oceanography

Objectives• Identify methods used by scientists to study

Earth’s oceans.

The Oceans

• Discuss the origin and composition of the oceans.

• Describe the distribution of oceans and major seas.

The Oceans• Oceanography is the scientific study of Earth’s

oceans.

• In the late 1800s, the British Challenger expedition became the first research ship to use relatively sophisticated measuring devices to study the oceans.

The Oceans

Modern Oceanography• In the 1920s, the German research ship Meteor

used sonar for the first time to map the seafloor features of the South Atlantic Ocean.

The Oceans

• Sonar, which stands for sound navigation and ranging, uses the return time of an echo and the known velocity of sound in water to determine water depth.

– The velocity of sound in water is 1500 m/s.

– To calculate the distance to the ocean floor, multiply the time by 1500 m/s, then divide by 2.

Modern Oceanography

Advanced Technology

The Oceans

– Satellites such as the Topex/Poseidon continually monitor the ocean’s surface temperatures, currents, and wave conditions.

– Submersibles, or underwater vessels, investigate the deepest ocean trenches.

– Large portions of the seafloor have been mapped using side-scan sonar.

– Side-scan sonar is a technique that directs sound waves to the seafloor at an angle, so that the sides of underwater hills and other topographic features can be mapped.

Origin of the Oceans• Studies of radioactive isotopes indicate that

Earth is about 4.6 billion years old.

The Oceans

• Radioactive studies and lava flows offer evidence that there has been abundant water throughout Earth’s geologic history.

Origin of the Oceans

Where did the water come from?

The Oceans

– Scientists hypothesize that Earth’s water could have originated from two sources.

• Comets occasionally collide with Earth and release water on impact–possibly enough to have filled the ocean basins over geologic time.

• Studies of meteorites indicate that they may contain up to 0.5 percent water.

• If the early Earth contained the same percentage of water, it would have been more than sufficient to form the early oceans.


Volcanism

The Oceans

– Shortly after the formation of Earth, violent volcanism released huge amounts of water vapor, carbon dioxide, and other gases, which combined to form Earth’s early atmosphere.

– As Earth’s crust cooled, the water vapor gradually condensed into oceans.


Volcanism

The Oceans

– Volcanism still adds water to the hydrosphere, but the process is balanced by the continuous destruction of some water molecules by ultraviolet radiation from the Sun.

Distribution of Earth’s Water• The oceans contain 97 percent of the water

found on Earth.

The Oceans

• The remaining 3 percent is freshwater located in the frozen ice caps of Greenland and Antarctica and in rivers, lakes, and underground sources.

• The percentage of ice has ranged from near zero to as much as 10 percent of the hydrosphere over geologic time.

Distribution of Earth’s Water• Global sea level is the level of the oceans’

surfaces.

The Oceans

– Sea level has risen and fallen by hundreds of meters in response to melting ice during warm periods and expanding glaciers during ice ages.

– Tectonic forces that lift or lower portions of the seafloor has also affected sea level.

Distribution of Earth’s Water

The Blue Planet

The Oceans

– Approximately 71 percent of Earth’s surface is covered by oceans that have an average depth of 3800 m.

– Because most landmasses are in the northern hemisphere, oceans only cover 61 percent of the surface.

– Water covers 81 percent of the southern hemisphere.


Major Oceans

The Oceans

– There are three major oceans:

• The largest ocean, the Pacific, contains roughly half of Earth’s seawater and is larger than all of Earth’s landmasses combined.

• The second-largest ocean, the Atlantic, extends from Antarctica to the arctic circle, north of which it is often referred to as the Arctic Ocean.

• The third-largest ocean, the Indian, is located mainly in the southern hemisphere.

• The water surrounding Antarctica, south of 50° south latitude, is known as the Antarctic Ocean.


Major Oceans

The Oceans


Sea Ice

The Oceans

– The Arctic and Antarctic Oceans are covered by vast expanses of sea ice, particularly during the winter.

– An ice-crystal slush develops at the surface of the water and eventually solidifies into individual round pieces called pancake ice.

– The pieces of pancake ice thicken and freeze into a continuous ice cover called pack ice.

