While on my 4-wheeler riding around in the wood in Lakewood Wisconsin I came upon a puddle with a green film in it in the middle of a dirt road and I drove up to check it out and I am glad I did! As I was dismounting from my 4-wheeler colors on the puddle caught my attention and I found the same thing Marko Riikonen found algal optics. Over the period of 10 minutes or more I observed corona similar to pollen corona around sun’s reflection and Quetelet rings which I have always wanted to see. I also saw glory with the similar brightening’s like pollen corona and a white fogbow like glow around the glory. More pictures here.
Author: Michael Ellestad, Wisconsin, USA
Excavating the literature finally gave confirmation that it is the alga Chromulina rosanoffii that causes Quetelet rings and glory on water surface. This unique sort of alga separates itself from the water surface by forming a stalk on top of which it rests. This is seen in the right hand microphoto which is taken parallel to the water surface. Light blue is air and black is water. On the left is a photo taken at right angle to the water surface, thus giving a look at the C. rosanoffii forest from above (transmitted light). If the alga is for some reason submerged in the water, it sheds its stalk and starts immediately swimming. The b&w photos here show C. rosanoffii submerged in water.
Also two photos of the optical phenomena caused by this alga are displayed in the composite. On the left is a fisheye view with Quetelet rings. The glow around the camera shadow is fogbow. Notice the brightening towards nadir in fogbow, indicating possibly non-spherical particles. The photo on right is taken further away from the cultivation tub, showing spectral colored glory rings. Attached to the outmost glory ring is faint, white fogbow.
All said here about the biology of C. rosanoffii was known long time ago. The alga was described in 1880 by Russian botanist Woronin, who encountered it while visiting Finland. One aspect of the studies carried since has been the golden glow that well developed C. rosanoffii surface film displays, as shown beside and here. But I have not yet met in the literature any mention of the spectral colors, which strikes me as a small wonder. However, there is still plenty of reading to be done, so something may come up.
[Posted by Marko Riikonen]
Jari Piikki have also found some ponds with algal films that show optical phenomena. The ponds were sampled and the alga allowed to breed for some weeks. Extracts were photographed through a microscope. In one pond, Botryococcus alga was abundant nine years ago but then disappeared. Now it is back and quite large Quetelet rings and a corona were visible. Another pond on one island possibly contained Chromulina rosanoffi and microscope images showed it floating on the water surface.
Jari Piikki also found a new optical phenomenon. He took (like Marko) some samples from ponds and cultivated them. In one of them Chromulina disappeared and some other alga appeared. There could be seen a very colourful ring with two zones of spectral colours around the reflection from the surface of the Sun or an artificial light. The ring was oval and became smaller, when the light was brought closer to the water surface. Its diameter in sunlight was about 30 degrees and the inside was dark, so it was not an aureole. also visible when the light shone through the alga from below. Many photographs of the surface were taken with a microscope to show its structure. You can see it in some photos. The alga constantly changes constantly and now shows small colourful blotches.
[Text: Jari Piikki]
Here are some results from the work I have done this summer on the phenomena caused by algal film on water surface.
The upper pair of photographs shows elliptical corona and the alga that caused it. Pine pollen gives the scale. This corona-type display has no other phenomena.
The lower photo shows another type of display, which exhibits Quetelet rings, brightenings around sun””s reflection image, glory and fogbow. In this case there is also unidentified diffuse feature marked with arrows. In addition, fogbow and glory have spot-like brightening towards nadir. Two B&W photos of the algae causing this type of display are shown. In the lower photo the algae are possibly turned 90° in comparison to upper, showing elliptical shape. This species might be Chromulina rosanoffii. It””s about 5-10 µm in size (not to scale with upper color photo) and well transparent to make glory.
These phenomena turned out to be common, at least this summer. They were most abundant on rocky Finnish archipelago islands, which harbour endless number of small rock pools.
[Posted by Marko Riikonen]