The Ocean Floor

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The Ocean Floor

• Chapter 14

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14.1 The Vast World Ocean

• Key Concepts
• How much of Earths surface is covered by water?
• How can the world ocean be divided?
• How does the topography of the ocean floor
  compare to that on land?
• What types of technology are used to study the
  ocean floor?
• Vocabulary
• Oceanography, bathymetry, sonar, submersible

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• What do you think you the bottom of the ocean
  would look like if all the water were drained
  away?

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• The Blue Planet
• About 71 of the Earth is covered by the global
  ocean.
• Oceanography is the study of oceans, and draws on
  geology, chemistry, physics, and biology.

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• Geography of the Oceans
• Earth510 000 000 km2
• 360 000 000 km2 oceans
• 150 000 000 km2 Continents and Islands
• Lumberton 40.8 km2
• The global ocean can be divided into four main
  ocean basins Pacific Ocean, Atlantic Ocean,
  Indian Ocean, and Arctic Ocean.

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• Pacific Ocean
• Largest geographic feature on Earth
• Worlds deepest ocean, average depth of 3940 m
• Atlantic Ocean
• About half the size of the Pacific Ocean
• Indian Ocean
• Slightly smaller than the Atlantic Ocean
• Almost entirely in the southern hemisphere
• Arctic Ocean
• About 7 the size of the Pacific Ocean
• About 25 as deep as the other oceans

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Reading Checkpoint

• What are the four main ocean basins?

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• Mapping the Ocean Floor
• The topography of the ocean floor is as diverse
  as that of continents
• Bathymetry is the measurement and charting of
  ocean depths
• Bathydepth, metrymeasurment

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• Sonar
• Sonar is an acronym for Sound Navigation And
  Ranging
• A sound wave is sent towards the ocean floor.
  When it hits, it bounces back to the boat.
• Measuring the time between sent and received will
  give you a profile of the ocean.

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• Satellites
• Using satellites scientist found that the ocean
  surface is not perfectly flat.
• Large features (ocean mountains, or trenches)
  cause elevation or depression in the ocean
  surface.
• Satellites send radar waves which bounce off the
  ocean and return to the satellite.
• Measuring the time between send and receive gives
  an idea of the ocean surface.
• Satellites and Sonar are used together to produce
  ocean floor maps.

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Reading Checkpoint

• How do satellites help us learn about the shape
  of the seafloor?

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• Submersibles
• Due to extreme pressure humans can only dive so
  far.
• Submersibles (manned or unmanned) are used to go
  farther.
• These are used to take pictures, videos, and
  samples from deep waters.
• ROVs are unmanned Remotely Operated Vehicles.
• These can stay submerged for longer periods of
  time.

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14.1 Mini-Quiz

• How much of Earths surface is covered by water?
• What are the four main ocean basins?
• Which ocean is deepest and which ocean is the
  shallowest?
• How does the topography of the ocean floor
  compare to that on land?
• What types of technology are used to study the
  ocean floor?

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14.1 Section Assessment

• Answer 1-7 on page 400 in complete sentences.

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14.2 Ocean Floor Features

• Key Concepts
• What are the three main regions of the ocean
  floor?
• How do continental margins in the Atlantic Ocean
  differ from those in the Pacific Ocean?
• How are deep-ocean trenches formed?
• How are abyssal plains formed?
• What is formed at mid-ocean ridges?
• Vocabulary
• Continental margin, continental shelf,
  continental slope, submarine canyon, turbidity
  current, continental rise, ocean basin floor,
  abyssal plains, seamounts, mid-ocean ridge,
  seafloor spreading

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• The ocean floor has three main regions
• Continental margins
• Ocean basin floor
• Mid-ocean floor

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How do the regions compare?
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• Continental Margins
• Continental margin is the transition zone between
  the continent and the ocean basin floor.
• In the Atlantic Ocean thick sediments cover the
  wide continental margin, because the margin is
  not geologically active.
• In the Pacific Ocean one plate sinks below
  another causing volcanic and earthquake activity.
  Thus you have a narrow continental margin.

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• Continental Shelf
• The continental shelf is the gently sloping
  submerged surface extending from the shoreline.
• It may be very narrow or extend as far as 1500km
  (312 trips from school to Wal-Mart and back)
• The slope is so gentle it appears flat to the
  human eye
• Continental shelves contain important mineral
  deposits, large reservoirs of oil and natural
  gas, huge sand and gravel deposits, and fishing
  grounds.
• But we must be careful how we harvest these
  resources.

