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Chapter 18Chapter 18
Oceans and Coasts
Chapter 18
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
Chapter 18Chapter 18
Oceans• Humans have explored the ocean for centuries.• Before 1800s, sea floors was unknown
• HMS Challenger (1872-1876) 1st oceanography study• Dredged sea floor rocks• Measured seawater, depth, currents• Analyzed water• Collected biota
Chapter 18
Chapter 18Chapter 18
Oceans• Our knowledge of oceans has expanded greatly:
• Oceanography – study of ocean water and its movement• Marine geology – study of ocean floor rocks/seds• Marine biology – study of ocean life
Chapter 18
Chapter 18Chapter 18
Oceanography• Instruments have greatly expanded our knowledge.
• Submarine exploration – Alvin (WHOI)• Bathymetric mapping – sonar/radar• Ocean drilling- recovers time archived below the seafloor
• Major drilling projects (DSDP, ODP, IODP)
Chapter 18
Chapter 18Chapter 18
Oceanography• Seismic reflection profiling.
• Sound waves pass through water and sediment• Some waves bounce off each subsurface layer• Travel time of reflected waves captured by geophones• Used to make images of ocean floor geology
Chapter 18
Chapter 18
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
Chapter 18Chapter 18
The Global Oceans• Ocean covers 70.8% of Earth’s surface
• Largest reservoir in hydrologic cycle
• Oceans…• Serve as basis for life• Regulate climate• Cycle mass and energy
• Linked to atmosphere,• lithosphere, biosphere
Chapter 18
Chapter 18Chapter 18
Global Landscape
• Oceans exist because of lithosphere differences. • Continental lithosphere• Oceanic lithosphere
• Ocean basins collect
Chapter 18
Chapter 18Chapter 18
Global Ocean Landscape • The world ocean is
• Tectonic processes
• Biotic activity:
Chapter 18
Chapter 18Chapter 18
Global Ocean Landscape• Present configuration of tectonic plates…
• Most continental crust in• Most oceanic crust in
Chapter 18
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
Chapter 18Chapter 18
Undersea Landscapes• Sea floor bathymetry
• Continental shelf – • Continental slope – • Abyssal plain –
Chapter 18
Chapter 18Chapter 18
Undersea Landscapes• Sea floor reflects
• Continental shelf – • Continental slope – • Abyssal plain –
Chapter 18
Chapter 18Chapter 18
Undersea LandscapesContinental margins:• Passive• Active
Chapter 18
Eastern NA: passive
western SA: active
Chapter 18Chapter 18
Undersea Landscapes
• Submarine canyons• Associated with• Carved during• Funnel sediments to• Submarine fans grow where
Chapter 18
Chapter 18Chapter 18
Ocean Water Composition• Normal marine salinity, reflecting dissolved ions, is
• Dissolved ions derive from• Ions mostly
Chapter 18
Chapter 18Chapter 18
Ocean Water Composition• Surface salinity can vary.
• Higher salinity • Lower salinity
• Salinity becomes
Chapter 18
Chapter 18Chapter 18
Ocean Water Temperature
• Ocean surface T varies• Water buffers• Water T approaches• Ocean bottom water is
Chapter 18
Chapter 18
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
Chapter 18Chapter 18
Oceanic Currents• Currents continuously
• Surface currents (upper 100 m) - due to• Current motion creates
Chapter 18
Chapter 18Chapter 18
The Coriolis Effect• Earth rotation deflects• Acts as an• Coriolis deflection sense depends upon…
• Merry-go-round analogy:
Chapter 18
Chapter 18Chapter 18
The Coriolis Effect• Surface winds & currents are
• North hemisphere:• S-moving winds/currents deflected• N-moving winds/currents deflected
• South hemisphere.• N-moving winds/currents deflected• S-moving winds/currents deflected
Chapter 18
Chapter 18Chapter 18
Downwelling Upwelling
Vertical Oceanic Currents• Currents also transport
• Downwelling – • Upwelling –
• Wind perpendicular to shore• Onshore – • Offshore –
Chapter 18
Chapter 18Chapter 18
Vertical Oceanic Currents• Thermohaline contrast also
• Temp – cold water• Salinity – More saline water
• Polar water is both• Deep ocean waters are
Chapter 18
Chapter 18Chapter 18
Oceanic Currents
• Sinking polar water is• This process carries• These surface currents
• System forms a
Chapter 18
Chapter 18Chapter 18
Tides• Sea level rises and falls
• High tide – • Low tide – • Tidal reach – • Intertidal zone
Chapter 18
Chapter 18Chapter 18
Tides• Caused by:
• Gravitational pull of• Centrifugal forces from
• Orbiting moon creates strongest tidal effects.• Sublunar bulge follows• Smaller bulge occurs• Bulges = ; low tides =
Chapter 18
Chapter 18Chapter 18
Tides
• Lunar & solar tidal effects• Positive alignment yields• Negative alignment results in
Chapter 18
Chapter 18Chapter 18
Waves• Ocean waves develop via friction from wind on water.