– Pack ice is generally several meters thick and may cover an area more than 1000 km wide.


Seas

The Oceans

– Seas are smaller than oceans and are partly or mostly landlocked.

– The Mediterranean Sea is located between Africa and Europe and was the first sea to be explored and mapped by ancient peoples.

– Notable seas in the northern hemisphere include the Gulf of Mexico, the Caribbean Sea, and the Bering Sea, which is located between Alaska and Siberia.

– All seas and oceans belong to one global ocean whose waters are thoroughly mixed.

Section Assessment

1. What is side-scan sonar?

The Oceans

Side-scan sonar is a technique that directs sound waves to the seafloor at an angle, so that the sides of underwater hills and other topographic features can be mapped.

Section Assessment

2. According to one hypothesis, how did volcanism play a part in forming Earth’s early oceans?

The Oceans

During a period of massive volcanism that occurred shortly after the formation of Earth, huge quantities of water vapor, carbon dioxide, and other gases were released. These gases formed Earth’s early atmosphere. As Earth’s crust cooled, the water vapor gradually condensed into oceans.

FL: SC.H.1.4.3, SC.D.1.4.1

______ Oceans contain 97 percent of the water found on Earth.

______ Oceans cover 71 percent of Earth’s surface.

______ The Earth’s major oceans are isolated from each other by landmasses.

______ Presently, average global sea level is rising 1 to 2 cm per year.

Section Assessment

3. Identify whether the following statements are true or false.

The Oceans

true

true

false

false

Objectives• Compare and contrast the physical and chemical

properties of seawater.

• Explain ocean layering.

• Describe the formation of deep-water masses.

– salinity

– temperature profile

– thermocline

Vocabulary

Seawater

Seawater• Seawater is a solution of about 96.5 percent

water and 3.5 percent dissolved salts.

Seawater

• The most abundant salt in seawater is sodium chloride (NaCl).

• Most elements on Earth are present in seawater.

• Because these substances are dissolved, they are in the form of ions.

Seawater

Seawater

Chemical Properties of Seawater• Salinity is a measure of the amount of

dissolved salts in seawater that is expressed as grams of salt per kilogram of water, or parts per thousand (ppt).

Seawater

• The total salt content of seawater is, on average, 35 ppt, or 3.5 percent.

• Seawater also contains dissolved gases and nutrients.

Chemical Properties of Seawater

Variations in Salinity

Seawater

– The actual salinities of the oceans vary from place to place.

• Salinities may be as high as 37 ppt in subtropical regions where rates of evaporation exceed those of precipitation.

• Salinities are lower in equatorial regions where precipitation is abundant.

• Salinities of 32 or 33 ppt occur in polar regions where seawater is diluted by melting sea ice.

• The lowest salinities often occur where large rivers empty into the oceans.


Seawater


Sources of Sea Salt

Seawater

– Geological evidence indicates that the salinity of ancient seas was not much different from that of today’s oceans.

– The proportion of magnesium in the calcium-carbonate shells of some marine organisms depends on the overall salinity of the water in which the shells form.

– Present-day shells contain about the same proportion of magnesium as similar shells throughout geologic time.


Sources of Sea Salt

Seawater

– The sources of sea salts has remained the same over time.

• Chlorine and sulfur dioxide dissolve in water and form the chlorine and sulfate ions of seawater.

• The weathering of crustal rocks generates most of the other abundant ions in seawater.

• These ions are then flushed into rivers and transported to oceans.


Removal of Sea Salts

Seawater

– Salts are removed from the ocean at the same rate as they are added.

– The removal of sea salts involves several processes.

• Some sea salts precipitate from seawater near arid, coastal regions.

• Salty spray droplets from breaking waves are picked up by winds and deposited inland.

• Marine organisms remove ions from seawater to build their shells, bones, and teeth.


Removal of Sea Salts

Seawater

Physical Properties of Seawater• Freshwater has a maximum density of 1.00 g/cm3.

Seawater

• Seawater is denser than freshwater because salt ions are heavier than water molecules.

• The density of seawater ranges from about 1.02 g/cm3 to 1.03 g/cm3 depending on its salinity and temperature.

