Transcript What does the bottom of the ocean look like? OR What is the topography or bathymetry of the ocean floor?

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What does the bottom of the
ocean look like?
OR
What is the topography or
bathymetry of the ocean floor?
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Fnft: The major plates of the earth's crusts
Courtesy of Reto Stockli, NASA Earth Observatory
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
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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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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Ridges/trenches in South Atlantic Sea Floor
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Figure 3.C
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Bathymetry can tell you where
things are: Oceanic ridge system
Fig nft
Figure 3.6
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BATHYMETRY – OCEAN FLOOR CONTOURS
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Fig 4-5, g
Atlantic
Ocean
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fnft
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Fnft: Some large-scale features of the North Atlantic seafloor
Courtesy National Geophysical Data Center/NOAA
Mid-Atlantic Ridge between
Florida and western Africa
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Canyon in middle
of ridge
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 4-9, g
Figure 3.8
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Florida coast
but
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•What goes UP must
go DOWN!
&
•There are 2 sides to
every…OCEAN!
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Figure 3.7
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Fig 4-7, g
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
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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, g
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Continental Margin:
Continental SHELF
Continental BREAK
Continental SLOPE
Continental RISE
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Fig 4-9, g
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, g
Continental Margins
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• Continental rises
– at the base of continental slope
– covered by a blanket of accumulated
sediment
– gradual slope
Folded ridges of sediment cover the
ocean floor west of Oregon
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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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Submarine
Canyon
Off of
The coast
Of New
Jersey
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What comes next?
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• Where the Continental Slope/Rise (granite
rock) meets the “deep” ocean floor you get a
sediment covered area (Continental Rise)
that meets the “true” ocean floor (basalt
rock)…what do you find there? What does it
look like?
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Fig 4-9, g
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
Figure 3.15
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Ocean Basin
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• Oceanic ridges
– Underwater mountain chain
– an active spreading center
– offset at regular intervals by transform
faults
– You know this as “Sea Floor Spreading”
(divergent plate boundary)
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WHERE THE RIDGES ARE!
Fig nft
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Fig. 4-16a, p. 89
• 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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Other examples of what “exists” on
the Ocean Floor
• SeaMounts
• Guyots
• Abyssal Hills
• Abysall Plains
• Trenches
• Island Arcs (seen above “land”)
• Hydrothermal Vents
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
– (Made of) Basalt!
Ocean Basin
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• Guyots
– Flat-topped seamounts that were eroded
by wave action
• Abyssal Hills
– abundant, small sediment-covered extinct
volcanoes
Both still BASALT!
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guyots (G) and seamounts
Figure 2.26
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Ocean Basin
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• Island Arcs
– Curving chains of volcanic
islands and seamounts
found paralleling the edge
of trenches
– Part of an “Ocean-Ocean”
Convergent Plate Boundary
geographic result
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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
Figure 3.12
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Ocean Basin
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• Trenches
– Arc-shaped depression in the deep
seafloor
– a converging oceanic plate is subducted
(either Oceanic-Oceanic or OceanicContinental Crust)
Figure 3.13
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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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Approximate locations of confirmed hydrothermal vents and cold seeps
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Cross-section of a ridge axis and the plumbing connected to a vent
chimney
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A black smoker on the Galápagos Rift Zone.
Courtesy of UCSB, University S. Carolina, WHOI/NOAA
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Red-plumed tube worms
Courtesy of Monika Bright, University of Vienna, hydrothermalvent.com
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Importance of
Vent Ecosystem Discovery
1.
Life in extreme
environments
2.
Life independent of sun
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Chemosynthesis = a type of primary
production
Photosynthesis  uses sunlight + carbon dioxide  coverts to food
Chemosynthesis  uses sulfur + carbon dioxide  converts to food
Photosynthesis reaction:
CO2 + H2O + sunlight  CH2O + O2
Chemosynthesis reaction:
O2 + CO2 + H2O + H2S  CH2O + H2SO4
where H2S is hydrogen sulfide,
H2SO4 is sulfuric acid, and
CH2O is “food” or organic material
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+
CO2 + H2O
O2 + [CH2O]
PHOTOSYNTHESIS
CHEMOSYNTHESIS
CO2 + H2O + H2S + O2
[CH2O] + H2SO4
Importance of Vent Bacteria
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• Base of vent ecosystem -- chemosynthesis
• Possible origin of life on Earth
• Illustrate link between biology and habitat
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!
Coral Reef Development
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• Fringing reefs – develop
along margin of
landmass
• Barrier reefs – separated
from landmass by lagoon
• Atolls – reefs continue to
grow after volcanoes are
submerged
Coral Reef Development
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Fnft
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Fnft
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Fnft
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Figure 4-6c Present-Day Margin Southeast of Cape Cod
Fnft – Reefs can exist FAR
offshore (relics from years ago)