Ppt ch13

Chapter 13: Oceans and Coastlines
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1. Our Changing Oceans
2. Ocean Basins
3. Ocean Waters
4. Oceanic Circulation
5. Tides
6. Wave Action
7. Shoreline Features
8. Shoreline Protection

The Good Earth/Chapter 13: Oceans and Coastlines
About 71% of Earth is covered with seawater. The Oceans
were mostly in place by ~4 billion years ago. They are the
final frontier for research on Earth.
Our Changing Oceans

Our Changing Oceans
Elephant seal as researcher – sensors glued to her back record
information about temperature and salinity of the surface waters. This
information cannot be gathered through satellites. Elephant seals migrate
from California to Alaska and back, and dive as deep as 600 meters.

Our Changing Oceans
Temperature
vs. depth for
NE Pacific
ocean. The
range of
temperatures
reflects
different
locations
along the
seal’s journey.
4,000 marine animals from 20
species collect ocean data.

Our Changing Oceans
• Oceans are
dynamic! Water is
continually in
motion. Oceanic
and atmospheric
circulation patterns
move heat around
and strongly
influence climate.
• Coastlines are also
dynamic, advancing
and retreating
depending on the
balance of erosion
and deposition.
A storm at Nag’s Head, NC

Our Changing Oceans
• How do oceans/coastlines change?
− Coastlines can advance or retreat
− Short term, the position of the coastline can change
depending on daily tides and seasonal variations in
stream flow
− Climate cycles measured over decades, centuries,
or millennia can show rises and falls in sea level
− Tectonic cycles occurring over thousands to
millions of years can revitalize coastlines through
uplift
− Humans can influence oceans and coastlines as
well, and be strongly affected by oceans and their
weather (e.g. hurricanes)
− More than ¼ of the U.S. population lives along the
Atlantic and Gulf coasts The Good Earth/Chapter 13: Oceans and Coastlines
Malibu, Ca

Our Changing Oceans Self Reflection
Survey
Answer the following questions as a means of uncovering what
you already know about oceans and coastlines:
1.How have you interacted with the world’s
oceans, either directly or indirectly?

Survey
2. Would you prefer to live along a coast or
farther inland away from the ocean? What
are the advantages and disadvantages of
living along the coast?

Survey
3. Henry Boston identified three elemental
sounds of nature: the sound of the ocean
on a shore, the rain, and the wind in woods.
Can you suggest three more?

Go back to the Table of Contents
Go to the next section: Ocean Basins

Bathymetry (depth) of the Ocean Floor
− From what you learned about plate tectonics would you expect
the depths to be the same throughout the world’s oceans?
• The depth of the ocean (surface to floor) varies from zero meters (along
the coast) to a maximum of nearly 11 km (7 miles) along the Mariana
trench.
• Mt. Everest would sit in the trench with over 2,000 meters to spare!
(More than 1500 people have stood atop Everest – only 2 have visited
the deepest region of the ocean floor).
• Average land elevation is less than 1 km, but average ocean depth is
3.8 km (2.3 miles).
• Volume of water in the oceans is nearly 10 times the volume of dry land
that lies above sea level.
• If erosion leveled the continents, all the eroded material would fit in the
ocean basins with room to spare!

Depth of the Ocean Floor
• The elevation of the ocean surface varies
because the elevation of the ocean floor varies
• Bathymetry = the measurement of the depth to
the ocean floor, and the mapping of its features
− Data from ships and submarines are combined with
satellite data to reveal the topography of the ocean
floor
− Ocean floor has mountains, valleys, and plains
similar to those on land
• Masses of rock on the sea floor exert
gravitational pull on the water causing it to
pile up and form a mound on the ocean
surface

Sea Level is assumed to be zero meters
Sea Level changes are due to changes in the shape of the ocean basins,
or long-term climate changes that trap water in ice caps or cause ice caps
to melt.
The sea surface has bumps and low points – a satellite
measures the difference in height between the “bump” over
a volcano and the surrounding ocean. Radars on satellites
are used to measure variations in gravity, revealing ocean
floor topography.

