ColorAcademy 2005 - Underwater

Underwater

One of the earliest scientific observations of the colours of seawater was recorded by Charles Darwin in the narrative of his voyage round the world in HMS Beagle. For example, when not far from the Abrolhos Islands, he said ‘My attention was called to a reddish brown appearance in the sea.

"The whole surface of the water, as it appeared under a weak lens, seemed as if covered by chopped bits of hay with their ends jagged. . ."

According to Dr. Collingwood this was the otherwise yellow and brown organism, Trichodesmium. Darwin further noted along the coast of Chile, saying ‘Some of the water placed in a glass was of a pale reddish tint, and, examined under a microscope, was seen to swarm with minute animalculae, darting about, and often exploding. They were exceedingly small and quite invisible to the naked eye, only covering a space equal to the square of one thousandth of an inch.’. Darwin also mentions the staining of the sea red by crustacea, and by red clay ‘as dark as chocolate’.

By contrast, the naturalist to HMS Challenger, John James Wild, sums up the results of his investigations into the causes of the colour of the sea, and the apparent discoloration of the seawater in certain areas of the ocean: ‘the various tints of blue and green which constitute what may be called the proper colour of seawater, are due to a greater or lesser proportion of salt held in solution, the colour being an intense blue when the water is very salt, and changing by degrees to a green-blue, or blue-green, and green colour as the water becomes more fresh. On the other hand, the abnormally coloured red, yellow, brown, and inky seas owe their appearance accumulation of large masses of seaweeds, from the gigantic algae, which fringe the shores of oceanic islands to the microscopic Diatoms; but almost as frequently the discolouration is caused by myriads of animal organisms collected in shawls at the surface of the ocean.’ Wild also calls attention to the phosphorescent effects – the large globes of mysterious light which ‘phantom-like, rise and fall within the receding waves’ caused by a variety of small crustaceans. The most dazzling display of phosphorescence caused by Pyrosoma, a jelly like cylindrical mass, measuring from two to ten inches in length with a chamber from one to two inches and forming a colony of animals. Wild was also interested in exploring why such places as the ‘Red Sea’, the ‘Yellow Sea’, the ‘Blue Sea’, the ‘White Sea’, where so called. Sometimes the name referred to the land rather than the water, the gloomy coasts of the Black Sea, for example, and the ice forming shores of the White Sea.