16. Undersea Landscapes
• Submarine canyons
• Associated with
• Carved during
• Funnel sediments to
• Submarine fans grow where
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17. Ocean Water Composition
• Normal marine salinity, reflecting dissolved ions, is
• 3.5%
• Dissolved ions derive from rock chemical weathering
• Ions mostly cl, Na, SO, Mg, Ca, K
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18. Ocean Water Composition
• Surface salinity can vary.
• Higher salinity evaporation and sea ice formation
• 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 degree C
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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 equator
• 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 to W
• N-moving winds/currents deflected to E
• South hemisphere.
• N-moving winds/currents deflected to W
• S-moving winds/currents deflected to 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
• 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 cold and salty
• Deep ocean waters are replenished from poles
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26. Oceanic Currents
• Sinking polar water is replaced by surface flows
• This process carries warm water up from the tropics
• These surface currents warm northern oceans
• System forms a global “conveyor belt”
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27. Tides
• Sea level rises and falls twice daily
• High tide – max tidal flooding
• Low tide – max 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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29. Tides
• Lunar & solar tidal effects interact
• Positive alignment yields enhance spring tides
• Negative alignment results in dampened neap tides
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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 crests
• Wavelength – distance between adajcent wave crest
• 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
• This zone features
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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 downshore
• 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..
Chapter 18
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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 swash
• Backshore – upper part
• Beyond reach of
• Often exhibit
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43. Beaches
• Longshore currents move sediment 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
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47. Rocky Coasts
• Bedrock intersects
• Wave action is
• Wave energy acts
• Develop unique
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48. Rocky Coasts
• Wave-cut notches – waves erode an overhang
• Cliff collapses and process resumes
• Over time, cliff retreat is marked by a wave cut bench
• An erosional remnant 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
• Erosion from both sides
• Collapse of the
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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 -
• Tropical –
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51. Estuaries
• River valleys flooded by marine water
• Mixed fresh and salt water
• Modern estuaries are related 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 bedrock bounded troughs
• 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 accumulation
• Reefs alter wave and current energy
• Protect
• Abundant debris is shed to adjacent environments.
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55. Reefs
• Coral atolls reefs formed on sudsiding volcano
• Reef is established when 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 shelves
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58. Coastal Variability
• Emergent coasts experience relative sea-level fall
• Via uplift due to tectonic processes
• Via sea-level drop (drop 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 (deltaic sediment)
• Global sea-level rise
• Submergent coasts characterized by flooded river or
glacial valley 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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