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• Continental Slope
• The continental slope is steeper than the shelf.
• Relatively narrow
• Deep sided valleys known as submarine canyons are
  cut into the continental slope by turbidity
  currents.
• Turbidity currents are movements of dense,
  sediment rich water down the continental slope.
• This water is denser and so it sinks and erodes
  the slope as it goes.
• Turbidity currents erode submarine canyons and
  deposit sediments on the deep-ocean floor.

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• Continental Rise
• The slope merges with a more gradual incline
  called the continental rise.
• The rise is not very steep, and may be hundreds
  of km wide.

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• Extending out from a continent's edge is a gently
  sloping, shallow area called the continental
  shelf (F). 
• At the edge of the shelf, the ocean floor drops
  off in a steep incline called the continental
  slope (A).  The continental slope marks the true
  edge of the continent, where the rock that makes
  up the continent stops and the rock of the ocean
  floor begins. 
• Beyond this slope is the abyssal plain (C), a
  smooth and nearly flat area of the ocean floor. 
• In some places, deep, steep-sided canyons called
  trenches (G) cut into the abyssal plain. 
• A continuous range of mountains called the
  mid-ocean ridge (D) winds around Earth. 
• There are mountains on the abyssal plain, too. 
  Some reach above the ocean surface to form
  volcanic islands (E).  Others, called seamounts
  (B), are completely under water.

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Reading Checkpoint

• Compare and contrast the continental slope and
  continental rise.

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• Ocean Basin Floor
• The ocean basin floor lies between the
  continental margin and the mid-ocean ridge.
• Nearly 30 of Earths surface.
• This region includes deep-ocean trenches, flat
  areas called abyssal plains, and tall volcanic
  peaks called seamounts and guyots.

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• Deep-Ocean Trenches
• Trenches form at convergent plate boundaries.
• Where one plate subsides under another plate.
• West coast of USA
• Areas of convergence are associated with
  volcanoes and earthquakes.
• The abundance of activity around the Pacific give
  it the name Ring of Fire
• The deepest known place on Earth is the
  Challenger Deep in the Mariana Trench at 11,022
  meters below sea level.

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Pacific Ring of Fire
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• Abyssal Plains
• Abyssal plains are deep, extremely flat features.
• Thick layer of sediments cover the rugged ocean
  floor.
• These sediments come from turbidity currents and
  settle out of ocean water.

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• Seamounts and Guyots
• Seamounts are volcanoes that have not reached the
  surface.
• Found in all oceans, but the greatest number is
  in the pacific ocean.
• The Hawaiian-Emperor Seamount chain stretches
  from the Hawaiian Island to the Aleutian Trench
• Guyots are once active, now-submerged,
  flat-topped structures.

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• Guyots are once active, now-submerged,
  flat-topped structures.
• Over time the ocean erodes the volcano top to sea
  level
• Over millions of years the islands sink
• This occurs as the tectonic plate carries the
  mount away from the hotspot

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Reading Checkpoint

• What are abyssal plains?

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• Mid-Ocean Ridges (MOR)
• Near the center of most ocean basins
• Longest topographic feature on Earth.
• 70,000 km
• Ranges from 1,000 to 4,000 km in width
• The MOR is segmented by transform faults
• Where the plates slide past one another
  horizontally.

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• Seafloor Spreading
• The MOR is home to a high amount of volcanic
  activity
• As magma rises between two divergent plates it
  cools and forms new seafloor.

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• Hydrothermal Vents
• Hydrothermal vents are places where mineral-rich
  water escapes through cracks in oceanic crust.
• Organisms live here by a process of
  chemosynthesis.
• Hydrothermal vents provide heat and energy source
  for primary producers since sunlight doesnt
  reach this far.

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Understand Earth pg 406 Explaining Coral
Atolls-Darwins Hypothesis

• At what latitudes are the majority of Earths
  coral reefs found?
• What does Darwins hypothesis of atoll formation
  imply about the relationship between the rate of
  growth of coral reefs and the rate of subsidence
  of volcanoes?
• According to the theory of plate tectonics, what
  would cause a volcano to sink below the ocean
  surface?

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14.2 Starter

• Compare and contrast the continental slope and
  continental rise.
• What are abyssal plains?
• What is formed at mid-ocean ridges?
• What is the Pacific ocean nicknamed and why?
• How are trenches formed?

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Section 14.2 Assessment

• Using complete sentences answer 1-7 on page 405

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14.3 Seafloor Sediments

• Key Concepts
• What are the three types of ocean-floor
  sediments?
• What does terrigenous sediment consist of?
• What is the composition of biogenous sediment?
• How is hydrogenous sediment formed?
• Vocabulary
• Terrigenous sediment, biogenous sediment,
  calcareous ooze, siliceous ooze, hydrogenous
  sediment

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Seafloor Sediments

• Coarser sediments settle onto the continental
  shelf and slope.
• Finer sediments (like clay) settle onto the
  deep-ocean floor.