The Four Major Depth Zones = Continental shelf, Abyssal
plain, Oceanic ridge, Oceanic trenches
Passive margin zones: Continental shelf,
Continental slope, Continental rise, Abyssal
plain
Active margin zones: Continental
shelf, Continental slope, Trench,
Abyssal Plain

Zone 1 - The Continental Shelf
• The shallow ocean floor adjacent to the
continent
• Submerged continental crust that slopes
away from coast
• Maximum depth is a few hundred meters
• Wide when adjacent to passive margins,
narrow when adjacent to active margins
• The width of the shelf decreases as sea
level falls and increases as sea level rises

Depth of the Ocean Floor Checkpoint
13.1
On the following map, identify three active
continental margins and three passive continental
margins. (Don’t worry about the x-y line)

During last N.
Hemisphere glaciation
when sea level
dropped, the
continental shelf off the
coast of New Jersey
was exposed. The
Hudson River cut a
deep, narrow canyon
into the exposed shelf
on its way to the lower
sea level. The canyon
was later submerged
when sea level rose.

Zone 2 - The Abyssal Plain
• Continental Slope and Rise are the transition to the
abyssal plain
- Rapid deepening of the ocean (continental slope) leads to a gentler
slope (continental rise) that ends at the abyssal plain
- The continental slope is marked by a rapid deepening of the ocean (couple
thousand meters)
- Continental rise is where sediments swept off the slope accumulate
• Abyssal Plain = deep ocean floor
• Over 4 km deep and are some of the flattest portions of
Earth’s surface
• Covered by layers of very fine sediment
• May be dotted by seamounts (underwater volcanoes)

Zone 3 - The Oceanic Ridge
• The oceanic ridge system is a submarine mountain chain that can be traced
around the world!
• Ocean floor rises from the abyssal plain to the ridge
• 90% of Earth’s volcanic activity happens at ocean ridges
• Doesn’t heat the water much (rapidly dissipates)
• Depth is ~3 km above ridge crest
• Central valley beyond ridge crest – region of submarine hot springs (hot
smokers). They are home to some strange life!
A white crab and
tubeworm colony
found near a hot
smoker

Zone 4 - The Oceanic Trench
• Active continental margins, where two plates converge, form an
oceanic trench near the subduction zone
• Narrow and deep – deepest places on Earth!
• Mark the place where oceanic lithosphere descends into the mantle
• 7 to 11 km (4 to 7 miles) deep

Depth of the Ocean Floor Checkpoint
13.3
Note the X-Y line on the world map (below left). Which of the
profile views (below right) most accurately models the
bathymetry of the ocean floor along that line?
Hint: Think about where there is
an active margin vs. a passive
margin.

Go to the next section: Ocean Waters

Ocean Waters
• Where did our oceans come from?
− Early Earth was a hostile, hot mass of nearly molten rock
− Violent volcanic eruptions put gases, including water vapor, into
the air
− As Earth cooled this water vapor condensed into liquid water
− The more the planet cooled, the more water could collect in
hollows (“baby” oceans that grew into our present oceans)
− Although the water in the oceans has been around for ~4 billion
years, the present ocean basin configuration is the result of plate
tectonics, and no ocean basin is older than about 200 million
years old
− Even now, oceans and seas continue to grow or shrink as plates
diverge or converge

Ocean Waters: Water Chemistry
The oceans are “salty” because seawater contains dissolved salts and
minerals
Most of the dissolved solids in seawater is common salt (NaCl)
Salinity = the measure of the concentration of salt in seawater
More salt = higher density
Q: What variables
might influence
what parts of the
ocean (locations
around the globe)
are saltier than
others?

