1 Earth's Oceans

82409_7chapter_13_earths_oceans.pdf Copyright © by Holt, Rinehart and Winston. All rights reserved.

Interactive Textbook 229 Exploring the Oceans

SECTION

1Earth"s Oceans

Exploring the Oceans

Name Class DateCHAPTER 13

After you read this section, you should be able to answer these questions:

• What affects the salinity of ocean water?

• What affects the temperature of ocean water? • How does the ocean affect air temperatures?

What Is the Global Ocean?

Earth has more liquid water on its surface than any other planet in the solar system. In fact, 71% of Earth"s surface is covered by liquid water. Most of Earth"s water is found in its oceans. There are five main oceans on Earth. However, the oceans are all connected to each other. Therefore, scientists often refer to all the oceans on Earth as the global ocean. The continents divide the global ocean into the five main oceans. The largest ocean is the Pacific Ocean. The Atlantic Ocean is the second largest ocean. It has half the volume of the Pacific Ocean. The Indian Ocean is the third largest ocean. The Southern Ocean extends from the coast of Antarctica to 60°S latitude. The Arctic Ocean is the smallest ocean. Much of its surface is covered by ice. The figure below shows where these oceans are found. Atlantic Ocean

Pacific Ocean

Indian OceanArctic Ocean

Southern Ocean

BEFORE YOU READ

National Science Education Standards

ES 1b, 1f, 1g, 1h, 1j, 2aSTUDY TIP

Ask Questions As you read

this section, write down any questions you have. After you read, discuss your questions in a small group.

READING CHECK1.DescribeWhat divides

the global ocean into fi ve parts?

TAKE A LOOK

2.IdentifyWhat are the fi ve

main oceans? Copyright © by Holt, Rinehart and Winston. All rights reserved.

Interactive Textbook 230 Exploring the Oceans

SECTION 1

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Earth"s Oceans continued

How Did The Oceans Form?

Soon after the Earth formed, it was very different than it is today. There were no oceans. Volcanoes produced large amounts of ash, dust, and gases, including water vapor. These gases began to form the atmosphere. Slowly, Earth cooled. By about 4 billion years ago, the temperature was low enough for the water vapor in the atmosphere to condense. The liquid water fell as rain. The rain filled the basins in Earth"s surface, and the first oceans formed. Plate tectonics has caused the shapes and locations of Earth"s oceans to change over time.

About 245 million years

ago, the continents were joined into one large land mass. The oceans were one large body of water.

By about 180 million

years ago, the con- tinents had started to break apart. The

North Atlantic Ocean

and the Indian Ocean began to form.

By about 65 million

years ago, most of the

Atlantic Ocean had

formed. However, the

South Atlantic Ocean

was much narrower than it is today.

Today, the continents

are still moving slowly, about 1 to

10 cm per year. The

Pacifi c Ocean is get-

ting smaller. Howev- er, many of the other oceans are growing.

READING CHECK

3.IdentifyWhere did some

of the gases that formed

Earth"s atmosphere come

from?

STANDARDS CHECK

ES 1b Lithospheric plates on the

scales of continents and oceans constantly move at rates of centimeters per year in response to movements in the mantle.

Major geological events, such as

earthquakes, volcanic eruptions, and mountain building result from these plate motions.

Word Help: response

an action brought on by another action; a reaction

Word Help: major

of great importance or large scale

4.ExplainWhy have the

shapes and locations of the oceans changed with time? Copyright © by Holt, Rinehart and Winston. All rights reserved.

Interactive Textbook 231 Exploring the Oceans

SECTION 1

Name Class Date

Earth"s Oceans continued

Why Is Ocean Water Salty?

Ocean water is different from the water that we drink. People cannot use ocean water for drinking because it is salty. Most of the salt in the ocean is the same kind of salt we use on our food. This type of salt is called sodium chloride. It is a compound made from the elements sodium, Na, and chlorine, Cl. Ocean water also contains other dissolved solids, including magnesium and calcium. These dissolved solids make the water taste salty.