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Why is it more common to find fine-grained
sediment in the deepest areas of the ocean basins?
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• What types of terrigenous sediments are shown on
  the map?
• How do the locations of two types of terrigenous
  deposits differ?
• According to the map, which type of biogenous
  sediment appears to be more common?
• Which type of sediment is found along the west
  coast of North America? The east coast of North
  America?

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• Types of Seafloor Sediment
• Seafloor sediments are often a mix of sediment
  types
• Types of seafloor sediments
• terrigenous,
• Biogenous
• Hydrogenous

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• Terrigenous Sediment
• Terra- earth or land -genous origin
• Terrigenous from land
• Terrigenous sediments originate on land
• Mostly mineral grains eroded from continental
  rocks
• Larger grains settle quickly near the shore
• But smaller grains settle very slowly and may be
  carried very far from shore

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• Biogenous Sediment
• Bio- life
• Biogenous from life
• Biogenous sediments come from living organisms
• Shells
• Skeletons of animals and algae
• Calcareous ooze is produced from the calcium
  carbonate shells of organisms dissolving in ocean
  water.
• Doesnt accumulate in deeper ocean basins
• Siliceous ooze primarily composed of shells from
  diatoms and radiolarians
• These shells are made of silica.
• Phosphate rich sediments come from the bones and
  scales of fish and other organisms.

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Reading Checkpoint

• Name two types of biogenous sediments?

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• Hydrogenous Sediment
• Minerals that crystallize directly from ocean
  water.
• Manganese nodules are rounded, hard lumps of
  manganeses, iron or other metals they form
  around sand particles
• Can be up to 20 cm in diameter
• Calcium carbonates form by precipitation in warm
  waters
• If it is buried it can form a type of limestone.
• Evaporites (or salts) form as water evaporates
• The ocean water becomes saturated with dissolved
  minerals.

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14.3 STARTER

• What are the three types of ocean-floor
  sediments?
• What does terrigenous sediment consist of?
• What is the composition of biogenous sediment?
• Name two types of biogenous sediments.
• How is hydrogenous sediment formed?

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14.3 Section Assessment

• Using complete sentences answer 1-6 on page 409.
• Complete table below.

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14.4 Resources from the Seafloor

• Key Concepts
• Which ocean resources are used for energy
  production?
• How are gas hydrates formed?
• What other resources are derived from the ocean?
• Vocabulary
• Gas hydrates, manganese nodule

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Resources from the Seafloor

• Energy Resources
• Oil and natural gas are the main energy products
  currently being obtained from the ocean floor.
• Other resources have potential as technology
  improves.

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• Oil and Natural Gas
• Ancient remains of organisms that are buried and
  changed to oil and natural gas over millions of
  years.
• Offshore drilling has increase from trace amounts
  in the 1930s to 30 of todays oil.
• Many offshore oil sources are likely.
• But can we access this oil safely, without
  endangering the environment?

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Offshore Reserves

• Persian Gulf
• Gulf of Mexico
• Off the coast of southern California

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• Gas Hydrates
• Gas hydrates are compact chemical structures made
  of water and natural gas.
• Most oceanic gas hydrates are created when
  bacteria break down organic matter trapped in
  ocean-floor sediments.
• The bacteria produce gases that are trapped
  between water molecules.
• A disadvantage is they rapidly break down at
  surface temperatures and pressures.
• 20 quadrillion cubic meters of methane are locked
  up in sediments that contain gas hydrates.

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Reading Checkpoint

• What happens when gas hydrates are brought to the
  surface?

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• Other Resources
• Sand and gravel, evaporative salts, and manganese
  nodules are other major resources from the ocean.

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• Sand and Gravel
• - 2nd in economic value only to the petroleum
  industry
• -Sand and gravel can be used for landfill,
  replenish beaches,
• and to make concrete.
• -Sometimes precious materials (gold, diamond)
  can be found in the sand as well.

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• Manganese Nodules
• These nodules contain metals of economic
  importance
• Mining the ocean floor for these nodules is
  possible but not profitable with current
  technology

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• Evaporative Salts
• As sea water evaporates the concentration of
  dissolved salts increases until they precipitate
  into crystals.
• The most important is halite or table salt.

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14.4 Quiz

• Which ocean resources are used for energy
  production?
• How are gas hydrates formed?
• What happens when gas hydrates are brought to the
  surface?
• What other resources are derived from the ocean?
• What is the mineral name for table salt?

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14.4 Section Assessment

• Using complete sentences answer 1-6,8 and
  connecting concepts.