6. Oceanography
• Seismic reflection profiling.
• Sound waves
• Some waves
• Travel time of
• Used to make images of
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7. Outline
• Ocean exploration & oceanography
• The globes’ oceans
-Lithosphere density and ocean basins
-Global ocean landscape
• Submarine landscape
-Major zones (shelf to Abyssal plains) – reflection of tectonics
-Continental margins, submarine canyons
-Ocean water composition, temperature
• Ocean dynamics
-Currents, Coriolis effect, tides, waves
• Coastal landforms
-beaches, barrier islands, rocky coasts, tidal flats, reefs etc..
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8. The Global Oceans
• Ocean covers
• Largest reservoir
• Oceans…
• Serve as
• Regulate
• Cycle
• Linked to
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9. Global Landscape
• Oceans exist because of lithosphere differences.
• Continental lithosphere floats higher
• Oceanic lithosphere
• Ocean basins collect
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10. Global Ocean Landscape
• The world ocean is divided into smaller oceans
• Tectonic processes constantly change the map
• Biotic activity: oceans (chlorophyll content) and land
(vegetation)
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11. Global Ocean Landscape
• Present configuration of tectonic plates…
• Most continental crust in northern hemisphere
• Most oceanic crust in southern hemisphere
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12. Outline
• Ocean exploration & oceanography
• The globes’ oceans
-Lithosphere density and ocean basins
-Global ocean landscape
• Submarine landscape
-Major zones (shelf to Abyssal plains) – reflection of tectonics
-Continental margins, submarine canyons
-Ocean water composition, temperature
• Ocean dynamics
-Currents, Coriolis effect, tides, waves
• Coastal landforms
-beaches, barrier islands, rocky coasts, tidal flats, reefs etc..
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15. Undersea Landscapes
Continental margins:
• Passive (broad shelf, no plate boundary)
• Active (narrow shelf, trench, accr. prism, plate boundary)
Western SA: active
Eastern NA: passive
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16. Undersea Landscapes
• Submarine canyons cut continental shelves.
• Associated with large rivers
• Carved during sea level lowstands
• Funnel sediments to deeper water
• Submarine fans grow where canyons empty onto the Ab plain
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17. Ocean Water Composition
• Normal marine salinity, reflecting dissolved ions, is 3.5%
• (35g/L; 35000 parts/million)
• Dissolved ions derive from rock chemical weathering
• Ions mostly Cl(neg.), Na(pos.), SO42-, Ca2+,
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18. Ocean Water Composition
• Surface salinity can vary.
• Higher salinity evaporation and sea-ice form
• Lower salinity rainfall, glacial melt, river input
• Salinity becomes more uniform with depth.
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19. Ocean Water Temperature
• Ocean surface T varies inversely with latitude.
• Water buffers wide T shifts (moderates climate)
• Water T approaches a uniform value with depth
• Ocean bottom water is near freezing <4 degrees C (39F)
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20. Outline
• Ocean exploration & oceanography
• The globes’ oceans
-Lithosphere density and ocean basins
-Global ocean landscape
• Submarine landscape
-Major zones (shelf to Abyssal plains) – reflection of tectonics
-Continental margins, submarine canyons
-Ocean water composition, temperature
• Ocean dynamics
-Currents, Coriolis effect, tides, waves
• Coastal landforms
-beaches, barrier islands, rocky coasts, tidal flats, reefs etc..
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21. Oceanic Currents
• Currents continuously move ocean water in 3D
• Surface currents (upper 100 m) - due to wind shear
• Current motion creates large spirals (notice a pattern?)
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22. The Coriolis Effect
• Earth rotation deflects prevailing winds and currents.
• Acts as an “apparent” force on winds/currents
• Coriolis deflection sense depends upon…
• Direction of motion
• Position relative to equation
Merry-go-round analogy:
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23. The Coriolis Effect
• Surface winds & currents are both influenced
• North hemisphere:
• S-moving winds/currents deflected W
• N-moving winds/currents deflected E
• South hemisphere.