• Gentle wind ; gales
• Waves move upper part• Wave height, length, and period depend on
Chapter 18
Chapter 18Chapter 18
Waves• Wave anatomy:
• Crest – • Trough – • Wavelength –
• Depth of influence (wave base) is ½ the wavelength. • Above wave base, water• Below wave base, water
Chapter 18
Chapter 18Chapter 18
Waves• As waves approach shore,
• Friction• Near surface, waves• Wave
• This zone features
Chapter 18
Chapter 18Chapter 18
Waves• Waves that crash onto beach • Wave energy dissipated by
• Creates• Water surge (swash)• Gravity pulls
Chapter 18
Chapter 18Chapter 18
Wave Refraction• Irregular shoreline • As waves drag on bottom, • This process, wave refraction, has consequences:
• Wave attack concentrated• Wave attack is dissipated• Tend to
Chapter 18
Chapter 18Chapter 18
Longshore Currents
• Sediment is transported along shore. • Oblique waves push• Gravity then pulls• Zig-zag pattern
Chapter 18
Chapter 18Chapter 18
Rip Currents• Develop when wave flow is
• Water piles up on beach, • Rip current develops• Rip currents are
• Rip currents dissipate away from
Chapter 18
Chapter 18
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
Chapter 18Chapter 18
Coastal Landforms• A variety of landforms
Chapter 18
Chapter 18Chapter 18
Beaches• Dominated by• Gravel beaches reflect• Muds
• Turbulent surf• Muds transported to
Chapter 18
Chapter 18Chapter 18
Beaches
• Beach sediment composition reflects• Quartz• Carbonates• Resistant
Chapter 18
Chapter 18Chapter 18
Beaches• Beaches develop distinctive• Profiles change
• Summer – • Winter –
Chapter 18
Chapter 18Chapter 18
Beaches• Distinct zones exist along a beach profile.
• Foreshore or intertidal – • Beach face – • Backshore –
• Beyond reach of• Often exhibit
Chapter 18
Chapter 18Chapter 18
Beaches
• Longshore currents move• This process, beach• Beach drift builds
Chapter 18
Chapter 18Chapter 18
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.
Beach Drift
Chapter 18Chapter 18
• Barrier islands are• Form where• Protected backwater area called• Common places for• They are
Barrier Islands
Chapter 18
Chapter 18Chapter 18
• Form in intertidal zones• Common behind• Thinly laminated• Ancient tidal flat sediments
Tidal Flats
Chapter 18
Chapter 18Chapter 18
• Bedrock intersects• Wave action is• Wave energy acts• Develop unique
Rocky Coasts
Chapter 18
Chapter 18Chapter 18
• Wave-cut notches – • Cliff• Over time, cliff
• An erosional remnant of• Often exposed at
Rocky Coasts
Chapter 18
Chapter 18Chapter 18
• Rocky headlands are• Refracted waves focus• Erosion from both sides• Collapse of the
Rocky Coasts
Chapter 18
Chapter 18Chapter 18
• Wetlands cover• Develop in places protected from• Fuel high• Vegetation governed by
• Temperate -• Tropical –
Wetlands
Chapter 18
Chapter 18Chapter 18
• River valleys flooded by• Mixed• Modern estuaries are
• Rivers carved canyons during• Sea-level rise
Estuaries
Chapter 18
Chapter 18Chapter 18
• Flooded• Form spectacular• Notable examples found in…
• Norway.• British Columbia.• New Zealand.
Fjords
Chapter 18
Chapter 18Chapter 18
• Coral reefs grow in• Large structures of• Most biologically productive
Reefs
Chapter 18
Chapter 18Chapter 18
• Coral reefs• Reefs alter• Protect• Abundant debris is shed to adjacent environments.
Reefs
Chapter 18
Chapter 18Chapter 18
• Coral atolls reefs formed on• Reef is established when• After extinction, • Reef can easily keep pace• Reef continues long after
Reefs
Chapter 18
Chapter 18Chapter 18
Coastal Variability
• Plate tectonic setting governs• Passive margin – • Active margin –
Chapter 18
Chapter 18Chapter 18
Coastal Variability• Global sea-level changes effect
• Inflation/deflation of• Glaciation/deglaciation
• Pleistocene glaciations
Chapter 18
Chapter 18Chapter 18
Coastal Variability• Emergent coasts experience relative sea-level
• Via uplift due to• Via sea-level
• Emergent coasts characterized by…• River• Terraces representing
Chapter 18
Chapter 18Chapter 18
Coastal Variability
• Submergent coasts experience relative sea-level• Subsidence of• Global sea-level
• Submergent coasts characterized by
Chapter 18
Chapter 18Chapter 18
Coastal Variability
• Shoreline character is linked to• Balance between
• Accretionary coasts – • Erosional coasts –
Chapter 18
Chapter 18Chapter 18
Coastal Variability• Climate is a strong influence on
• Harsh weather enhances• Calm weather favors• Tropics – • Temperate – • Arctic –
Chapter 18
Chapter 18Chapter 18
Coastal Problems
• Sea-level change.• Sea level is• Rate of
• People living in
Chapter 18
Chapter 18Chapter 18
Coastal Problems
• Beach• Storms (e.g. hurricanes)• Human development in coastal settings• Construction in coastal settings is
Chapter 18
Chapter 18Chapter 18
Mitigating Coastal Problems• Artificial barriers built to
• Groins, jetties, breakwaters• Usually produces
• Deposition is enhanced• BUT, erosion is accelerated
Chapter 18
Chapter 18Chapter 18
• Approach to combat erosion
• Seawalls may hasten erosion.• Wave energy is• Erosion enhanced• Seawalls can
Chapter 18
Mitigating Coastal Problems