Occasionally the oceans make themselves felt in a dramatic and often disastrous way; great waves resulting from a submarine earthquake may sweep across a low coastal area, laying it waste, or storm waves may break down sea defences and flood low-lying land, or a ship may be lost at sea. At other times the great ocean streams pass almost unnoticed on their way, the tide ebbs and flows unobserved, and little thought is given to the vital part the ocean plays in life on earth. It is not only because the oceans are vast in area, covering over 70 per cent of all the earth's surface, but because of their own intrinsic interest that they are worthy of closer study.
Enormous quantities of water are moved by some ocean currents; the Gulf Stream, for example, transports more than one thousand times the greatest Mississippi flood from southern latitudes northwards. Modern oceanographical work suggests that its influence on the climate of north-west Europe is very complex; it has been suggested by Iselin that the warming of the climate of this part of Europe may be greater during periods of smaller transport by the Gulf Stream. There are some facts which support this view, although it is no more than an interesting suggestion at the moment.
The oceans pose many fascinating problems. The origin of the ocean basins and the water which fills them is of fundamental importance to an understanding of the global pattern of land and sea. The fluctuations of the level of the oceans has far-reaching effects on land and is at present closely linked to glacier fluctuations and through this to climatic change. Sea-level is also the base level to which subaerial erosion is working, in areas drained by rivers which reach the sea. It is one of the tasks of modern geomorphology to establish the denudation chronology of areas in terms of changes in base level. The response of the rivers to negative changes in base level is clearly dependent on the gradient of the sea floor exposed by the fall in sea-level. Thus the nature of the sea floor close to the land and the oscillations of sea-level are important to geomorphological analysis.
The connexion between the oceans and the climate is an intimate one, the two interacting in many different ways to influence each other. Through the climate, the general character of the land areas is related to the nature of the ocean water and its circulation. Recently new techniques have been devised for the study of the oceans; one of the very interesting and useful ones is a new method of measuring directly . . .