Chapter 16 The dynamic ocean.ppt - Mrs. Kaser's Science … 16 The dyna… · Surface Circulation...

Chapter

The Dynamic Ocean

An ocean current is the mass ofocean water that flows from oneplace to another.

Surface Circulation

16.1 The Composition of Seawater

Surface Currents

• Surface currents are movements• Surface currents are movementsof water that flow horizontally in theupper part of the ocean’s surface.

• Surface currents develop fromfriction between the ocean and thewind that blows across its surface.

Ocean Surface Currents

Gyres


• Gyres are huge circular-movingcurrent systems that dominate thesurfaces of the oceans.

Surface Circulation

surfaces of the oceans.

• The Coriolis effect is the deflectionof currents away from their originalcourse as a result of Earth’srotation.

Ocean Currents and Climate


• When currents from low-latituderegions move into higher latitudes,they transfer heat from warmer to

Surface Circulation

they transfer heat from warmer tocooler areas on Earth.

• As cold water currents traveltoward the equator, they helpmoderate the warm temperatures ofadjacent land areas.

False-Colored Satellite Imageof the Gulf Stream

Upwelling


• Upwelling is the rise of cold waterfrom deeper layers to replacewarmer surface water.

Surface Circulation

warmer surface water.

• Upwelling brings greaterconcentrations of dissolvednutrients, such as nitrates andphosphates, to the ocean surface.

Effects ofUpwelling

Density Currents


• Density currents are verticalcurrents of ocean water that resultfrom density differences among

Deep-Ocean Circulation

from density differences amongwater masses.

• An increase in seawater densitycan be caused by a decrease intemperature or an increase insalinity.

High Latitudes


• Most water involved in deep-oceancurrents begins in high latitudes atthe surface.


the surface.

Evaporation

• Density currents can also resultfrom increased salinity of oceanwater due to evaporation.

A Conveyor Belt


• In a simplified model, oceancirculation is similar to a conveyorbelt that travels from the Atlantic


belt that travels from the AtlanticOcean, through the Indian andPacific Oceans, and back again.

Conveyor Belt Model

Cross Section of the Arctic Ocean

Wave Characteristics

16.2 Waves and Tides

• Most ocean waves obtain theirenergy and motion from the wind.

• The wave height is the vertical• The wave height is the verticaldistance between the trough andcrest.

• The wavelength is the horizontaldistance between two successivecrests or two successive troughs.

Anatomy of a Wave



• The height, length, and period thatare eventually achieved by a wavedepend on three factors: (1) winddepend on three factors: (1) windspeed, (2) length of time the windhas blown, and (3) fetch.



• The wave period is the time ittakes one full wave—onewavelength—to pass a fixedwavelength—to pass a fixedposition.

• Fetch is the distance that the windhas traveled across open water.

Waves

Wave Motion


• Circular orbital motion allows• Circular orbital motion allowsenergy to move forward throughthe water while the individualwater particles that transmit thewave move around in a circle.

Waves Breaking Waves


• Changes occur as a wave movesonto shore.onto shore.

• As the waves touch bottom, wavespeed decreases. The decrease inwave speed results in a decrease inwavelength and an increase inwave height.

Breaking Waves

Ocean tides result from thegravitational attraction exerted


Tides are daily changes in theelevation of the ocean surface.

gravitational attraction exertedupon Earth by the moon and, to alesser extent, by the sun.

Tide-Causing Forces• The force that produces tides is

gravity.

Tide Bulges on EarthCaused by the Moon

Tide Cycle


• Tidal range is the difference inheight between successive highheight between successive highand low tides.

Tide Cycle


• Spring tides are tides that have thegreatest tidal range due to thealignment of the Earth–moon–sunalignment of the Earth–moon–sunsystem.

• Neap tides are tides that have thelowest tidal range, occurring nearthe times of the first-quarter andthird-quarter phases of the moon.

Earth–Moon–Sun Positionsand the Tides

Earth–Moon–SunPositions

and the Tides

Tidal Patterns


• Three main tidal patterns exist• Three main tidal patterns existworldwide: diurnal tides,semidiurnal tides, and mixedtides.

Forces Acting on the Shoreline A beach is the accumulation of

sediment found along the shore ofa lake or ocean.

16.3 Shoreline Processes and Features

a lake or ocean.

Waves along the shoreline areconstantly eroding, transporting,and depositing sediment. Manytypes of shoreline features canresult from this activity.

Forces Acting on the ShorelineWave Impact


• The impact of large, high-energywaves against the shore can be

• The impact of large, high-energywaves against the shore can beawesome in its violence. Eachbreaking wave may hurl thousandsof tons of water against the land,sometimes causing the ground totremble.

Forces Acting on the Shoreline


Abrasion

• Abrasion is the sawing and• Abrasion is the sawing andgrinding action of rock fragmentsin the water.

• Abrasion is probably more intensein the surf zone than in any otherenvironment.

Wave Refraction


• Wave refraction is the bending ofwaves, and it plays an importantpart in the shoreline process.


part in the shoreline process.

• Because of refraction, waveenergy is concentrated againstthe sides and ends of headlandsthat project into the water,whereas wave action is weakenedin bays.

Wave Refraction

Longshore Transport


• A longshore current is a near-shore current that flows parallel tothe shore.


the shore.

• Turbulence allows longshorecurrents to easily move finesuspended sand and to roll largersand and gravel particles along thebottom.

Longshore Currents

Erosional Features

Shoreline features that originateprimarily from the work of erosion


primarily from the work of erosionare called erosional features.Sediment that is transported alongthe shore and deposited in areaswhere energy is low producesdepositional features.

Erosional Features

Wave-Cut Cliffs and Platforms


• Wave-cut cliffs result from the• Wave-cut cliffs result from thecutting action of the surf againstthe base of coastal land. A flat,bench-like, wave-cut platformforms in front of the wave-cut cliff.

Erosional Features


Sea Arches and Sea Stacks

• When two caves on opposite sides• When two caves on opposite sidesof a headland unite, a sea archresults. Eventually, the arch falls in,leaving an isolated remnant, or seastack, on the wave-cut platform.

Sea Arch and Sea Stack

Depositional Features

Spits, Bars, and Tombolos


• Where longshore currents and• Where longshore currents andother surf zone currents are active,several features related to themovement of sediment along theshore may develop.

Spits, Bars, and Tombolos


- A spit is an elongated ridge ofsand that projects from the landinto the mouth of an adjacent bay.


into the mouth of an adjacent bay.

- A baymouth bar is a sandbar thatcompletely crosses a bay.

- A tombolo is a ridge of sand thatconnects an island to the mainlandor to another island.

Evolution ofShorelineFeaturesFeatures


Barrier Islands


• Barrier islands are narrow• Barrier islands are narrowsandbars parallel to, but separatefrom, the coast at distances from 3to 30 kilometers offshore.

Barrier Islands

Stabilizing the Shore Protective Structures


• Groins, breakwaters, and seawallsare some structures built to protectare some structures built to protecta coast from erosion or to preventthe movement of sand along abeach.


Beach Nourishment• Beach nourishment is the addition

of large quantities of sand to thebeach system.

Stabilizing the Shore

Miami Beach Before

andand

AfterBeach Nourishment

Chapter 16 The dynamic ocean.ppt - Mrs. Kaser's Science … 16 The dyna… · Surface Circulation...

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