This graph shows the

amounts of different kinds of solids in ocean water. As rivers and streams flow toward the ocean, they dissolve minerals from rocks and soil. These minerals include halite (sodium chloride) and calcite (calcium carbonate). The rivers carry the dissolved minerals to the ocean. At the same time, liquid water in the oceans evaporates to form water vapor. As the water evaporates, it leaves behind the minerals that were dissolved in it.

What Is Salinity?

Salinity is a measure of the amount of solid material that is dissolved in a certain amount of liquid. It is usu- ally measured as grams of dissolved solids per kilogram. On average, ocean water has 35 g/kg of dissolved solids in it. This means that 1 kg of ocean water has about of solids dissolved in it. If you evaporated 1 kg of ocean water, of solids would remain.

Math Focus

5.Read a Graph Which two

elements make up most of the dissolved solids in sea water?

READING CHECK

6.IdentifyWhere does

most of the salt in the ocean come from? Copyright © by Holt, Rinehart and Winston. All rights reserved.

Interactive Textbook 232 Exploring the Oceans

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Earth"s Oceans continued

EFFECTS OF LOCATION ON SALINITY

Some parts of the ocean are saltier than others. Most oceans in hot, dry climates have high salinities. In these areas, the hot weather causes water to evaporate quickly. Salt is left behind. For example, the Red Sea in the Middle East is very salty. The climate there is very hot and dry. Some parts of the ocean are less salty than others. Along the coastlines, fresh water from streams and rivers runs into the ocean. As fresh water mixes with ocean water, the salinity of the ocean water decreases. For example, the salinity of the ocean waters near the Amazon River is much lower than the salinity in other parts of the ocean. KILOGRAMOFSEAWATER

This fi gure shows the salinity of ocean

water in different parts of the world.

EFFECTS OF WATER MOVEMENT ON SALINITY

The movement of water also affects salinity. Slow- moving ocean water tends to have higher salinity than fast-moving water. Parts of the ocean with slow-moving water, such as gulfs, bays, and seas, often have high salin- ities. Parts of the ocean without currents are likely have higher salinities as well.

What Affects Ocean Temperatures?

The temperature of ocean water decreases as depth increases. However, the temperature change is not uni- form. Scientists can divide the water in the ocean into three layers based on how temperature changes. These three layers are the surface zone, the thermocline, and the deep zone.

READING CHECK

7. ExplainWhy do oceans

in hot, dry climates tend to have high salinity?

TAKE A LOOK

8.InferThe Gulf of Mexico

is located between Mexico and Florida. Why is the ocean water in the Gulf of Mexico less salty than in other places?

READING CHECK

9.DescribeHow does water

movement affect salinity? Copyright © by Holt, Rinehart and Winston. All rights reserved.

Interactive Textbook 233 Exploring the Oceans

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Earth"s Oceans continued

Water depth (m)

Water temperature (°C)1,200

0 5 10

1,0008006004002000

15 202530

Surface zone The surface zone is the warm,

top layer of ocean water. It extends to about

300 m below the surface. Sunlight heats the

top 100 m of the surface zone. Convection currents mix the heated water with the cooler water below.

ThermoclineThe thermocline is the layer of

water below the surface zone. It extends to between 700 m and 1,000 m below the sur- face. In the thermocline, temperature decreases quickly as depth increases.

Deep zoneThe deep zone is the deepest

layer of the ocean. The temperature in the deep zone is only about 2°C.

SURFACE ZONE

Thesurface zone is the top layer of ocean water. It is heated by energy from the sun. As the ocean water is heated, it becomes less dense and rises above denser, cooler water. Convection currents form as the water moves. These currents can move heat within the surface zone to a depth of 100 m to 300 m. Therefore, the water temperature within the surface zone is fairly uniform.