• Because salt ions interfere with the formation of hydrogen bonds, the freezing point of seawater is –2°C.

Physical Properties of Seawater

Absorption of Light

Seawater

– Water absorbs light, which gives rise to another physical property of oceans—they are dark.

– In general, light penetrates only the upper 100 m of seawater.

– Red light penetrates less than blue light.

– Light sufficient for photosynthesis exists only in the top 100 m of the ocean.

Ocean Layering• Ocean surface temperatures range from –2°C in

polar waters to 30°C in equatorial regions, with the average surface temperature being 15°C.

Seawater

• Ocean water temperatures decrease significantly with depth.

Ocean Layering• A typical ocean

temperature profile plots changing water temperatures with depth.

Seawater

Ocean Layering• Based on temperature variations, the ocean can

be divided into three layers.

Seawater

– The first layer is a relatively warm, sunlit, surface layer some 100 m thick.

– The thermocline is a transitional layer which is characterized by rapidly decreasing temperatures with depth.

– The bottom layer is cold and dark with temperatures near freezing.

Ocean Layering

Seawater

Ocean Layering• Both the thermocline and the warm surface layer

are absent in polar seas, where water temperatures are cold from top to bottom.

Seawater

• In general, ocean layering is caused by density differences of warm and cold water.

Water Masses• Cold water migrates toward the equator as a cold,

deep water mass along the ocean floor.

Seawater

– To start, sea ice that forms in the polar regions does not incorporate salt ions into growing ice crystals, causing them to accumulate beneath the ice.

– As the cold water beneath the ice becomes saltier and denser than the surrounding seawater, it sinks.

– Surface currents in the ocean also bring relatively salty midlatitude or subtropical waters into polar regions where they cool and sink.

– The dense, salty water then migrates toward the equator as a cold, deep water mass along the ocean floor.

Water Masses• Three water masses account for most of the deep

water in the Atlantic Ocean.

Seawater

1. Antarctic Bottom Water forms when antarctic seas freeze during the winter and water temperature drops below 0°C.

2. North Atlantic Deep Water forms in a similar manner offshore from Greenland.

3. Antarctic Intermediate Water forms when the relatively salty waters of the Antarctic Ocean decrease in temperature during winter and sink.

Water Masses

Seawater

• The Indian and Pacific Oceans contain only the two deep antarctic water masses.

Section Assessment

1. By what processes are salts removed from seawater?

Seawater

Salts are removed from seawater through the formation of evaporites, sea spray that is carried inland by wind, and biological processes.

Section Assessment

Seawater

2. What is a thermocline?

A thermocline is a transitional layer between warm surface waters and cold bottom waters in a body of water that is characterized by rapidly declining temperatures with depth.

Section Assessment


Seawater

______ North Atlantic Deep Water overrides Antarctic Bottom Water.

______ Photosynthesis can occur to a depth of 200 m.

______ Sodium is the most prevalent ion in seawater.

______ Salt water is always denser than freshwater, regardless of temperature.

true

false

false

true

– wave

– crest

– trough

– breaker

Objectives• Describe the physical properties of waves.

• Explain how tides form.

• Compare and contrast various ocean currents.

Vocabulary

Ocean Movements

– tide

– density current

– surface current

– upwelling

Ocean Movements• A wave is a rhythmic movement that carries

energy through space or matter, such as ocean water.

Ocean Movements

• As an ocean wave passes, the water moves up and down in a circular pattern and returns to its original position.

Wave Characteristics• A crest is the highest point of a wave.

Ocean Movements

• A trough is the lowest point of a wave.

• The vertical distance between crest and trough is the wave height; the horizontal crest-to-crest distance is the wavelength.

Wave Characteristics• The wavelength determines the wave base,

which is the depth to which the wave disturbs the water.

Ocean Movements

• Wave speed increases with wavelength.

Wave Characteristics

Ocean Movements


Wave Height

Ocean Movements

– Wave heights depend upon three factors: wind speed, wind duration, and fetch.

– Fetch refers to the expanse of water that the wind blows across.

– Large storm waves can be much higher than average.


