder water

Arctic circle Antarctic circle

0°66 1/2°N 66 1/2°S

Surface

Cold current

Warm current

Ocean absorbs sun’s energyOcean warms the atmosphere and supplies it with moistureWarmer water flows to colder sea forming warm ocean current Colder water flows to warmer sea forming cold ocean current

Atmosphere

Ocean-atmosphere system

Our oceans supply the atmosphere with moisture and heat.

The heat absorbed by the ocean is released to the atmosphere when air comes into contact with the ocean surface.

The air also absorbs from the ocean its moisture.

When this wet air blows onshore from ocean to land, it brings rain to coastal areas.

Why are oceans important?Why are oceans important?Unit 4 The importance of oceans

Why are oceans important?Why are oceans important?Ocean currents and climate

Difference in temperature leads to the different density of water over various parts of the ocean. The result is warmer water moves from tropical areas to polar areas while colder water moves from polar areas to tropical areas.

Ocean currents influence the temperature of the coastal regions they flow past. A warm current raises the temperature of the coast while a cold current lowers it.

The effect of the movement of ocean currents is important to our climate as it reduces the extremes in temperature of both the oceans and the atmosphere.


Ocean currents of the worldOcean currents of the world

Arctic Ocean

Pacific Ocean

Indian Ocean

Atlantic Ocean

Cold current Warm current

Bra

zil c

urre

nt

West Wind Drift

Peruvian Current

California C

urrent

North A

tlantic

Drif

t

Europe

Can

arie

s C

urre

nt

Asia

Benguela Current

Africa

West Australian Current

km

Australasia

North Equatorial Current

East Australian Current

South Equatorial Current

Kuro SiwoOya

Siw

o

Agu

lhas

Cur

rent

Labrador

Current

Gulf Stre

am

North America

South America

°N

°N

°S

N


Rain

Clouds

Ocean

Condensation to form clouds and rain

Wind moves up the slope and cools

Wet on-shore wind

On-shore wind from ocean brings rainOn-shore wind from ocean brings rainThe air absorbs from the ocean its moisture. When this wet air blows on-shore from ocean to land, it brings rain to coastal areas.


Hong Kong

Fog

Pacific Ocean

Cool sea surface

Warm tropical air moves northwards

South China Sea

N

Why are oceans important?Why are oceans important?Fog and typhoonsIn Hong Kong fog occurs in spring when warm

air passes over the cold sea surface.


Why are oceans important?Why are oceans important?Fog and typhoonsWe receive a lot of rain in summer as winds blow

in from the ocean.

Condensation forms fog

Warm tropical air move northwards

South China Sea

Sea surface still cool in spring


Hong Kong Pacific Ocean

Tropical sea supplies typhoons with heat and moisture

Routes of typhoons

N

Why are oceans important?Why are oceans important?Fog and typhoons Typhoons affecting us in the summer season

obtain their moisture and heat from the ocean. The heat produces an enormous amount of energy

which makes these storms very destructive.


Terms to learn

Continental shelf (Continental shelf ( 大陸架大陸架 )) -- a gently sloping plain beneath the sea bordering a continent. It is no more than 100 fathoms (180m) deep.

Renewable energy (Renewable energy ( 再生能源再生能源 )) -- energy that will never be used up. Sea waves and tidal currents are examples.


Unit 4

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