The Oceans & The Oceans & Waves Waves Steve Terrill/Stock Market
Jan 04, 2016
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