23.5 the restless oceans wave action is the primary means of erosion along coastlines

23.5 The Restless Oceans

Wave action is the primary means of erosion along coastlines.


How do conditions in the ocean change with depth?

Exploring the Ocean

Light and temperature decrease with depth, whereas pressure increases.


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).

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.

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.

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.

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.

Exploring the Ocean


What causes surface currents, density currents, and upwelling?

Ocean Currents

Winds blowing across the surface of the ocean cause the continuous flow of surface 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.

Ocean Currents

Deep ocean currents are caused by differences in the density of ocean water.


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.

Ocean Currents


Prevailing wind patterns drive the ocean’s surface currents.

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.

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.

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.

Ocean Currents


Deep Currents

Unlike surface currents, deep currents are not caused by winds.

Denser water results from colder temperatures or higher salinity.

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.

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.

Ocean Currents


Upwelling of deeper ocean water occurs along some coastlines.

Ocean Currents

Surface wind

Warm surface water

Cold water upwelling


How do waves erode rock and deposit sediment?

Wave Erosion and Deposition

Two physical processes, hydraulic action and abrasion, are responsible for much wave erosion.


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.



A. A sea cliff with a sea stack and arch in Etretat, France




B. A barrier beach in South Carolina




B. A barrier beach in South Carolina

C. A sand spit along the Red Sea in Egypt.



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.



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.



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.



Longshore drift can carry sediment great distances along the shore, creating long sandbars or spits that grow parallel to the shoreline.


Movement ofsand grains

Direction of longshore drift


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.



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.



Assessment Questions

1. Which of the following increases with depth in the ocean? a. temperature

b. pressure

c. light

d. erosion



1. Which of the following increases with depth in the ocean? a. temperature

b. pressure

c. light

d. erosion

ANS: B



2. What causes surface currents? a. convection currentsb. plate tectonic movementc. differences in densityd. wind



2. What causes surface currents? a. convection currentsb. plate tectonic movementc. differences in densityd. wind

ANS: D



1. Hydraulic action is the process that moves sand along a shore.

TrueFalse



1. Hydraulic action is the process that moves sand along a shore.

TrueFalse

ANS: F, Longshore drift

23.5 the restless oceans wave action is the primary means of erosion along coastlines

Documents

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