• N-moving winds/currents deflected W
• S-moving winds/currents deflected E
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24. Vertical Oceanic Currents
• Currents also transport ocean water vertically
• Downwelling – surface waters drawn downward
• Upwelling – deep waters pushed upward
• Wind perpendicular to shore drives vertical flow
• Onshore – water piling up along coast drives downwelling
• Offshore – upwelling replaces water moved away
Downwelling Upwelling
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25. Vertical Oceanic Currents
• Thermohaline contrast also drives vertical currents
• Temp – cold water is dense -> sinks
• Salinity – More saline water is dense -> sinks
• Polar water is both colder and saltier
• Deep ocean waters are replenished from poles
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26. Oceanic Currents
• Sinking polar water is replaced by surface flow
• This process carries warm water up from tropics
• These surface currents warm northern oceans
• System forms a a global “conveyor belt”
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27. Tides
• Sea level rises and falls twice daily
• High tide – maximum tidal flooding
• Low tide – maximum tidal withdrawal
• Tidal reach – range between high and low tides
• Intertidal zone lies between tides
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28. Tides
• Caused by:
• Gravitational pull of moon and sun
• Centrifugal forces from Earth, Moon, and Sun rotations
• Orbiting moon creates strongest tidal effects.
• Sublunar bulge follows Moons orbit
• Smaller bulge occurs on opposite side of Earth
• Bulges = high tides ; low tides = between bulges
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30. Waves
• Ocean waves develop via friction from wind on water.
• Gentle wind small waves ; gales giant waves
• Waves move upper part of the water
• Wave height, length, and period depend on wind speed,
wind duration, and travel distance (fetch).
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31. Waves
• Wave anatomy:
• Crest – wave top
• Trough – low between crusts
• Wavelength – distance b/w adjacent wave crests
• Depth of influence (wave base) is ½ the wavelength.
• Above wave base, water moves in circular motion
• Below wave base, water is not affected
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32. Waves
• As waves approach shore, wave base hits bottom
• Friction slows wave motion near sea floor
• Near surface, waves continue moving fast
• Wave over-steepens and crests
• This zone features diverse environments.
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33. Waves
• Waves that crash onto beach breakers
• Wave energy dissipated by turbulence
• Creates white water in surf zone
• Water surge (swash) rushes up beach face
• Gravity pulls backwash back down beach slope.
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34. Wave Refraction
• Irregular shoreline water depth varies
• As waves drag on bottom, they are forced to bend.
• This process, wave refraction, has consequences:
• Wave attack concentrated on headlands
• Wave attack is dissipated in embayments
• Tend to straighten irregular shores.
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35. Longshore Currents
• Sediment is transported along shore.
• Oblique waves push sediment sideways up the beach
• Gravity then pulls this sediment straight downslope.
• Zig-zag pattern moves sediment in one direction
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36. Rip Currents
• Develop when wave flow is perpendicular to shoreline
• Water piles up on beach, must return seaward
• Rip current develops perpendicular to beach
• Rip currents are often strong; people can get pulled under.
• Rip currents dissipate away from the surf zone
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37. Outline
• Ocean exploration & oceanography
• The globes’ oceans
-Lithosphere density and ocean basins
-Global ocean landscape
• Submarine landscape
-Major zones (shelf to Abyssal plains) – reflection of tectonics
-Continental margins, submarine canyons
-Ocean water composition, temperature
• Ocean dynamics
-Currents, Coriolis effect, tides, waves
• Coastal landforms
-beaches, barrier islands, rocky coasts, tidal flats, reefs etc..
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42. Beaches
• Distinct zones exist along a beach profile.
• Foreshore or intertidal – region between high and low tide
• Beach face – steep, concave zone formed by wave smash
• Backshore – upper part of beach
• Beyond reach of normal high tides
• Often exhibit berms (stepped terraces of storm sediment)
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43. Beaches
• Longshore currents move sediments along beaches
• This process, beach drift, moves tons of sand daily
• Beach drift builds bars and spits
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44. Beach Drift
Beach Drift
This animation illustrates the sawtooth motion that causes
sand to gradually migrate along beaches in a process called
beach drift, and shows how this can create sand spits in
places where the coastline indents landward. For more
information, see Section 18.6 Where Land Meets Sea:
Coastal Landforms starting on p. 638 and Figure 18.20 in
your textbook.
