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Topic: Properties of the Ocean

Theme: Energy

Key Concepts:

Waves

  • A wave has both kinetic (moving) and potential (stored) energy.
  • Total wave energy of the oceans is the result of adding together the energies of different types of waves.
  • Once waves are created, they must have a restoring force to sustain wave motion, but waves must be formed initially by a displacing force.
  • Two restoring forces--gravity and surface tension--act on all waves.
  • Planetary waves (Kelvin, Rossby, Equatorial, and Yanai waves) depend on the rotation of Earth for a restoring force.
  • Surface waves are the waves that eventually break on the beach. The restoring force is due to the large density contrast between air and water at the sea surface.
  • Internal waves are subsea waves and are similar to surface waves in some respects. The restoring force is due to vertical density gradients within the sea.
  • Most waves are created by interactions of winds with the water surface. Waves can also be created by:
    • Impacts on ocean water (earthquakes, volcanic explosions, seafloor slumps, etc.)
    • Gravitational attraction between Earth, moon, and sun and
    • The passage of vessels or marine animals through the sea surface.
  • Impacts can create waves (with very long periods) called tsunamis (seismic waves). Tsunami are occasional events and contribute only a fraction of the total wave energy of the oceans, but they can be extremely destructive.
  • Winds never blow uniformly over the water because they are highly variable both in time and space. This variablility is visibly apparent to the ocean observer. Here are some descriptions:
    • "Sea" - waves of different heights, wave-lengths, and directions of travel
    • Calm - waves are insignificant and the sea is flat
    • Swell - waves are smooth, mostly of same wavelength and from same direction.
  • The maximum height of waves depends on wind speed and the length of time the wind blows. It also depends on wind fetch, which is the distance over which it blows.
  • The highest ocean waves are created when winds are strong and blow persistently over long fetches.
  • Steep-sided waves can be created when waves travel in the direction opposite that of a strong ocean current. These waves create hazards for shipping lanes.

Heat

  • Three sources of heat have influence on the ocean:
    • Solar energy
    • Geologic sources:
      • Heat generated by the radioactive decay of elements with Earth,
      • Heat left over from Earth's formation, and
    • Human-induced through the burning of fossil fuels.
  • Solar energy is by far the most important because it is responsible for 3,200 times the contribution of the other two.