Scientific American 6, 16.10.1858
It is a commonly observed fact that the usual color of the ocean is a bluish green, of a darker tint at a distance from land, and clearer towards the shores. According to Dr. Scoresby, the hue of the Greenland sea varies from ultramarine blue to olive green, and from the purest transparency to great opacity. The surface of the Mediterarnean, in its upper part, is said to have, at times, a purple tint. In the gulf of Guinea the sea sometimes appears white, about the Maldive islands black, and near California it has a reddish appearance. Various causes must, of course, co-operate to produce this diversity of tint. The precailing blue color is generally ascribed to the greater refrangibility of the blue rays of light, which, by reason of that property, pass in greatest abundance through the water. The other colors are ascribed to the existence of vast numbers of minute animalculae - to marine vegetables at or near the surdace - to the color of the soil - the infusion of earthy substances - and very frequently the tint is modified by the aspect of the sky. The phosphorescent, or slimy appearance of the ocean, which is a common phenomenon, is also ascribed to animalculae and to semiputrescent matter diffused through the water.
The temperature of the ocean also exhibits some peculiar and interesting phenomena. Within the tropics the mean temperature at the surface is about 80° Fah., and generally ranges between 77° and 94deg;. At great depths the temperature is probably nearly the same under every latitude. In the torrid zone it is found to diminish with the depth, while in the polar seas it increases with the depth; and about the latitude of 70° it is nearly constant at all depths. But the small number of observations which have yet been made on this subject do not indicate any uniform law, according to which the variations of temperature at different depths is regulated.