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Physical Oceanography

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 Oceanography

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  1. Physical Oceanography Unit II

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

  3. 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.

  4. 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)

  5. 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.

  6. 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.

  7. 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.

  8. Methods of Temperature Measurement • Expendable Bathythermograph (XBT) It is launched from a ship. It records temperature as it falls and depth (by measuring density).

  9. 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.

  10. 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.

  11. 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.

  12. 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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