
.topic 20
G. P. Können (KNMI), Polarized light in Nature, Cambridge University Press, Cambridge 1985


.topic 80
Light is a wave of electromagnetic nature. Such a wave always vibrates normally to its direction of propagation. It need not always be so: for instance, such a wave can just as well vibrate perpendicularly to it or at a different angle. Sunlight, for example, has no special preference for the direction in which it vibrates, and the plane of vibration alternates many times per second. Such light is called unpolarized or natural light. It turns out, however, that there is also light with vibrations remaining in one plane. Such light is called (linearly) polarized.



.topic 90
The ecliptic is the line across the sky along which the sun moves in a year


.topic 110
Radially polarized light is light that vibrates in the direction of an imaginary line joining the source to the point of observation


.topic 120
Tangentially polarized light is light that vibrates perpendicularly to an imaginary line joining the source to the point of observation


.topic 240
C. Floor, 'De laagstaande zon' (The low sun), NTT/De Zee, April 1981, reprint no. 56.


.topic 400

Dinoflagellates (Ceratium hirundinella)

The dinoflagella are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well; their populations are distributed depending on temperature, salinity, or depth. About half of all dinoflagellates are photosynthetic, and these make up the largest group of eukaryotic algae aside from the diatoms. Being primary producers make them an important part of the aquatic food chain. Some species, called zooxanthellae, are endosymbionts of marine animals and protozoa, and play an important part in the biology of coral reefs. Other dinoflagellates are colorless predators on other protozoa, and a few forms are parasitic (see for example Oodinium, Pfiesteria).


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.topic 410

Coccolithophore (Emiliania huxleyi)

Coccolithophores are single-celled algae, or phytoplankton, belonging to the haptophytes. They are distinguished by special calcium carbonate plates (or scales) of unknown purpose called coccoliths, which are important microfossils. Coccolithophores are exclusively marine and are found in large numbers throughout the surface euphotic zone of the ocean. An example of a globally significant coccolithophore is Emiliania huxleyi.

Due to their microscopic size and broad distribution of many taxa, coccoliths (calcareous nannoplankton) have become very popular for solving various stratigraphic problems, and many studies have been devoted to that end. Nanofossils are sensitive indicators of changes in the temperature and salinity of the ocean and sea surface water. Quantitative analysis of calcareous nanoplankton assemblages is being employed to reveal such changes.


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