Bathymetry of the Ocean Floor

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Bathymetry of the Ocean Floor

• echo soundings (1920s)
• ocean was not deepest in the center

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Echo sounding- not always accurate
Fig. 4-2a, p. 79
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Figure 3.1- An Echo Sounding of US East Coast
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Figure 3.3- Side-scan SONAR (Sound Navigation and
Ranging)
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Figure 3.2- Multibeam SONAR (Sound Navigation And
Ranging)
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Satellites Can Be Used to Map Seabed Contours
With the use of satellite altimetry, sea surface
levels can be measured more accurately, showing
sea surface distortion. (left) Distortion of the
sea surface above a seabed feature occurs when
the extra gravitational attraction of the feature
pulls water toward it from the sides, forming a
mound of water over itself.
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Figure 3.B
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Figure 3.C
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Figure 3.5
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Figure 3.6
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Fig. 4-5, p. 82
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Figure 3.7
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Shape of the Ocean Floor

• shallow extensions of the continents extended
  seaward underwater

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Figure 3.8
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Shape of the Ocean Floor

• Submerged outer edge of the continents are called
  continental margins
• Deep-sea floor beyond these is called the ocean
  basin

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Fig. 4-7, p. 83
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Continental Margins

• Passive margins
• continental margins not located on plate
  boundaries
• Atlantic-type margins

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Continental Margins

• Active margins-
• continental margins on the edge of convergent or
  transform plate boundaries
• Pacific-type margins

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Fig. 4-8, p. 84
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Figure 3.7
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Continental Margins

• Continental Shelves
• Shallow, submerged extension of a continent
• broad, gently sloping

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Figure 3.8
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Fig. 4-9, p. 85
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Continental Margins

• Width of Continental Shelf is determined by
• proximity to a plate boundary
• current speed in the region
• sea-level

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Fig. 4-8, p. 84
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Continental Margins

• Shelf break
• transition between the continental shelf and the
  continental slope
• Occurs at about 140m (360 ft)
• Continental Slopes
• Steeper than the shelf

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Figure 3.8
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Continental Margins

• Continental rises
• base of continental slope covered by a blanket of
  accumulated sediment
• gradual slope
• on Passive margins only

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Fig. 4-9, p. 85
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Fig. 4-7, p. 83
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Figure 3.6
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Continental Margins

• Submarine Canyons
• cut into the continental shelf and slope
• formed by turbidity currents (avalanche-like
  sediment movements)

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Figure 3.10a
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Submarine Canyon Off of The coast Of New Jersey
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Figure 3.11
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Ocean Basin

• thick layer of sediment (up to 5 km or 3mi thick)
  covering basaltic rocks
• Make up more than ½ of the earths surface

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Ocean Basin

• Oceanic ridges
• Underwater mountain chain
• an active spreading center
• offset at regular intervals by transform faults

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Fig. 4-16a, p. 89
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Figure 3.15
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Figure 3.19
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Ocean Basin

• Hydrothermal vents
• 1977 Robert Ballard J F Grassle
• average temp is about 8-16oC (46-61oF) much
  warmer than the typical 3-4oC (37-39oF)
• support a unique community of organisms that
  depend on chemosynthetic bacteria

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Figure 3.17
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Fig. 4-19, p. 91
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Figure 2.26
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Ocean Basin

• Seamounts
• Inactive volcanoes that do not rise above the
  surface of the ocean
• They are tall with steep slopes
• Guyots or Tablemounts
• Flat-topped seamounts that were eroded by wave
  action
• Abyssal Hills
• abundant, small sediment-covered extinct volcanoes

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Ocean Basin

• Abyssal Plains
• Flat, featureless, sediment-covered ocean floor

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Figure 3.12
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Ocean Basin

• Trenches
• Arc-shaped depression in the deep seafloor
• a converging oceanic plate is subducted

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Figure 3.13
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Figure 3.14
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Fig. 4-25, p. 96
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Ocean Basin

• Island Arcs
• Curving chains of volcanic islands and seamounts
  found paralleling the edge of trenches

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Figure 3.C