The Oceans
The Oceans
Oceanography is the scientific study of Earth’s
oceans, including its inhabitants, it’s physical and
chemical properties.
In the late 1800s, the British Challenger
expedition became the first research ship to
use relatively sophisticated measuring devices
to study the oceans.
It studied ocean currents, temperature,
sediments, and topography.
The Oceans
Modern Oceanography
• In the 1920s, the German research ship Meteor
used sonar for the first time to map the seafloor
features, the mid-Atlantic ridge, of the South
Atlantic Ocean.
Modern Oceanography
• 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.
- 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.
How SONAR works
Side scanning SONAR
The Oceans
Modern Oceanography
– Today we can use SONAR and satellites to study
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.
Submersibles
The Oceans
Origin of the Oceans
Where did the water come from?
– 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.
The Oceans
Origin of the Oceans
Volcanism
– 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.
The Oceans
Distribution of Earth’s Water
“The Blue Planet”
– Approximately 71 percent of
Earth’s surface is covered by
oceans.
– Because most landmasses are
in the northern hemisphere,
oceans only cover 61 percent
of the surface.
– Water covers 81 percent of
the southern hemisphere.
The Oceans
Distribution of Earth’s Water
• The oceans contain 97 percent of all of the
water found on Earth.
• 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.
The Oceans
Distribution of Earth’s Water
• Sea level is the level of the oceans’ surfaces.
– It is currently rising due to melting ice caps.
– Tectonic forces that lift or lower portions of the seafloor
has also affected sea level.
– Sea level has risen and fallen by hundreds of meters in
response to melting ice during warm periods and
expanding glaciers during ice ages.
– We’ll talk more about sea level at the end of the unit
The Oceans
Distribution of Earth’s Water
Major Oceans
– There are four 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 smallest is the Arctic Ocean.
The Oceans
Distribution of Earth’s Water
Major Oceans
The Oceans
Distribution of Earth’s Water
Seas
– 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.
The Oceans
Section Assessment
3. Identify whether the following statements are
true or false.
______
true Oceans contain 97 percent of the water found
on Earth.
______
true Oceans cover 71 percent of Earth’s surface.
______
false The Earth’s major oceans are isolated from
each other by landmasses.
______
false Presently, average global sea level is
decreasing 1 to 2 cm per year.
Seawater
Seawater
• Seawater is a solution of about 96.5 % pure
water and 3.5 % dissolved salts.
• 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
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).
• The total salt content of seawater is, on average,
35 ppt, or 3.5 percent.
• Seawater also contains dissolved gases and
nutrients.
Seawater
Chemical Properties of Seawater
– The actual salinities of the oceans vary.
• Salinities may be decreased by precipitation, runoff,
icebergs melting and sea ice melting. These all add
fresh water into the salty ocean water. (32ppt)
• Salinity can be increased by evaporation. When more
water evaporates than precipitation falls, there is more
water leaving, and thus leaving the salts behind. (37
ppt)
• Salinity can also be increased when sea water freezes
in polar areas. When water freezes, it does not freeze
with the salt in the water. Therefore, the salt is left
behind.
Seawater
Seawater
Chemical Properties of Seawater
Sources of Sea Salt
– 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.
• Volcanoes also contribute.
Seawater
Chemical Properties of Seawater
Removal of Sea Salts
– 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.
Seawater
Sea Surface Temperatures
• Ocean surface temperatures range from –2°C in
polar waters to 30°C in equatorial regions.
• What causes the differences in surface
temperatures?
• The average surface temperature being 15°C.
Water Density
11. Water density is influenced by two factors:
temperature and salinity.
12. Cold water is denser; it sinks to the bottom whereas
warm water is less dense and would rise.
13. The higher the salinity, the denser the water is. It sinks
more.
14. Therefore, the densest combination of water would be
cold &salty water.
15. The differences in temperature and salinity in the ocean
cause vertical layering within the ocean.
16. These differences are also what account for the
currents that exist in the oceans.
Seawater
Ocean Layering
• Ocean water
temperatures
decrease
significantly with
depth.
• 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.
– Ocean water is warmest in the surface zone. (from the
sun’s heat) Then temperature decreases with depth.
– The thermocline is a zone of rapid temperature change.
The temperatures are decreasing with depth.
– The bottom zone is at the bottom. Sunlight never
reaches it and it is very cold, just above freezing.
– 80% of ocean water is found here.
Seawater
Ocean Layering
Seawater
Physical Properties of Seawater
Absorption of Light
– 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 Life Zones
• 1. Ocean life zones are classified based on
sunlight, distance from shore and water depth.
• 2. The zones are: intertidal, neritic, and open-sea.
• 3. The intertidal is where the land and sea meet
and overlap. Sometimes it is underwater and
sometimes it is dry, depending on the tides.
• 4. The neritic zone covers the gently sloping
continental shelf.
• 5. The oceanic zone or open-sea zone reaches
great depths to the ocean floor.
• -The open-sea zone is further divided up into
three sections based on depth.

The photosynthetic zone which is at the top.

The bathyal zone is in the middle
•
The abyssal zone is the bottom.
