The Origin of Ocean Basins

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Surface and bottom topography of the oceans
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• How do we measure seafloor topography?
• Why is ocean bathymetry important?

Questions
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What does it mean to be at an altitude of
4000m? It means that I am 4000m above the
Mean Sea Level (MSL) Then, what sets the mean
sea level ?
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Geoid of a rotating tank

• Geoid the shape of mean sea level
• Centrifugal force pulls up the surface away from
  the axis of rotation
• Parabolic surface
• Apparent gravity is perpendicular to the tilted
  surface

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Geoid on a spherical planet

• Centrifugal force bulges out the surface away
  from the axis of rotation
• Geoid ellipsoid
• Apparent gravity is deflected outward
• The Earths geoid has irregularities due to
  spatially varying gravity (shape) of the planet

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Geoid reflects seafloor topographic features
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What sets the Earths geoid?

1. The spin of the planet ? Ellipsoid
2. Irregular seafloor topography ? Local changes
   in gravity

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Measuring seafloor from space
Reading material on Class Website Satellite
Topography and Oceanography from Space
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Satellite can measure the height of ocean surface
very accurately The shape of surface ocean
reflects spatially varying gravity of the
planet Seafloor topography can be calculated
based on the irregularity of gravity field
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Why ocean bathymetry?

• Tsunami prediction
• Ocean current, climate studies
• Offshore resource development
• Submarine cables for telecommunication
• International boundaries

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Ocean Circulation and Climate Heat Transport
affected by topography!
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Ocean Circulation and Climate Ocean Currents
take different paths!
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Ocean Circulation and Climate Deep ocean mixing
and pathways
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Ocean Circulation and Climate Mixing energy and
dissipation of tides!
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Ocean Circulation and Biology Seamounts .
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Societal impacts Tsunami
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Societal impacts Gas and oil extraction