23.5 The Restless Oceans
Wave action is the
primary means of
erosion along coastlines.
23.5 The Restless Oceans
Exploring the Ocean
How do conditions in the ocean change with
depth?
Light and temperature decrease with depth,
whereas pressure increases.
23.5 The Restless Oceans
Exploring the Ocean
Ocean water is a mixture that includes
dissolved salts and gases.
• Salinity is the proportion of dissolved salts in
water.
• The most abundant salt in ocean water is table
salt, sodium chloride (NaCl).
23.5 The Restless Oceans
Exploring the Ocean
Changes With Depth
Conditions in the ocean change as you move from
the surface to the ocean floor.
• Sunlight decreases with depth in the ocean. The
deep ocean is totally dark.
• Water temperature decreases with depth. Deeper
water is much colder and denser.
• Pressure increases continuously with depth in the
ocean.
23.5 The Restless Oceans
Exploring the Ocean
The Ocean Floor
The continental shelf is a gently sloping plain
that forms an apron of shallow water along the
edges of most continents.
• The continental slope descends more steeply to the
floor of the deep ocean.
• In places, you would see deep canyons cutting
through the continental shelf and slope.
23.5 The Restless Oceans
Exploring the Ocean
The ocean floor itself is a vast, flat plain
dotted with volcanic peaks.
The mid-ocean ridges wind through the ocean
basins, and there are deep trenches along the
edges of some oceanic plates.
23.5 The Restless Oceans
Exploring the Ocean
Kelp forests occur in coastal
waters swept by cold ocean
currents.
Light can penetrate to the
floor of the continental shelf,
allowing the long strands of
kelp to grow in nutrient-rich
waters.
23.5 The Restless Oceans
Ocean Currents
What causes surface currents, density
currents, and upwelling?
Winds blowing across the surface of the
ocean cause the continuous flow of surface
currents.
23.5 The Restless Oceans
Ocean Currents
In upwelling, winds blow warm surface water
aside. This allows cold water from the deep
ocean to rise and take the place of the
warmer water.
Deep ocean currents are caused by
differences in the density of ocean water.
23.5 The Restless Oceans
Ocean Currents
Ocean currents are the patterns of flow in
Earth’s oceans.
Ocean currents are affected by winds, Earth’s
rotation, and the positions and shapes of the
continents.
23.5 The Restless Oceans
Ocean Currents
Prevailing wind patterns drive the ocean’s
surface currents.
23.5 The Restless Oceans
Ocean Currents
Surface Currents
A surface current is a large stream of ocean
water that moves continuously in about the same
path.
Global surface currents reflect the effects of wind
patterns in the atmosphere.
23.5 The Restless Oceans
Ocean Currents
In general, currents of warm water flow away
from the equator along the east side of
continents.
Currents of cold water flow away from the
polar regions along the west side of
continents.
23.5 The Restless Oceans
Ocean Currents
This satellite image of the
Atlantic Ocean shows the
Gulf Stream, which carries
warm water northward
from the Gulf of Mexico
toward the British Isles.
The image has been
enhanced so that red
indicates warmer water
and blue indicates cooler
water.
23.5 The Restless Oceans
Ocean Currents
Deep Currents
Unlike surface currents, deep currents are not
caused by winds.
Denser water results from colder temperatures or
higher salinity.
23.5 The Restless Oceans
Ocean Currents
Because deep ocean currents are affected by
density, they are called density currents.
Density currents are responsible for a slow
mixing of water between the surface and
deeper ocean.
23.5 The Restless Oceans
Ocean Currents
Upwelling
The movement of water from the deep ocean to
the surface is called upwelling.
• Much upwelling occurs along the western coasts of
continents.
• Upwelling brings nutrients from deep in the ocean to
the surface.
23.5 The Restless Oceans
Ocean Currents
Upwelling of deeper ocean water occurs
along some coastlines.
Surface wind
Warm surface water
Cold water upwelling
23.5 The Restless Oceans
Wave Erosion and Deposition
How do waves erode rock and deposit
sediment?
Two physical processes, hydraulic action
and abrasion, are responsible for much
wave erosion.
23.5 The Restless Oceans
Wave Erosion and Deposition
Waves can pound a coastline with a
tremendous amount of energy, so waves are
the major cause of erosion along coastlines.
• On a rocky coast, wave erosion creates cliffs,
arches, caves, and tall rock towers called sea
stacks.
• Over time, wave erosion and deposition work
together to straighten a coastline.
23.5 The Restless Oceans
Wave Erosion and Deposition
A.
A sea cliff with a sea stack and arch in Etretat, France
23.5 The Restless Oceans
Wave Erosion and Deposition
A.
B.
A sea cliff with a sea stack and arch in Etretat, France
A barrier beach in South Carolina
23.5 The Restless Oceans
Wave Erosion and Deposition
A.
B.
C.
A sea cliff with a sea stack and arch in Etretat, France
A barrier beach in South Carolina
A sand spit along the Red Sea in Egypt.
23.5 The Restless Oceans
Wave Erosion and Deposition
How Waves Cause Erosion
The process of hydraulic action occurs when
waves pound on cracks in rocks.
•
•
•
•
First, a wave fills a crack with water.
Another wave forces more water into the crack.
This pressure causes the crack to get bigger.
Eventually, the rock breaks apart into smaller pieces
that are further eroded by waves.
23.5 The Restless Oceans
Wave Erosion and Deposition
Abrasion also breaks up rocks into smaller
pieces. The sediment carried by waves acts
like sandpaper, rubbing away at the rocks.
Sand is continuously eroded and deposited
along the shore by waves and currents.
23.5 The Restless Oceans
Wave Erosion and Deposition
Longshore drift is the process that moves
sand along a shore.
Currents move large amounts of sediment
parallel to the shore. When these currents
meet a bend in the shoreline, they slow down
and deposit the sediment. This deposit is
called a spit.
23.5 The Restless Oceans
Wave Erosion and Deposition
Longshore drift can carry sediment great
distances along the shore, creating long sandbars
or spits that grow parallel to the shoreline.
Direction of
longshore drift
Movement of
sand grains
23.5 The Restless Oceans
Wave Erosion and Deposition
Deposition by Currents and Waves
The sediment that is eroded from a coastline or
brought to the ocean by rivers is also deposited.
Currents and waves deposit sediment in bays and
inlets as the water slows down.
23.5 The Restless Oceans
Wave Erosion and Deposition
A shoreline covered with sand or other
sediment is a beach.
In many areas, rivers that discharge into the
ocean are the main source of the sand on
ocean beaches.
23.5 The Restless Oceans
Assessment Questions
1. Which of the following increases with depth in the
ocean?
a.
b.
c.
d.
temperature
pressure
light
erosion
23.5 The Restless Oceans
Assessment Questions
1. Which of the following increases with depth in the
ocean?
a.
b.
c.
d.
temperature
pressure
light
erosion
ANS: B
23.5 The Restless Oceans
Assessment Questions
2. What causes surface currents?
a.
b.
c.
d.
convection currents
plate tectonic movement
differences in density
wind
23.5 The Restless Oceans
Assessment Questions
2. What causes surface currents?
a.
b.
c.
d.
convection currents
plate tectonic movement
differences in density
wind
ANS: D
23.5 The Restless Oceans
Assessment Questions
1. Hydraulic action is the process that moves sand
along a shore.
True
False
23.5 The Restless Oceans
Assessment Questions
1. Hydraulic action is the process that moves sand
along a shore.
True
False
ANS:
F, Longshore drift