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45. Barrier Islands
• Barrier islands are elongate, linear sand bars.
• Form where sand is plentiful
• Protected backwater area called a lagoon
• Common places for development
• They are ephemeral (temporary!)
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46. Tidal Flats
• Form in intertidal zones lacking strong waves
• Common behind barrier islands or in estuaries
• Thinly laminated sand and muds
• Ancient tidal flat sediments well-studied – past sea level
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47. Rocky Coasts
• Bedrock intersects the sea
• Wave action
• Wave energy acts
• Develop unique
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48. Rocky Coasts
• Wave-cut notches – waves erode an oberhang
• Cliff collapses and process resumes
• Over time, cliff retreat is marked by a wave-cut bench
• An erosional remnant of of former cliffs
• Often exposed at low tide
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49. Rocky Coasts
• Rocky headlands are preferentially eroded.
• Refracted waves focus energy to headland sides.
• Erosion from both sides creates a sea arch.
• Collapse of the sea arch leaves remnant sea stacks.
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50. Wetlands
• Wetlands cover large coastal regions.
• Develop in places protected from waves and currents.
• Fuel high biological productivities
• Vegetation governed by climate
• Temperate – vegetated by trees, grasses, or mosses
• Tropical – mangroves dominate
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51. Estuaries
• River valleys flooded by marine water
• Mixed fresh and salt water
• Modern estuaries are relation to glaciation
• Rivers carved canyons during sea-level lows
• Sea-level rise flooded the canyons
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52. Fjords
• Flooded U-shaped valleys carved by glaciers
• Form spectacular
• Notable examples found in…
• Norway.
• British Columbia.
• New Zealand.
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53. Reefs
• Coral reefs grow in tropical marine settings
• Large structures of cemented skeletons.
• Most biologically productive ecosystems.
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54. Reefs
• Coral reefs modify sediment accumulations
• Reefs alter wave and current energy
• Protect leeward environments.
• Abundant debris is shed to adjacent environments.
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55. Reefs
• Coral atolls reefs formed on subsiding volcano
• Reef is established when volcano is active
• After extinction, volcano erodes and subsides
• Reef can easily keep pace with subsidence
• Reef continues long after volcano is below sea level
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57. Coastal Variability
• Global sea-level changes effect coasts worldwide.
• Inflation/deflation of mid-ocean ridges
• Glaciation/deglaciation traps or releases water
• Pleistocene glaciations exposed all continental shelfs
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58. Coastal Variability
• Emergent coasts experience relative sea-level fall.
• Via uplift due to tectonic processes.
• Via sea-level drop (due to global climate change)
• Emergent coasts characterized by…
• River incision, cliffs, wave-cut notches
• Terraces representing former sea-level positions
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59. Coastal Variability
• Submergent coasts experience relative sea-level rise
• Subsidence of passive margin (i.e., deltaic sediments)
• Global sea-level rise
• characterized by river or glacial valleys that create
estuaries and fjords.
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60. Coastal Variability
• Shoreline character is linked to
• Balance between
• Accretionary coasts –
• Erosional coasts –
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61. Coastal Variability
• Climate is a strong influence on
• Harsh weather enhances
• Calm weather favors
• Tropics –
• Temperate –
• Arctic –
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62. Coastal Problems
• Sea-level change.
• Sea level is
• Rate of
• People living in
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63. Coastal Problems
• Beach
• Storms (e.g. hurricanes)
• Human development in coastal settings
• Construction in coastal settings is
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64. Mitigating Coastal Problems
• Artificial barriers built to
• Groins, jetties, breakwaters
• Usually produces
• Deposition is enhanced
• BUT, erosion is accelerated
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65. Mitigating Coastal Problems
• Approach to combat erosion
• Seawalls may hasten erosion.
• Wave energy is
• Erosion enhanced
• Seawalls can
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