THERMOCLINE

Thethermocline is the layer of the ocean just beneath the surface zone. Within the thermocline, the temperature of the water decreases a lot as depth increases. This is because the sun cannot heat the water below the surface zone. In addition, the warm water of the surface zone cannot mix easily with the water below. The depth of the thermocline is different in different places. It can extend from 100 m to almost 1,000 m below the surface of the ocean.

DEEP ZONE

Thedeep zone is the layer below the thermocline.

In the deep zone, the temperature of the water is about 2°C. This very cold water is very dense. It moves slowly across the ocean floor and forms the deep ocean currents.

TAKE A LOOK

10. IdentifyHow does

warm water mix with cool water in the surface zone?

Critical Thinking

11. Predict Consequences

What would happen to the

water temperature in the surface zone if convection currents did not form there?

Explain your answer.

Ocean Temperature and Depth

Copyright © by Holt, Rinehart and Winston. All rights reserved.

Interactive Textbook 234 Exploring the Oceans

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Earth"s Oceans continued

CHANGES IN SURFACE TEMPERATURE

The temperature of water at the surface of the ocean is different in different places. Surface water along the equator is warmer than at the poles. This is because more sunlight reaches the equator than the poles. Surface water at the equator can be up to 30°C. In the polar oceans, water at the surface can be as cold as ?1.9°C. The temperature of water at the surface of the ocean can also change during different times of year. Many areas receive more sunlight in the summer than in the winter. In these areas, the surface water in the oceans is warmer in the summer.

How Does Water Move on Earth?

Imagine that you could see Earth from outer space. You would see green and brown landmasses, blue oceans, and white clouds. These parts are involved in the water cycle, which is shown below. The water cycle is the movement of water between the atmosphere, the ocean, and the land. The ocean is important to the water cycle because it holds nearly all of the Earth"s water.

READING CHECK

12. ExplainWhy is surface

water warmer at the equator than at the poles?

READING CHECK

13. Defi ne What is the

water cycle?

TAKE A LOOK

14. IdentifyWhere does

most precipitation fall? Copyright © by Holt, Rinehart and Winston. All rights reserved.

Interactive Textbook 235 Exploring the Oceans

SECTION 1

Name Class Date

Earth"s Oceans continued

How Do the Oceans Affect Air Temperatures?

You may know that many living things depend on

the oceans for food and shelter. However, the oceans also help to keep the rest of the planet suitable for liv- ing things. This is because the oceans absorb and hold energy from sunlight. This helps to keep temperatures in the atmosphere from changing too much.

The ocean absorbs and releases heat much more

slowly than the land does. Air can absorb heat from the oceans. Therefore, the oceans help to keep air tempera- tures steady, as shown below.

Sunlight heats ocean water, air,

and land during the day.

The air and the land

lose their heat quickly.The ocean loses heat slowly. The air absorbs heat from the ocean during the night.

The air temperature

stays steady. If there were no oceans on Earth, the air temperature could vary from above 100°C to below ?100°C in a single day! Such large temperature changes could cause a lot of severe weather. Life as we know it could not exist in these conditions. The ocean can also affect the climate of different areas. Remember that ocean water at the equator is warmer than ocean water at the poles. Currents in the ocean move the ocean water from place to place. This helps to distribute heat throughout the Earth. The warm water from the equator can flow past land at high latitudes. The air absorbs heat from the warm ocean water. As a result, the land can have milder tem- peratures than other areas at the same latitude. For example, the islands of the United Kingdom are at about the same latitude as parts of Canada. However, a warm ocean current flows past the United Kingdom. As a result, its climate is much warmer than much of Canada"s.

STANDARDS CHECK

ES 1j Global patterns of atmo-

spheric movement infl uence local weather. Oceans have a major effect on climate, because water in the oceans holds a large amount of heat.

Word Help: major

of great importance or large scale

15. ExplainHow do

the oceans affect air temperatures?

READING CHECK

16. IdentifyWhat helps to

distribute the heat in ocean water? Copyright © by Holt, Rinehart and Winston. All rights reserved.