Ocean Waters: Salinity
Salinity is
influenced by:
-Temperature
-Mixing caused
by currents
-Freshwater
input from rain,
streams, and
melting ice
Salinity is
highest where
temp is high and
precipitation is
low (evaporation
leaves behind
salts)

Ocean Waters
Q: Why is salinity not highest at the
equator?
A: More precipitation occurs over equatorial
regions, diluting the waters there and
thereby reducing salinity.
Q: Why might the salinity near the
Hawaiian islands be only 0.2 %
different than the salinity off the coast
of Antarctica?
A: Ocean currents are efficient mixers and
even out some salinity differences in the
oceans.

Ocean Waters Checkpoint 13.5
Examine the map of mean
salinity for the Indian
Ocean. Explain why
salinity values are lower for
the tropical Bay of Bengal
(east of India) than for the
cold waters of the
Southern Ocean just north
of Antarctica? Why do you
think salinity is so high in
the Red Sea (small red
strip between Africa and
Saudi Arabia)?

Ocean Waters: Salinity
Salinity of the oceans also varies with depth
Rapid
decrease
in salinity
with
depth in
upper
500
meters
Rapid change in salinity with depth = halocline
Deeper waters not affected by surface processes
that change salinity (evaporation and stream flow)
N-S profile
through Pacific
Ocean (150°W)

Ocean Waters: Temperatures
Temperature varies according to latitude
Ocean temperatures
are affected by:
- Solar insolation
- Ocean currents
Temperatures are
highest where solar
energy is highest.

Water has a high specific heat (amount of
thermal energy required to raise the
temperature of 1 gram of material by 1°C).
-The temperature of a material with a high specific
heat will not rise as rapidly as one with a low
specific heat.
-Water can absorb a lot of thermal energy without displaying
much of a change in temperature.
Why is it important that water has a high heat
capacity?
-Water can absorb, store, move, and release a lot
of heat energy.
-This is of major importance to global climate patterns.
The density of water decreases with increasing temperature

Ocean Waters Checkpoint 13.7
The specific heat of the water in the
oceans is about 4 times that of the
rock and soil on the continents. In
addition, water in the oceans moves,
while rock and soil are effectively
stationary. What are the implications
of these observations for differences in
maximum and minimum temperatures
of the oceans and continents?

Ocean Waters
• Shallow layers of ocean water:
− Relatively warm, warmed by solar radiation
− Relative uniform temperature as water is mixed by
currents
Warm water is less dense than
cold water
Below 4°C this changes – the
density of really cold water
decreases, especially when it
goes from liquid to solid form
Thermocline = The depth zone where temperature
decreases most rapidly

Temperature of the oceans also varies with depth
Rapid
decrease
in temps
with depth
in upper
500
meters
Rapid change in temperature with depth = thermocline N-S profile
through Pacific
Ocean (150°W)

Ocean Waters: Density
Uniform increase in pressure with depth slightly increases density of
the underlying water
The third factor that affects density - pressure
Salinity, temperature,
and pressure combine
to create density profile.
Pycnocline = rapid
increase in density from
200 – 1,000 meters
depth.
Density is uniform
below the pycnocline.
Ocean water - 3 main
vertical density layers:
surface (2%), middle
(18%), and bottom
(80%).

Go to the next section: Oceanic Circulation

Oceanic Circulation
Ocean water is in constant motion!
Circular patterns (gyres) of ocean currents.

Oceanic Circulation: Currents
• Winds move ocean water
− Friction between wind and surface
water
− Ocean currents follow prevailing
wind direction except where the
current encounters a barrier
(e.g. landmass)
− Only about 10% of world’s ocean
water is moving in surface currents
Narrow, high temperature
Gulf Stream

Oceanic Circulation: Currents
• Circulation patterns in atmosphere
generate gyres
− Clockwise in N Hemisphere,
counterclockwise in S Hemisphere
− Water takes months to years to
complete a gyre circuit
− Fast-flowing boundary currents at
western extents of gyres redistribute
warm tropical water toward the
poles (e.g. Gulf Stream, Brazil)
− Eastern portions of gyres carry
colder water from high latitudes
toward equator (e.g. Canary,
Benguela)

