Wednesday, October 20, 2010

Light Attenuation in the Ocean

As light travels through the water column, it is absorbed and reflected by objects that are in the water, like dissolved sediments, ions, and by water molecules themselves. The decrease in surface light at a given depth in the water column is called "Light Attenuation". Light attenuation is an important factor for autotrophic organisms that which depend on a specific wavelength of light to photosynthesize food. These organisms are limited in how deep they can live depending on their specific wavelength of light, as some wavelengths can travel deeper than others. Shorter wavelength high energy waves, such as blue and violet, travel much deeper in the water column than longer wavelength low energy waves, such as red and infra red. Light attenuation is calculated by multiplying the incident (surface) light by the exponential of negative attenuation constant (different for every wavelength) and the depth (in Meters). Written out, Iz= IoE(-KZ). Figure 1, shown below, is a graphical representation of several wavelengths of light and their percent transmittance (amount of remaining surface light) at a given depth.

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