The Oceans & The Oceans & WavesWaves

Steve Terrill/Stock Market

I. SEAWATERI. SEAWATER• Covers 71% of Earth’s surfaceCovers 71% of Earth’s surface

• Nature of seawaterNature of seawater

– 35o/oo dissolved salts (30-38)

– Varies from place to place

• Origin of seawaterOrigin of seawater

– Volcanoes?

– Comets?

– Excess H+ & O-?

II.II. CURRENTSCURRENTS

• Ocean water moves constantly - sideways, up, down because it is:– Heated unevenly– Evaporated unevenly– Blown by wind– Affected by Earth’s rotation – Pulled by sun & moon

• Currents are the flow of water between areas of different surface levels or different surface levels or different densitiesdifferent densities

Surface ocean currents arerun by climate & rotation

Density CurrentsDensity Currents• Function of Function of

– Temperature (polar regions)– Salinity (Mediterranean Sea)– Suspended materials (turbidities- flow of

muddy water down a slope)

• Deep ocean currents move byDeep ocean currents move by– density & thermal differences – the Coriolis effect

• NADW, AABWNADW, AABW

Average surface salinity of the oceans

August sea-surface temperatures

Circulation of the Atlantic OceanCirculation of the Atlantic Ocean

CONVEYOR BELT

CONVEYOR BELT

Turbidity Currents

III. TidesIII. Tides

Twice daily rise and fall of the sea caused

by the gravitational attraction between

• earth and moon (lunar tides)

• earth and sun (solar tides)

Function of distance between and mass distance between and mass ofof the Earth, Moon and Sun

Interaction between lunar and solar tides during the lunar month

causes:

• Neap tides: when two tidal components

are out-of-phase, hence lower than

usual, and

• Spring tides: when two tidal components are in-phase, hence higher than usual.

The highest

and lowest tides occur due to the interaction

of earth, moon, and

sun

The effect of tides on a tidal inlet.

Exposed tidal flats

Mont-Saint-MichelFrance

Thierry Prat/Sygma

Terrace Exposed at Low Tide

James Valentine

IV. WAVESIV. WAVES

• Waves are described byWaves are described by – Wave length(L): distance between crests– Wave height (H) : vertical distance

between crest and trough– Wave period (T): time for successive

waves to pass a fixed point– Wave velocity (V) of waves (V = L/T)

• 2 kinds of waves2 kinds of waves– Deep water waves– Shallow water waves

Wind-generated Orbital WavesWind-generated Orbital Waves

Most waves are generated in the open ocean &

• height depends on:

– Wind velocity

– Wind duration

– Distance over which wind blows called

the FETCH, usually a big storm.

Shallow water wavesShallow water waves

• At water depth of L/2, wave feels bottom. Then:

• Wave height Increases as

• Wave length decreases.

• Velocity decreases because wave is dragging on bottom.

• Period doesn’t change

• When wave reaches 1.3H -> BREAKER

Wave refractionWave refraction

• Bending of wave crests as they approach the

beach at an angle

• Caused by the change in velocity of waves as

a function of water depth

• Only a small part of each wave feels bottom

at a time so only a small part of wave slows.

Wave Refraction

Waves Bending as they Approach the Beach

John S. Shelton

Sediment transport near Sediment transport near shore, parallel to the beachshore, parallel to the beach

• Longshore driftLongshore drift: sediment carried by swash and backwash along the beach

• Longshore currentsLongshore currents: currents parallel to the beach within the surf zone

Longshore Drift

V. COASTSV. COASTS

• BEACHES

• EROSIONAL COASTS -uplift

• DEPOSITIONAL COASTS - sinking

• CHANGES IN SEA LEVEL-relative

Refraction at Headlands and BaysRefraction at Headlands and Bays

Carving a coastCarving a coast

• Waves & currents act the same as streams except work in both directions

• Erode - in high energy areas by– Abrasion– Solution– Wave pressure

• Deposit -in low energy areas

Sandy Beach, North Carolina Barrier Island

Peter Kresan

Boulder Beach, Massachusetts

Raymond Siever

Major parts of beachesMajor parts of beaches

• OffshoreOffshore: from where the waves begin

to feel bottom to the surf zone

• ForeshoreForeshore: includes the surf zone, tidal

flats, and swash zone

• BackshoreBackshore: from beyond the swash zone to the highest level of the beach

Major Parts of a BeachMajor Parts of a Beach

Sand Budget of a Beach

Factors determining rates of Factors determining rates of erosion or depositionerosion or deposition

• Uplift

• Subsidence

• Rock type

• Sea-level changes

• Storm wave heights

• Tidal range

Erosional CoastsErosional Coasts

• Region of up-lift - JOB IS TO STRAIGHTEN SHORELINE

• Prominent cliffs & headlands

• Narrow inlets, irregular bays & beaches

• Undercut cliffs

– Sea stacks

– Wave-cut terraces

• Falling sea level

Sea Stacks

Kevin Schafer

Wave-cut TerraceExposed at Low Tide

John S. Shelton

Uplifted Coastal Terrace

John S. Shelton

Depositional CoastsDepositional Coasts

• Sinking coasts

• Long, wide beaches– Bars– Spits– Barrier islands– Tidal flats & shallow lagoons

• Low-lying, sedimentary coastal plains

• Rising sea level - estuary

Southern Tip of Cape Cod

Steve Durwell/The Image Bank

Partially Developed Barrier Island

Gulf of Mexico

LagoonMainland Florida

Barrier Island

Richard A. Davis, Jr

Effects of rising sea level:Effects of rising sea level:Eastern North America and EuropeEastern North America and Europe

VI. Preventing beach erosionVI. Preventing beach erosion

• StructuralStructural approaches (e.g.,

groins): typically cause increased

erosion down current of structure

• Non-structuralNon-structural approaches (e.g., beach nourishment, land use planning): expensive, but don’t cause erosion in new areas

Groin: Built to Prevent Updrift Erosion Causes

Downdrift Erosion

Deposition

Erosion

Phillip Plissin/Explorer

Interrupting Interrupting longshore longshore currentscurrents

Beach Nourishment, New Jersey

U.S. Corps of Engineers, New York District

From volcanic island to an atoll From volcanic island to an atoll

Some of the Maldive

Islands in the Pacific

Atoll

Fringing Reef

Guido Alberto Rosi/The Image Bank

IX. Types of marine sedimentIX. Types of marine sediment

• TerrigenousTerrigenous material eroded from the continents

• BiochemicallyBiochemically precipitated

shells of marine organisms

• AbioticAbiotic chemical precipitates

• ExtraterrestrialExtraterrestrial material

Oceanic Ooze

Scripps Institute of Oceanography,University of California, San Diego

The END

Carbonate Compensation DepthDepth below which carbonate material

dissolves in seawater

Origin of the lunar

tides

Changes in Waves as they Approach the Beach