Breaking Waves

Ocean Movements

– Ocean waves begin to lose energy and slow down near the shore because of friction with the ocean bottom.

– As the water becomes shallower, incoming wave crests gradually catch up with the slower wave crests ahead.

– Breakers are waves where the crests collapse forward when the wave becomes higher, steeper, and unstable as it nears shore.


Breaking Waves

Ocean Movements

Tides• Tides are the periodic rise and fall of sea level.

Ocean Movements

• The highest level to which water rises is known as high tide, and the lowest level is called low tide.

• Because of differences in topography and latitude, the tidal range—the difference between high tide and low tide—varies from place to place.

• Generally, a daily cycle of high and low tides takes 24 hours and 50 minutes.

Tides

Ocean Movements

Differences in topography and latitude cause three different daily tide cycles. Areas with semidiurnal cycles experience two high tides per day. Areas with mixed cycles have one pronounced and one smaller tide each day. Areas with diurnal cycles have one high tide per day.

Causes of Tides• The basic causes of tides are the gravitational

attraction among Earth, the Moon and the Sun, as well as the fact that gravitational attraction decreases with distance.

Ocean Movements

• Both Earth and the Moon orbit around a common center of gravity.

• As a result, Earth and the Moon experience gravitational and centrifugal forces that generate tidal bulges on opposite sides of Earth.

Causes of Tides

Ocean Movements

Causes of Tides

The Sun’s Influence

Ocean Movements

– The gravitational attraction of the Sun and Earth’s orbital motion around the Sun also generate tides.

– Lunar tides are more than twice as high as those caused by the Sun because the Moon is much closer to Earth.

– Solar tides can either enhance or diminish lunar tides.

• Spring tides occur when the Sun, the Moon, and Earth are aligned, causing high tides to be higher than normal and low tides to be lower than normal.

• During neap tides, high tides are lower and low tides are higher than normal.

Causes of Tides

The Sun’s Influence

Ocean Movements

Ocean Currents• A density current moves slowly in the deep

ocean and is caused by differences in the temperature and salinity of ocean water, which in turn affect density.

Ocean Movements

• Surface currents are wind-driven currents that affect mainly the upper few hundred meters of the ocean and can move as fast as 100 km per day.

• Surface currents follow predictable patterns influenced by Earth’s global wind systems.

Ocean Currents

Gyres

Ocean Movements

– The continents deflect ocean currents to the north and south causing closed circular current systems, called gyres, to develop.

– There are five major gyres: the North Pacific, the North Atlantic, the South Pacific, the South Atlantic, and the Indian Ocean.

– The parts of all gyres closest to the equator move towards the west as equatorial currents until they are deflected toward the poles by a landmass.

– After cooling in the polar regions, the current, deflected by landmasses, moves back toward the equator.

Ocean Currents

Ocean Movements

Upwelling• Upwelling is the upward motion of ocean water.

Ocean Movements

• Areas of upwelling exist mainly off the western coasts of continents in the trade-wind belts.

• Upwelling waters are rich in nutrients, which support abundant populations of marine life.

Upwelling

Ocean Movements

Section Assessment

1. Match the following terms with their definitions.

___ crest

___ trough

___ tide

___ upwelling

___ breakers

Ocean Movements

A. the upward motion of ocean water, caused by an offshore wind

B. the lowest point of a wave

C. the periodic rise and fall of sea level.

D. the highest point of a wave

E. waves that become higher, steeper, and unstable which causes their crest to collapse

D

B

C

A

E

Section Assessment

2. Why are lunar tides much higher than solar tides?

Ocean Movements

Lunar tides are more than twice as high as solar tides because the Moon is much closer to Earth.

FL: SC.E.1.4.1

Section Assessment

Ocean Movements


______ Gyres rotate in a counterclockwise direction in the northern hemisphere.

______ The water in a wave moves steadily forward.

______ Wave speed increases with wavelength.

______ Spring and neap tides alternate every four weeks.

false

false

true

false

Chapter Resources Menu

Chapter Resources Menu

Study Guide

Section 15.1

Section 15.2

Section 15.3

Chapter Assessment

Image Bank

Section 15.1 Main Ideas• Oceanography is the scientific study of Earth’s oceans.

