PHYSICAL OCEANOGRAPHY Part 4: Light in the Ocean

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PHYSICAL OCEANOGRAPHYPart 4 Light in the Ocean

• GEOL 1033
• (Lesson 29)

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Atmospheric Profile

• Stratification
• Radiation types
• Radiation shields
• Ionosphere
• Ozone
• Surface interactions

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Sunlight Penetration into Seawater

• Photic zone goes down to about 200 m

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Sunlight Absorption in Water as Depth Increases

• Note wavelengths remaining at greater depths

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Measuring Light Penetration

• Secchi disc is lowered until no longer can see,
  indicating the clarity of the water.

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Why is ocean blue?

• Blue penetrates clear seawater more than red,
  orange, yellow, so blue is more available for
  scattering, so open ocean waters are blue.
• Also, on a clear weather day, blue of
  blue-coloured sky is reflected of ocean surface.
• Scattering
• Coastal waters have different colours because of
  sediment suspended in them
• Blue green are absorbed more in turbid waters
• Green absorbed less than blue, so continental
  shelf waters may appear greenish
• Longer wavelengths favoured, so red, orange,
  yellow waters along many coasts (compare to
  rivers)

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