Oceanic Circulation Checkpoint 13.9
A shipment of rubber elephants falls overboard in the northern Pacific at
location A on the map below. What path do the elephants follow? (Refer
to figure 13.15)
A. A-G-B-F-E-A
B. A-E-C-G-A
C. A-G-C-E-A
D. A-E-F-B-G-A

Oceanic Circulation
• Coriolis Effect: Atmospheric
and oceanic circulation
patterns deflected to right in
N Hemisphere and to left in S
Hemisphere
• Earth rotates from west to
east
• Objects near equator are
moving faster than those
near the poles (more
distance to cover in a day’s
rotation)
• The planet beneath the
circulating wind/water moves
its position, leading to the
deflection
Imagine you are in Panama City, FL.
At noon you fire a rocket directly
north towards Columbus, OH. The
rocket has a northward velocity, but
also has a faster easterly velocity
due to Earth rotating east. The
rocket will land east of the city of
Columbus – the apparent deflection.

How would the deflection of ocean currents be
altered in the Northern Hemisphere if Earth
rotated from east to west (instead of from west
to east)?
a) Currents stay the same, deflect right of their
course
b) Currents stay the same, deflect left of their course
c) Currents switch directions, deflect right of their
course
d) Currents switch directions, deflect left of their
course

Oceanic Circulation
Continents can affect ocean
circulation patterns
• Closure of Isthmus of
Panama influenced
circulation patterns in
Atlantic
− Western currents forced
N
− Strengthened gulf
stream
− Warmer waters into N
Atlantic
− Raised temperatures in
Europe
− Winters milder in
Europe and N. U.S.

Antarctica used to be mostly free of ice
• About 34 million years ago ice growth was triggered
− Separation of S. America and Australia from Antarctica
− Before this occurred, warm tropical waters moved south
and warmed Antarctica
− The separation of Antarctica and South America opened
up the strong currents in the Southern Ocean
− Isolates Antarctica from moderating ocean currents
Oceanic Circulation

Oceanic Circulation: Thermohaline
Circulation
Gulf Stream
• Carries high-salinity, warm waters from central Atlantic to higher
latitudes
• Water slowly cools as it travels N
• Cold, salty water sinks to the bottom of N Atlantic near Greenland and
Iceland
• Sinking water is then carried southward along bottom of the Atlantic
(NADW)
• Reaches Antarctica and is diverted eastward to the Indian and Pacific
• Deep current eventually comes up in N Indian and Pacific Oceans
(upwelling) – brings nutrients to surface waters
The pattern of deep currents is termed thermohaline
circulation (driven by both salinity and temperature)

A fish tank is filled with water at room temperature. Cold water is added on
one side of the tank and warm water is added on the other side. The water
at each temperature is dyed a different color to show its movement.
Predict what will happen when warm water and cold water are added to
the tank simultaneously. Briefly describe your prediction and sketch it in
the drawing of the tank below.

Global Thermohaline Circulation

Oceanic Circulation: ENSO
El Niño and La Nina: The Earth system in action
Normal Year
Pacific ocean waters heated
Trade winds blow warm
water west
Cold upwelling occurs off
coast of SA
El Niño Year
Western trade winds diminish
Warm water remains in Pacific
Heavy rains occur in SA
Surface salinity decreases, reducing
upwelling
Droughts in western Pacific
La Nina Year
Cold conditions dominate
Droughts in SA, western US
Severe weather in western
Pacific

Go to the next section: Tides

Phases of the Moon
Moon orbits Earth
every 27.3 days
New moon: Moon
between Earth
and sun
Full moon: Earth is
between Sun and
moon

Tides
Tides = changes in the sea surface height caused by the
gravitational attraction of the moon (and a bit by the sun)
• a) Spring tides – largest tidal bulges, highest tides
• b) Neap tides – smallest tidal bulges, lowest tides
Sun and moon exerting pull on the Earth in
same direction. Occur during New Moon.
Sun and moon exerting pull on the Earth in
different directions.

