Transcript Document

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What does the bottom of the
ocean look like?
OR
What is the topography or
bathymetry of the ocean floor?
Topography of the Ocean
Floor
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• echo soundings (1920’s)
• ocean was not deepest in the center
• deepest part of the ocean lie near its edges
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Fig 4-2a, p.67
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Fig 4-3a, p.67
An echo sounder trace. A sound pulse from a ship is reflected off the seabed and returns to the ship. Transit time provides a measure
of depth. For example, it takes about 2 seconds for a sound pulse to strike the bottom and return to the ship when the water depth is
1,500 meters (4,900 feet). Bottom contours are revealed as the ship sails a steady course. In this trace, the horizontal
axis represents the course of the ship, and the vertical axis represents the water depth.
The ship has sailed over a small submarine canyon.
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Fig. 4-2b, p. 67
Ridges/trenches in South Atlantic Sea Floor
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Fig. 4-4c, p. 68
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Bathymetry can tell you where
things are: Oceanic ridge system
Fig nft
BATHYMETRY – OCEAN FLOOR CONTOURS
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Fig 4-5, p.69
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Fnft: The major plates of the earth's crusts
Courtesy of Reto Stockli, NASA Earth Observatory
Atlantic
Ocean
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Fig. 4-17a, p. 78
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Fnft: Some large-scale features of the North Atlantic seafloor
Courtesy National Geophysical Data Center/NOAA
Folded ridges of sediment cover the
ocean floor west of Oregon
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Fig. 4-11, p. 74
Topography of the Ocean
Floor
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REMEMBER:
• deepest part of the ocean lie near its edges
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fnft
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Topography 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 4-6, p.70
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Fig. 4-25, p. 84
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Fig 4-9, p.72
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Florida coast
Fig 4-10, p.73
but
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•There are 2 sides to
every…OCEAN!
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Fig 4-8, p.71
2 types of “margins”
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• PASSIVE MARGIN: Continental margins that
face diverging plates. These do not coincide
with plate boundaries. Little or no activity.
Typically associated with the Atlantic.
• ACTIVE MARGIN: Continental margins that
face converging plates. These coincide
w/plate boundaries. A lot of activity
(earthquake/volcano). Typically associated
with the Pacific.
Continental Margins
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•Passive margins –
– continental margins not located on
plate boundaries
– Atlantic-type margins
Continental Margins
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•Active margins– continental margins on the edge of
convergent or transform plate
boundaries
– Pacific-type margins
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Fig 4-8, p.71
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Fig 4-9, p.72
Continental Margins (Shelves)
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• Width of Continental Shelf is
determined by :
• proximity to a plate boundary
(active margins have narrow
shelves while passive margins
have broad shelves)
Continental Margins (Shelves)
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• Continental Shelves
– Shallow, submerged extension of a
continent
– broad, gently sloping
– 7.4% of earths Ocean area
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Fig nft
Continental (Passive) Margins
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• Shelf break –
– transition between the continental
shelf and the continental slope
There are also changes from the
continental slope (edge of shelf) to
the continental rise (ends at edge of
ocean floor).
Continental Margins
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• Continental Slopes
– Steeper than the shelf
– end at the deep ocean
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Fig 4-9, p.72
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Fig 4-9, p.72
Continental Margins
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• Continental rises
– at the base of continental slope
– covered by a blanket of accumulated
sediment
– gradual slope
Continental Margins
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• Submarine Canyons
– cut into the continental shelf and
slope
– formed by turbidity currents
(avalanche-like sediment movements)
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F 4.12
Submarine
Canyon
Off of
The coast
Of New
Jersey
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Fig 4-13, p.75
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Mid-Atlantic Ridge between
Florida and western Africa
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Canyon in middle
of ridge
Fig. 4-17b, p. 78
Ocean Basin
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• thick layer of sediment (up to 5 km or 3mi
thick) covering basaltic rocks
• Make up more than ½ of the earth’s surface
Ocean Basin
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• Oceanic ridges
– Underwater mountain chain
– an active spreading center
– offset at regular intervals by transform
faults
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WHERE THE RIDGES ARE!
Fig nft
• Midoceanic Ridge Province consists of a continuous submarine mountain
range.
• It covers about one third of the ocean floor.
• It extends for about 60,000 km around the Earth.
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Examples of what “exists” on the
Ocean Floor
• Hydrothermal Vents
• SeaMounts
• Guyots
• Abyssal Hills
• Abysall Plains
• Trenches
• Island Arcs (seen above “land”)
Ocean Basin
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• Seamounts
– Inactive volcanoes that do not rise above
the surface of the ocean
– They are tall with steep slopes
Ocean Basin
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• Guyots
– Flat-topped seamounts that were eroded
by wave action
• Abyssal Hills
– abundant, small sediment-covered extinct
volcanoes
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guyots (G) and seamounts
Fig. 4-23a, p. 82
Ocean Basin
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• Island Arcs
– Curving chains of volcanic
islands and seamounts
found paralleling the edge
of trenches
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Fig 4-23, p.76
Coral Reefs?
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• All of these different land/(under)water
formations can yield MANY different types of
coral reefs (a very diverse, valuable, marine
community) too!
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Fnft
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Fnft
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Fnft
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Fnft
Ocean Basin
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• Abyssal Plains
– Flat, featureless, sediment-covered ocean
floor
• Trenches
– Arc-shaped depression in the deep
seafloor
– a converging oceanic plate is subducted
• Deep Ocean Province is between the continental margins and the midoceanic ridge .
• It includes a variety of features from mountainous to flat plains:
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–
–
–
–
Abyssal plains
Abyssal hills
Seamounts
Deep sea trenches
Ocean Basin
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• Hydrothermal vents
– average temp is about 8-16oC (46-61oF)
much warmer than the typical 3-4oC (3739oF)
– support a unique community of organisms
that depend on bacteria
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Cross-section of a ridge axis and the plumbing connected to a vent
chimney
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Fig 4-20, p.80
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Sidescan sonar image overlaid onto multibeam bathymetry
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Approximate locations of confirmed hydrothermal vents and cold seeps
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Red-plumed tube worms
Courtesy of Monika Bright, University of Vienna, hydrothermalvent.com
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A black smoker on the Galápagos Rift Zone.
Courtesy of UCSB, University S. Carolina, WHOI/NOAA
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Fig 4-19, p.79