biology 3709 - light and irradiance in the oceans

8/6/2019 Biology 3709 - Light and Irradiance in the Oceans

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Matthew English & Meghan Donovan


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The Visible Spectrum of Light We can see light with a wavelength from 380nm-750nm.

Photosynthetic organisms only use light that is 400nm-

700nm in wavelength. The energy of light increases as the wavelength decreases.

Picture:http://www.dnr.sc.gov/ael/personals/pjpb/lectur

e/spectrum.gif
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Photic Zone The area of the ocean where enough light can

penetrate to drive photosynthesis.

All aquatic plants are restricted to the photic zone.

In the clearest areas of open ocean, the photic zoneextends down to about 200-300m depth.

But this depth is highly variable and controlled by a

variety of factors such as: Light intensity, water turbidity and the suns angle to the sea

surface.

In highly turbid eutrophic lakes, the photic zone may onlybe a few cm in depth.


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Light Penetration The blue wavelengths penetrate the deepest.

This is due to their lower wavelength and thus higherenergy.


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Productivity Phytoplankton are one of the main primary producers

in the worlds oceans.

They photosynthesize to grow and reproduce, and areeaten by zooplankton to sustain many food webs.

Plants are also important primary producers andsustain much life.

But, productivity varies with the seasons. At mid tohigh latitudes, plant productivity is inhibited in thewinter due to a lack of PAR and winter storms thatremove plants from the photic zone.


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Critical & Compensation Depth Critical depth is the depth at which the net gain of

photosynthetic payoff is zero.

The growth and death rates of primary producers are equal.

Compensation depth is the depth at which the O2produced by photosynthetic organisms is completelytaken up during cellular respiration.

Both these depths are controlled by a variety of factors

(e.g. season, turbidity, latitude, etc).

As the mixed layer of ocean water reduces, primaryproductivity greatly increases because plants are notbeing carried below their critical depth.


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References South Carolina's Department of Natural Resources. (2011).

Photosynthesis. Retrieved from http://www.dnr.sc.gov/ael/

personals/pjpb/lecture/lecture

Herring, Campbell, Whitfield, & Maddock. (1990). Light And Life In

The Sea. New York: University Press, Cambridge.

Gross, G. (1977). Oceanography: A View Of The Earth. Englewood

Cliffs: Prentice Hall Inc.

Segar, D. A. (1998). Introduction To Ocean Sciences. London:

Wadsworth Publishing Company.

biology 3709 - light and irradiance in the oceans

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