Homework 3 Solutions

Lets take that to be at 23 there are two contributions

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Unformatted text preview: to as the aphotic zone, and our estimate is pretty close. In some places the depth is less due to material in the water (next question!) and in others Rayliegh scattering will add more light to deep depths. In any case, at these depths, sea animals are commonly bioluminescent and there is little if any photosynthetic activity. (c) [10 pt] Oceans, lakes and rivers are rarely clear as silt and other material is in suspension in them. Assume a suspension of clay, which has a mass density of 3 g/cm3, with a volume fraction of 10 ppm (parts per million). If you can see your hand only 1 foot into the water, what is the (visible) absorption coefficient of clay? In these case we are not looking for the point where the water becomes dark, but when the majority of photons come from a layer above our hand – the “photosphere”. Let’s take that to be at τ = 2/3. There are two contributions to opacity in this case: Water: |τ| = κλρs = (10 ­4 m2/kg)(103 kg/m3)(0.3 m) = 0.03 – a negligible contribution Silt: The effective mass density of silt in the water is ρeff = 10 ­5ρclay = 0.03 kg/m3 => κλρs =...
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