Use of a diving bell, ca. 1752 in Britain — an early attempt at marine exploration

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Use of a diving bell, ca. 1752 in Britain an
early attempt at marine exploration
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Ocean Basins

• Bathymetry of ocean floors
• Deep ocean basins
• Continental margins

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Key Concepts

• Seafloor features result from a combination of
• Plate tectonic activity
• Erosion and deposition processes
• Deep sea floor is the ocean basin
• Ocean-continent transition zone is called the
  continental margin
• Sedimentation important process shaping
  architecture

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Ocean Basins Introduction

• 71 of Earths surface is covered by oceans.
• Little has been known about the deep sea until
  very recently
• Methods of study
• Echo sounding and seismic profiling
• Submarine diving
• Dredging, coring, and drilling
• Satellite measurements

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Bathymetry

• Echo Sounding
• Multi-beam mapping
• Satellite Altimetry

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Echo Sounder and swath bathymetry
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Multibeam Bathymetry

• Ultra-high resolution, but labor-intensive

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Bathymetry is topography
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Satellite Altimetry

• Principle sea surface mirrors underlying
  topography because of gravitational effect
• Lower resolution than multi-beam, but covers
  entire ocean

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TOPEX-POSEIDON bathymetry
Seamounts
Abyssal Plains
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Direct Access to Sea Floor
Alvin submersible
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Deep Ocean Drilling
JOIDES Resolution
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Continental margin Deep ocean basin
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Deep-ocean Basins

• More than 1/2 of Earths surface
• All blanketed by sediment except youngest rocks
  at ridges
• 2 main components
• Oceanic ridges
• Abyssal plains

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The Oceanic Crust

• Rocks of the ocean floor differ from continents
• Form by seafloor spreading
• Mid-ocean ridges
• Largest topographic features on Earth
• Divergent plate boundaries
• Elevated due to heat
• Rift valleys
• East Pacific Rise
• Mid-Atlantic Ridge

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Ocean Basins and Abyssal Plains
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Structure of Oceanic Crust
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Ocean Crust composition

• Balsaltic volcanism and gabbro intrusion
• Pillow lavas
• Hydrothermal vents (black smokers)

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• Seafloor Spreading Rate is 2-10 cm/yr
• Mid-Atlantic Ridge is slow
• East Pacific Rise is fast

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Ocean Basins and Abyssal Plains
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Ocean Basins and Abyssal Plains

• Flat, featureless expanses of sediment-covered
  ocean floor
• 3700 to 5500 m depth
• Older crust is cooler, subsides deeper
• Pelagic sediment accumulates
• Biogenic ooze CaCO3 ooze, SiO2 ooze
• Terrigenous fine-grained clays and silts

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Biogenic Ooze

• Calcareous or siliceous
• Radiolarians (SiO2)
• Foraminifera (CaCO3)
• Diatoms (SiO2)
• Form cherts and chalks when lithified

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Deep-ocean Trenches

• Long, relatively narrow features
• Deepest parts of ocean up to 11,000 m deep!
• Most are located in the Pacific Ocean
• Convergent plate boundaries
• Sites where moving lithospheric plates plunge
  into the mantle --gt subduction zones
• Associated with island arc volcanoes

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Continental Margins

• Passive vs. Active Margins
• Continental Shelf
• Continental Slope
• Continental Rise

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• Passive margins do not coincide with plate
  boundaries
• Active margins do coincide with plate boundaries
  (convergent or transform)
• Atlantic has mostly passive
• Pacific has mostly active

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Distribution of Continental Shelves and Slopes
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• Continental Slope surface 5-25 degree slope
• Dissected by submarine canyons
• Transport sediment from shelves down slope to
  deep-sea fans

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Turbidity Currents
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Continental Rise

• Apron of accumulated sediment at base of
  continental slope
• Only on passive margins
• 100 to 1000 km wide
• Gradual slope (1/8 that of cont. slope)

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Active Continental Margins

• Continental slope descends abruptly into a
  deep-ocean trench -- subduction zone
• Located primarily around the Pacific Ocean
• Accumulations of deformed sediment and scraps of
  ocean crust form accretionary wedges

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Active Continental Margins