Oceanographers use sonar, satellites, and submersibles, among other tools, to explore the ocean.

• Earth’s first oceans likely formed more than 4 billion years ago. Some water may have come from impacting comets or from deep within Earth’s interior. Scientists theorize that water from within Earth’s interior was released by volcanism.

• Approximately 71 percent of Earth’s surface is covered by oceans. The major oceans are the Pacific, Atlantic, Indian, Arctic, and Antarctic.

Section 15.1 Study Guide

Section 15.2 Main Ideas• Seawater contains 96.5 percent water and 3.5 percent

dissolved salts. The average salinity of seawater is 35 ppt. The salinity of the ocean remains constant because salts are removed from the ocean at the same rate as they are added.

• Ocean surface temperatures range from –2°C in polar waters to 30°C in equatorial waters. Seawater density changes with changes in salinity and temperature.

• Ocean water temperatures decrease with depth. The ocean can be divided into three layers: the surface layer, the transitional thermocline, and the bottom layer.


Section 15.3 Main Ideas• Ocean waves are generated by wind. Water in a wave

moves in a circular motion but does not move forward. When waves reach shallow water, friction with the ocean bottom slows them, and they become breakers.

• Tides are caused by the gravitational attraction among Earth, the Moon, and the Sun. Lunar tides are twice as high as solar tides.

• Density currents are deep currents generated by salinity and temperature differences. Wind-driven surface currents affect the upper few hundred meters of the ocean. Upwelling occurs when winds push surface water aside and the surface water is replaced by cold, deep water.


1. Approximately how much of Earth’s surface is covered by oceans?

a. 51 percent c. 71 percent

b. 61 percent d. 81 percent

Multiple Choice

Chapter Assessment

Because most landmasses are located in the northern hemisphere, oceans cover only 61 percent of the surface there. However, 81 percent of the southern hemisphere is covered by water.

2. Of the areas listed below, which generally has the lowest ocean salinity?

a. subtropical regions c. temperate regions

b. tropical regions d. polar regions

In the polar regions, seawater is diluted by melting sea ice. On a localized level, the lowest salinities often occur where large rivers empty into the oceans.

Multiple Choice

Chapter Assessment

Multiple Choice

3. Which term below best describes the tide when the Sun, the Moon, and Earth form a right angle?

a. spring tide c. high tide

b. neap tide d. low tide

Chapter Assessment

During a neap tide, high tides are lower than normal and low tides are higher than normal. During a spring tide the solar and lunar tides are aligned, causing high tides to be higher than normal and low tides to be lower than normal. Spring and neap tides alternate every two weeks.

Multiple Choice

4. What is the average ocean surface temperature?

a. 8ºC c. 15ºC

b. 12ºC d. 18ºC

Chapter Assessment

Surface temperature of Earth’s oceans varies between –2ºC in the polar regions to 30ºC in equatorial regions.

Multiple Choice

5. Which of the following is the most prevalent ion in seawater?

a. chloride c. sodium

b. sulfate d. magnesium

Chapter Assessment

Chloride has a concentration of 19.35 ppt in seawater. It is followed by sodium (10.76 ppt), sulfate (2.71 ppt), and magnesium (1.29 ppt).

Short Answer

6. What are the three factors that determine wave height?

Chapter Assessment

The three factors that determine wave height are wind speed, wind duration, and fetch. Fetch refers to the expanse of water that the wind blows across.

Short Answer

7. What are the three basic ocean layers and are they distributed evenly throughout the oceans?

Chapter Assessment

The three basic ocean layers are the surface layer, the thermocline, and the bottom layer. They are not distributed evenly. Both the thermocline and surface layer are absent in polar seas, where water temperatures are cold from top to bottom.

True or False


______ Oceanography is usually considered to have started with the Meteor expedition.

______ Some water molecules in the atmosphere are

continually being destroyed by ultraviolet radiation from the Sun.

______ Blue light does not penetrate as far as red light

in the ocean.

______ The Moon and Earth revolve around a common

center of gravity.

Chapter Assessment

false

true

false

true

Image Bank

Chapter 15 Images

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