Tides Checkpoint 13.13
What would happen to spring tides if the
moon were farther away from Earth?
a)Tides would be higher
b)Tides would be lower
c)No change to spring tides

Tides
Because the Earth rotates faster than the moon orbits, the
location of the tidal bulge changes
• The moon is not always over the same spot on Earth
• Moon is essentially stationary while Earth rotates on its axis
• Imagine tidal bulges as stationary as Earth rotates below them
• A coastal site would rotate below two tidal bulges (high tides)
on opposite sides of the Earth each day
• It would also pass through two minima (low tides)
(Equal, but opposite, tidal bulges on the side of Earth away from Moon
– due to a balance of forces associated with gravitational attraction of
moon, rotation of earth-moon system about a common center of mass
called barycenter, and rotation of Earth on its axis)

Tides
Depending on the
position of the mood
relative to Earth, and
the latitude of a
coastal site, the two
daily tides may be
very similar
(semidiurnal) or varied
(mixed).
In panel b, notice that
an equatorial coastal
city would have a
semidiurnal tide
pattern, while at mid
latitude the pattern
would be mixed (very
high on the right side
of the image, and low
on the upper left side).

Tides
a) semidiurnal
b) mixed
c) diurnal

Which tidal pattern is represented by the tide
data for San Diego, California?
a)Semidiurnal
b)Diurnal
c)Mixed

Many planets have multiple moons. Discuss how the tides would be
affected if Earth had two moons (A and B), each half the size of the current
moon, in the following two scenarios:
a) Assume the two moons followed the current orbit of the
moon and were located on opposite sides of Earth (half an
orbit apart; e.g., in the positions of the new moon and full
moon).
b) Assume the two moons followed the current orbit of the
moon and were located one quarter of an orbit apart (e.g., in
the positions of the new moon and the first quarter moon).
Draw diagrams showing the locations of the moons relative to the Earth and
the sun and illustrating how each scenario would change a typical
semidiurnal pattern recorded on a tide gauge.

Go to the next section: Wave Action

Wave Action: Open Ocean
In the open ocean water simply bobs up and down. The
wave shape (waveform) moves while the water particles
follow a circular path and remain in place.

Wave Action: Open Ocean
• Wave size, speed, and direction are controlled by winds
• The waves we see in the ocean are the result of wind energy
transferred to surface water
Wave action affects
only surface waters.
Motion decreases
downward to a depth
equal to about ½ of the
wavelength called the
wave base.
The deeper the wave
base, the more volume
of water involved in the
wave.

Waves in the open oceans:
What do you observe?

Wave Action
• Wind generated waves increase in size with increased wind
speed
− Wind speed and distance over which wind blows determine the
frictional force, and ultimately the wave height
− Large waves come from high velocity, steady winds blowing
across a wide area with no obstructions
Which ocean do you think has consistently taller waves
– the Atlantic or the Pacific? Why?
Where do you think the largest waves (5-10 m) on Earth
are found?
Southern Ocean – no continents to interrupt the
distance over which winds blow.

Wave Action
As a wave
approaches
shore and
shallower water
it is slowed by
friction, its
length
decreases, and
it becomes taller
and steeper.
Wave eventually
collapses due to
over-steepening
(breaker).
Water actually
moves forward
here.

Wave Action Checkpoint 13.17
At which location on the following diagram would
the waves begin to break farthest from the
beach?

Wave Action
a. Path of Hurricane Katrina. 42040 is a
station that recorded wind speed and
wave height.
b. Average wind speed for 10 minute intervals. c. Significant wave
height. Notice correspondence between highest waves and fastest
wind speeds.

Wave Action
Rip Currents – Narrow currents of water flowing through gaps in
sandbars lying just offshore.
Rip currents are caused by variations in the surf zone such as
sandbars and channels.
Do you see a location in the
picture at right that might be
dangerous if you were
swimming there? Do you
think you could see it from
the beach?
Rip currents cause ~100
deaths in the U.S. each year
If you get caught in one – let
it sweep you out past the
structure that is causing it.
Once past it, swim parallel to
the beach and then back
toward shore.