Interactive Textbook 236 Exploring the Oceans

Name Class Date

Section 1 Review NSESES 1b, 1f, 1g, 1h, 1j, 2a

SECTION VOCABULARY

salinitya measure of the amount of dissolved salts in a given amount of liquidwater cycle the continuous movement of water between the atmosphere, the land, and the oceans 1. Explain Why do scientists call the ocean water on Earth the global ocean? 2. Identify What are two factors that can affect salinity? 3. Identify Relationships Why do most oceans in hot, dry climates have high salinities? 4. Explain Why does the temperature in the thermocline decrease quickly with depth? 5. Explain In the space below, make a drawing of the water cycle. Explain what is happening in each part of your drawing. Copyright © by Holt, Rinehart and Winston. All rights reserved.

Interactive Textbook Answer Key 50 Earth Science

Earth Science Answer Key continued 6. A glacier deposits unsorted material if, as it melts, the sediment in it drops to the ground. A glacier deposits sorted material if, as it melts, its water carries smaller sedi- ment farther than larger sediment.

SECTION 4 THE EFFECT OF GRAVITY ON

EROSION AND DEPOSITION

1. the steepest slope at which particles do not move downhill 2. The slope is greater than the angle of repose. 3. They can carry away, bury, and destroy habitats. 4. heavy, wet soil; removal of plant roots; earthquakes; construction 5. Water probably decreases the angle of repose, because wetting soil that is not mov- ing can cause it to start moving downhill. 6. Creep happens slowly. 7.

Type of mass

movementDescription

Landslide Material moves suddenly and rapidly

down a slope.

Rock fall Loose rocks fall down a steep slope.

Mudfl ow A large amount of mud moves

downhill very quickly.

Lahar Water mixes with volcanic ash to

produce a fast-moving, dangerous mudfl ow.

Creep Material moves downhill very slowly.

Review

1. landslides, mudflows, rock falls, creep, lahars 2. Mass movement can cause property damage and injury. 3. If the angle of a slope is greater than the angle of repose, mass movement will occur. 4. gravity 5. Landslides involve the fast movement of large amounts of materials of many different sizes. In mudflows, there is fast movement of mud only. 6. size, shape, weight, and composition of the particles making up the material

Chapter 13 Exploring the

Oceans

SECTION 1 EARTH"S OCEANS

1. the continents 2. Pacific, Atlantic, Indian, Southern, Arctic 3. volcanoes 4. Plate tectonics has caused the continents to move. 5. sodium and chlorine 6. rocks and minerals on land 7. The hot, dry weather causes ocean water to evaporate, and salt is left behind. 8. The Mississippi River brings fresh water into the Gulf of Mexico. 9. Fast-moving water tends to have low salinity.

10. by convection11. The temperature would be less uniform,

because the cool and warm water would not mix as efficiently.

12. The equator receives more sunlight.

13. the movement of water between the ocean,

the atmosphere, and the land

14. into the oceans

15. Air absorbs heat from the oceans.

16. currents

Review

1. All of the oceans are connected, so water and other materials can flow between them.

Therefore, they can all be considered to be

part of a single body of water. 2. water movement and climate 3. The hot, dry climate causes water to evapo- rate from the oceans, but the salt remains behind in the liquid water. 4. The sun cannot heat the water in the thermo- cline, and the warm water above cannot easily mix with the colder water. 5. A simple diagram of the water cycle should be drawn. It should include descriptions of evaporation, condensation, and precipitation.

SECTION 2 THE OCEAN FLOOR

1. The pressure there is too high for people to survive without a ship. 2. They need to be thick in order to withstand the high pressures in the deep ocean. 3. a process in which sound signals are used to determine the distance to an object 4. The time for sound to travel to the ocean floor is 2 s. Then, 2 s × 1,500 m/s ? 3,000 m. 5. continental margin, deep-ocean basin 6. continental shelf, continental slope, continental rise 7. continental shelf, continental slope, continental rise