Physical Geography of the Sea.[40]
CLIMATES OF THE SEA.
The fauna and flora of the Sea are as much the creatures of Climate, and are as dependent for their well-being upon temperature, as are the fauna and flora of the dry land. Were it not so, we should find the fish and the algæ, the marine insect and the coral, distributed equally and alike in all parts of the ocean; the polar whale would delight in the torrid zone; and the habitat of the pearl oyster would be also under the iceberg, or in frigid waters colder than the melting ice.
THE CIRCULATION OF THE SEA.
The coral islands, reefs, and beds with which the Pacific Ocean is studded and garnished, were built up of materials which a certain kind of insect quarried from the sea-water. The currents of the sea ministered to this little insect; they were its hod-carriers. When fresh supplies of solid matter were wanted for the coral rock upon which the foundations of the Polynesian Islands were laid, these hod-carriers brought them in unfailing streams of sea-water, loaded with food and building-materials for the coralline: the obedient currents thread the widest and the deepest sea. Now we know that its adaptations are suited to all the wants of every one of its inhabitants,—to the wants of the coral insect as well as those of the whale. Hence we know that the sea has its system of circulation: for it transports materials for the coral rock from one part of the world to another; its currents receive them from rivers, and hand them over to the little mason for the structure of the most stupendous works of solid masonry that man has ever seen—the coral islands of the sea.
TEMPERATURE OF THE SEA.
Between the hottest hour of the day and the coldest hour of the night there is frequently a change of four degrees in the Temperature of the Sea. Taking one-fifth of the Atlantic Ocean for the scene of operation, and the difference of four degrees to extend only ten feet below the surface, the total and absolute change made in such a mass of sea-water, by altering its temperature two degrees, is equivalent to a change in its volume of 390,000,000 cubic feet.
TRANSPARENCY OF THE OCEAN.
Captain Glynn, U.S.N., has made some interesting observations, ranging over 200° of latitude, in different oceans, in very high latitudes, and near the equator. His apparatus was simple: a common white dinner-plate, slung so as to lie in the water horizontally, and sunk by an iron pot with a line. Numbering the fathoms at which the plate was visible below the surface, Captain Glynn saw it on two occasions, at the maximum, twenty-five fathoms (150 feet) deep; the water was extraordinarily clear, and to lie in the boat and look down was like looking down from the mast-head; and the objects were clearly defined to a great depth.