Wave Action
• Irregularities in the
shoreline or
changes in seafloor
can change shape
and direction of the
waves
• Can cause bending
of the waves toward
the shore
(refraction)

Wave Action: Turning waves into energy
• Ocean waves are actually
energy moving through the
oceans
• If that energy could be
harnessed, it would be clean
and renewable
What is the best location to build an
ocean wave-driven power
generation facility? What problems
might you face?

Go to the next section: Shoreline Features

Shoreline Features
Shorelines are constantly changing as materials are eroded,
transported and deposited through a process known as the
sediment budget.

Shoreline Features
What do waves do to coastlines?
• Cause erosion (wearing away headlands and filling in
bays – straightens out coastline)
• Transport material
• Deposit sand and other materials
Twelve homes in Pacifica,
CA were condemned when
the cliff retreated 33 feet.

Shoreline Features
Erosion rates of
the coastlines
along the
Atlantic shore
and Gulf coast
are 3.3 ft per
year on average
Erosion is worst
on loose,
unconsolidated
sediments, and
can be
accelerated by
surges caused
by storms

Shoreline Features
Shorelines can also be experiencing deposition
• Shoreline grows in width with deposition of sediment
• Head on currents carry sediment onto and off the beach, and may
deposit sand in sand bars off shore during storms
• Longshore currents transport sediment parallel to the beach in the
surf zone
Sand was moved left to right during a storm.

Shoreline Features
• Spit – sand bar partially
blocking a landform
• Baymouth Bar – sand bar that
completely blocks a channel
The bay at Puget Sound,
Washington. This narrow spit
may become a baymouth bar.

Streams and Coastal Systems Checkpoint 13.24
Place the terms/phrases in the correct
location on the Venn diagram.
1. Erosion creates underwater channels.
2. Source: continental interior
3. Source: offshore sandbar
4. Sand deposited in bars
5. Erosion more pronounced in winter
6. Occur at my range of elevation
7. Occur at sea level
8. Erosion by wave action
9. Similar erosion rates
10. Longshore current
11. Mix of grain sizes
12. Uniform grain sizes

Go to the next section: Shoreline Protection

Shoreline Protection
Natural Features that protect coastal residents of
Florida from erosion:
-Tall dunes behind beaches protect against large storms
-Wide, stable beaches absorb wave energy
-Exposed offshore sand bars absorb the force of breaking waves
These features are not found at all beaches.
Humans can erect artificial barriers to help slow
erosion, but these features may speed up
erosion in other coastal locations.

The sediment budget = the balance between material deposited
on the shore and material eroded from the shore.
Humans can influence the sediment budget, and coastline features, by
their actions.
Damming on major rivers can result in sediment starvation because
sediment that would have been deposited along the shoreline is
trapped upstream.
Humans can also build structures to try to combat dangerous erosion
processes
Seawall - Rock
wall built to try
and slow
erosion of a cliff
north of
Monterey, Ca.

Groins – wall-like structures built perpendicular to
the shoreline as barriers to longshore currents
• Causes deposition on upcurrent side, but erosion on
downcurrent side

Breakwaters – barriers built offshore to protect
part of the shoreline
• Slow the waves and allow the beach to grow behind them
Unprotected parts
of the shoreline
often erode more
quickly.

Shoreline Protection Checkpoint 13.25
Compare and contrast seawalls and
breakwaters.

Shoreline Protection Checkpoint 13.26
Examine figure 13.31
and explain why the
shoreline
erosion/deposition
process at the site of
Cape Hatteras
required the
lighthouse to be
moved.

Oceans and Coastlines Concept Map
Complete the concept
map to evaluate your
understanding of the
interactions between
the earth system,
oceans and
coastlines.
Label as many
interactions as you
can using information
from this chapter.

The End

Ppt ch13

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