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Physical Oceanography. Unit II. Physical Oceanography. Physical oceanography is the study of the properties of seawater. There are 4 main topics: Temperature Salinity Density Pressure. Temperature.

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physical oceanography1
Physical Oceanography
  • Physical oceanography is the study of the properties of seawater.
  • There are 4 main topics:
      • Temperature
      • Salinity
      • Density
      • Pressure
temperature
Temperature
  • Water has the highest specific heat (heat capacity) of any liquid: a high amount of energy is needed to raise or lower the temperature of water.
  • As a result, sea water takes a long time to heat up or cool down.
slide4
Earth’s climate is kept moderate because of this property of water.
  • Compare the differences in extremes of temperature on land and water:
    • Land: Libya (64ºC) to Antarctica (-89ºC)
    • Ocean: Persian Gulf (36ºC) to Southern Ocean (-2ºC)
temperature and depth
Temperature and Depth
  • Temperature decreases with depth, but not at a constant rate.
  • On our coast, the surface temperature fluctuates with the season, and the temperature changes only a few degrees from the surface to about 200 m deep.
slide6
Below 200 m, it is too deep for the temperature to be influenced by the sun and temperature drops very rapidly until about 1000 m.
  • This region is called the permanent thermocline.
permanent thermocline
Permanent Thermocline
  • The average ocean temperature is about 4ºC and the average surface temperature is about 18ºC.
  • In the tropics, day and night are about equal in length and the surface temperature rarely falls below 25ºC.
  • In the Arctic, winter nights are long, so water loses a lot of its heat resulting in ice formation.
methods of temperature measurement
Methods of Temperature Measurement
  • Expendable Bathythermograph (XBT)

It is launched from a ship. It records temperature as it falls and depth (by measuring density).

slide9
The XBT is used for depths down to 2000 m (usually 410-760 m).
  • Two very small wires transmit the temperature data to the surface.
  • The probe is designed to fall at a constant rate, so depth can be inferred from time since it was launched.
slide10
2. Niskin Bottles
  • Used for collecting water samples from various depths.
  • Usually arranged in a rosette of up to 36 bottles. Lowered to maximum depth, then pulled up slowly, taking samples in a series as it is raised.
slide11
Can have reversing thermometers along the side to record temperature.
  • A CTD (conductivity, temperature, depth) probe is often attached to the rosette to measure salinity, temperature and pressure all at once as a water sample is taken.
slide12
3. Infra-red Photography
  • From airplane or satellite, for measuring surface temperature over a wide area (ex: North Atlantic on July 15), then colorized.

4. Stationary and Drifting Buoys

  • Data often includes surface and subsurface water temperatures, air pressure, air temperature, wind speed and direction.
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