The Ocean Floor

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The Ocean Floor

• Chapter 23

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23.1 Studying the Ocean Floor

• Original method sinker on a line
• In deep ocean water a single reading could take
  an entire day
• Echo Sounding
• Sound waves are sent out and bounced back to the
  ship (echo)
• The time it takes for the waves to return is
  recorded and that allows the depth to be
  determined
• These sound waves are sent out continuously to
  prepare a contour diagram of the floor
• The loudness of the echo also tells what type
  of material is on the floor
• sludgesoft echo
• Rockloud echo

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23.1 Studying the Ocean Floor

• Sediment Sampling
• The layers of sediment at the bottom of an ocean
  can tell us much about the earths history
• Examples-
• Core sampling- taking a cross-section of the
  sediments
• Gravity corer
• Piston corer-
• Dredging taking a scoop of sediments
• The cross-section is lost but you do get a larger
  sample of sediments
• Satellite observations
• Echo sounding is slow and tedious
• A satellite reading cannot penetrate through
  water
• A satellite can record minute changes in water
  level that occur because of ocean floor features
• Satellites are the basic tool that map the entire
  floor
• See next slide and p. 512-513

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23.1 Studying the Ocean Floor
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23.2 The Continental Margin

• Parts of the Continental Margin (the part of the
  ocean right next to shore)
• Continental Shelf
• Very flat
• Varying widths (non-existent to 1280 km out)
• Continental Slope
• Starts at the edge of the shelf
• Water depth increases rapidly
• 20 km wide and extends to a depth of 3.6 km
• Like a movie theater aisle
• Sediments tumble off of the slope to the rise

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23.2 The Continental Margin

• Continental Rise
• Starts at the edge of the slope
• Very gentle decline
• Part of the ocean basin, not part of the
  continent
• Submarine Canyons
• Underwater canyons that extend from the mouths of
  rivers
• Perhaps began when ocean levels were lower????
• Some submarine canyons are hard to explain
  because they are too deep to ever be under the
  water and are not hooked up with a present day
  river
• Currents?
• Mudslides?

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23.2 Continental Margin
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23.2 Continental Margin

• Active Margins
• Continental shelf is very narrow and ends in a
  trench or a sliding boundary
• Where???
• Passive Margins
• Continental shelf is very wide with no trenches
  or rugged coastal mountains
• Where???

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Label Active and Passive Margins
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23.3 The Ocean Basin

• Abyssal Plain
• The flattest surface on earth
• Made of sediments
• Sludge is up to 1 km thick
• Carried there by turbidity currents
• Many plains are found in the Atlantic Ocean
• Abyssal Hills
• Small rolling hills
• Found next to spreading boundaries
• Sometimes are covered by sediments and look like
  Abyssal Plains

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23.3 The Ocean Basin

• Deep-Sea Trenches
• Long, narrow, steep sided troughs that run
  parallel to active continental margins or
  parallel to Island Arcs
• Thousands of km long but not very wide
• Caused by subducting boundaries
• Deepest places on earth and many are unexplored
• Deep-Ocean Vents
• An underwater geyser caused by seawater moving
  through cracks in the crust, hitting magma, and
  then being blown out through cracks

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23.3 The Ocean Basin

• Mid-Ocean Ridges
• Great undersea mountain ranges
• These ranges wrap all the way around the planet
• They occur at spreading boundaries around a rift
  valley
• Fracture zones are breaks in the crust
  (strike-slip faults) that make up different
  chains of mountains

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23.3 The Ocean Basin

• Seamounts
• Cone-shaped mountain peaks that rise high above
  the ocean floor but are still below the surface
  of the water
• Occur in clusters
• Found all over
• Guyots a seamount with its top sliced off
• Currents???
• Coral Atolls
• Ring shaped coral island that forms around a
  sea mount
• Occur when a volcanic island sinks and leaves a
  coral reef present
• A lagoon is left inside of the reef

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23.3 The Ocean Basin
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• See visualizations
• Read about Neptune project (p. 522)
• Neptune project
• http//www.neptune.washington.edu/

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23.4 Ocean Floor Sediments

• Origins of Sediments (3 categories)
• Terrigenous sediments
• Come from continental rocks and minerals
• Carried by wind and water from land
• Larger particles fall quickly (gravel to sand)
• Smaller particles take longer and change as they
  drop
• Some particles are dropped by icebergs
• Biogenous sediments
• Come from living sources
• Calcareous oozes
• Cover half of the oceans floor
• Shells and skeletons of protists
• Siliceous oozes
• Have a sand base
• Hydrogenous sediments
• Come from chemical reactions
• Manganese nodules are the best examples
• Form slowly like a pearl

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23.4 Ocean Floor Sediments

• Importance of Sediments
• Valuable minerals ?????
• oil
• Record of past world events such as
• Volcanic eruptions
• Ice ages
• Climate changes