16.the dynamic ocean

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PrenticeHallEARTH SCIENCE

Tarbuck Lutgens


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Chapter

16The Dynamic Ocean


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Surface Circulation

16.1 The Composition of Seawater

Ocean current is the mass of ocean waterthat flows from one place to another.

Surface Currents

Surface currents are movements of water thatflow horizontally in the upper part of the oceans

surface.

Surface currents develop from friction betweenthe ocean and the wind that blows across itssurface.


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Ocean Surface Currents


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Surface CirculationGyres


Gyres are huge circular-moving current systems

that dominate the surfaces of the oceans. The Coriolis effect is the deflection of currents

away from their original course as a result ofEarths rotation.


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Surface CirculationOcean Currents and Climate


When currents from low-latitude regions move

into higher latitudes, they transfer heat fromwarmer to cooler areas on Earth.

As cold water currents travel toward the equator,they help moderate the warm temperatures of

adjacent land areas.


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False-Colored Satellite Imageof the Gulf Stream


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Surface CirculationUpwelling


Upwelling is the rise of cold water from deeper

layers to replace warmer surface water.

Upwelling brings greater concentrations ofdissolved nutrients, such as nitrates andphosphates, to the ocean surface.


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Effects of Upwelling


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Deep-Ocean CirculationDensity Currents


Densitycurrents are vertical currents of ocean

water that result from density differences amongwater masses.

An increase in seawater density can be causedby a decrease in temperature or an increase in

salinity.


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Deep-Ocean CirculationHigh Latitudes


Most water involved in deep-ocean currents

begins in high latitudes at the surface.

Evaporation

Density currents can also result from increasedsalinity of ocean water due to evaporation.


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Deep-Ocean CirculationA Conveyor Belt


In a simplified model, ocean circulation is similar

to a conveyor belt that travels from the AtlanticOcean, through the Indian and Pacific Oceans,and back again.


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Conveyor Belt Model


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Cross Section of the Arctic Ocean


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WavesWave Characteristics

16.2 Waves and Tides

Most ocean waves obtain their energy and

motion from the wind. The wave height is the vertical distance

between the trough and crest.

The wavelength is the horizontal distance

between two successive crests or twosuccessive troughs.


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WavesWave Characteristics


The wave period is the time it takes one full

waveone wavelengthto pass a fixedposition.

The height, length, and period that areeventually achieved by a wave depend on threefactors: (1) wind speed, (2) length of time thewind has blown, and (3) fetch.

Fetch is the distance that the wind has traveledacross open water.


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Anatomy of a Wave


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WavesWave Motion


Circular orbital motion allows energy to move

forward through the water while the individualwater particles that transmit the wave movearound in a circle.


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WavesBreaking Waves


Changes occur as a wave moves onto shore.

As the waves touch bottom, wave speeddecreases. The decrease in wave speed resultsin a decrease in wavelength and an increase inwave height.


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Breaking Waves


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Tides

Ocean tides result from the gravitationalattraction exerted upon Earth by the moonand, to a lesser extent, by the sun.


Tides are daily changes in the elevation ofthe ocean surface.

Tide-Causing Forces The force that produces tides is gravity.

Tid B l E h


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Tide Bulges on EarthCaused by the Moon


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TidesTide Cycle


Spring tides are tides that have the greatesttidal range due to the alignment of the Earthmoonsun system.

Tidal range is the difference in height between

successive high and low tides.

Neap tides are tides that have the lowest tidalrange, occurring near the times of the first-quarter and third-quarter phases of the moon.


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EarthMoonSun Positionsand the Tides


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TidesTidal Patterns


Three main tidal patterns exist worldwide:

diurnal tides, semidiurnal tides, and mixed tides.


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Forces Acting on the ShorelineA beach is the accumulation of sedimentfound along the shore of a lake or ocean.

16.3 Shoreline Processes and Features

Waves along the shoreline are constantlyeroding, transporting, and depositingsediment. Many types of shoreline featurescan result from this activity.


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Forces Acting on the ShorelineWave Impact


The impact of large, high-energy waves against

the shore can be awesome in its violence. Eachbreaking wave may hurl thousands of tons ofwater against the land, sometimes causing theground to tremble.

Abrasion Abrasion is the sawing and grinding action of

rock fragments in the water.

Abrasion is probably more intense in the surf

zone than in any other environment.


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Forces Acting on the ShorelineWave Refraction


Wave refraction is the bending of waves, and it

plays an important part in the shoreline process. Because of refraction, wave energy is

concentrated against the sides and ends ofheadlands that project into the water, whereas

wave action is weakened in bays.


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Forces Acting on the ShorelineLongshore Transport


A longshore current is a near-shore current that

flows parallel to the shore. Turbulence allows longshore currents to easily

move fine suspended sand and to roll largersand and gravel particles along the bottom.


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Longshore Currents


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Erosional FeaturesShoreline features that originate primarilyfrom the work of erosion are called

erosional features. Sediment that istransported along the shore and depositedin areas where energy is low producesdepositional features.



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Erosional FeaturesWave-Cut Cliffs and Platforms


Wave-cut cliffs result from the cutting action of

the surf against the base of coastal land. A flat,bench-like, wave-cut platform forms in front ofthe wave-cut cliff.

Sea Arches and Sea Stacks

When two caves on opposite sides of aheadland unite, a sea arch results. Eventually,the arch falls in, leaving an isolated remnant, orsea stack, on the wave-cut platform.


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Sea Arch and Sea Stack


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Depositional FeaturesSpits, Bars, and Tombolos


Where longshore currents and other surf zone

currents are active, several features related tothe movement of sediment along the shore maydevelop.

- A spit is an elongated ridge of sand that projectsfrom the land into the mouth of an adjacent bay.

- A baymouth bar is a sandbar that completelycrosses a bay.

- A tombolo is a ridge of sand that connects anisland to the mainland or to another island.


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Evolution of Shoreline Features


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Depositional FeaturesBarrier Islands


Barrier islands are narrow sandbars parallel to,

but separate from, the coast at distances from 3to 30 kilometers offshore.


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Barrier Islands


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Stabilizing the ShoreProtective Structures


Groins, breakwaters, and seawalls are some

structures built to protect a coast from erosion orto prevent the movement of sand along a beach.

Beach Nourishment Beach nourishment is the addition of large

quantities of sand to the beach system.

Miami Beach Before and After


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Miami Beach Before and AfterBeach Nourishment

16.the dynamic ocean

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