Open Sea zone
Neritic zone
Photosynthetic zone
Bathyal zone
Abyssal
Ocean Life
• 1. Marine organisms can be classified according
to where they live and how they move.
• 2. Plankton drift with ocean currents. Examples
are: bacteria, algae
Nekton
• Nekton are animals
that swim. Examples
are: fish, squid and
mammals like whales,
seals, etc.
Benthos
Benthos are animals
living in or on the
ocean bottom.
Examples are:
starfish and crabs
Seawater
Water Masses
• Cold water migrates toward the equator as a cold,
deep water mass along the ocean floor.
– 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.
Seawater
Water Masses
• Three water masses account for most of the deep
water in the Atlantic Ocean.
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.
Seawater
Water Masses
• The Indian and Pacific Oceans contain only the
two deep antarctic water masses.
Ocean Movements
• Ocean water is constantly moving in three
ways: waves, tides and currents.
• A wave is a rhythmic movement that carries
energy through space or matter, such as
ocean water.
• As an ocean
wave passes, the
water moves up
and down in a
circular pattern
and returns to its
original position.
1.
Most ocean waves are caused by wind
moving over the water’s surface.
The energy is what is moving. The water is not
moving!
Ocean Movements
Wave Characteristics
• The crest is the top of a wave.
• The trough is the bottom of a wave.
• Wave height is the vertical distance between
crest and trough
• Wavelength is the horizontal distance from
crest-to-crest or trough to trough.
Ocean Movements
Wave Characteristics
Wave Height depends on three things:
– 1. Wind speed
– 2. Length of time the wind has blown
– 3. The distance wind has blown across the surface
Ocean Movements
Wave Characteristics
Breaking Waves
– 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.
Ocean Movements
Breaking Waves
• The surf is the zone where the waves break on
shore.
Ocean Movements
Tides
• Tides are the periodic rise and fall of sea level.
• 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.
• A location usually has two high and two low tides
a day.
Ocean Movements
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.
• 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.
Ocean Movements
Causes of Tides
Ocean Movements
Causes of Tides
The Sun’s Influence
– 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.
Ocean Movements
Causes of Tides
The Sun’s Influence
Ocean Movements
Ocean Currents
• Currents are masses of ocean water that flow
from one place to another.
• Density currents are vertical currents that result
from different densities of water. (Denser water
sinks)
• Surface currents are movements of water that
flow horizontally in the upper part of the ocean’s
surface. They develop due to wind.
• Surface currents follow predictable patterns
influenced by Earth’s global wind systems.
Ocean Movements
Ocean Currents
Gyres
– A gyre is a huge circular surface current.
– There are five major gyres: the North Pacific, the North
Atlantic, the South Pacific, the South Atlantic, and the
Indian Ocean.
– In the N. hemisphere currents more to the right and in
the S. hemisphere they move to the left due to Earth’s
rotation.
Ocean Movements
Ocean Currents
The
Gulf
Stream
Current
Ocean Movements
• Currents moving away from the equator carry
warm water and currents moving away from the
poles carry cold water.
• An upwelling is the rising of cold water from the
deep ocean up to the surface.
• 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.
Ocean Movements
Upwelling
Ocean Movements
Section Assessment
1. Match the following terms with their definitions.
___
D crest
___
B trough
___
C tide
___
A upwelling
___
E breakers
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
Ocean Movements
Section Assessment
3. Identify whether the following statements are
true or false.
______
false Gyres rotate in a counterclockwise direction in
the northern hemisphere.
______
false The water in a wave moves steadily forward.
______
true Wave speed increases with wavelength.
______
false Spring and neap tides alternate every
four weeks.
Chapter Resources Menu
Study Guide
Section 15.1
Section 15.2
Section 15.3
Chapter Assessment
Image Bank
Section 15.1 Study Guide
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 15.2 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 Study Guide
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.
Chapter Assessment
Multiple Choice
1. Approximately how much of Earth’s surface is
covered by oceans?
a. 51 percent
c. 71 percent
b. 61 percent
d. 81 percent
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.
Chapter Assessment
Multiple Choice
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.
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
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.
Chapter Assessment
Multiple Choice
4. What is the average ocean surface
temperature?
a. 8ºC
c. 15ºC
b. 12ºC
d. 18ºC
Surface temperature of Earth’s oceans varies between
–2ºC in the polar regions to 30ºC in equatorial regions.
Chapter Assessment
Multiple Choice
5. Which of the following is the most prevalent ion
in seawater?
a. chloride
c. sodium
b. sulfate
d. magnesium
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).
Chapter Assessment
Short Answer
6. What are the three factors that determine
wave height?
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.
Chapter Assessment
Short Answer
7. What are the three basic ocean layers and are
they distributed evenly throughout the oceans?
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.
Chapter Assessment
True or False
8. Identify whether the following statements are
true or false.
______
false Oceanography is usually considered to have
started with the Meteor expedition.
______
true Some water molecules in the atmosphere are
continually being destroyed by ultraviolet
radiation from the Sun.
______
false Blue light does not penetrate as far as red light
in the ocean.
______
true The Moon and Earth revolve around a common
center of gravity.
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