1922 Encyclopædia Britannica/Oceanography

OCEANOGRAPHY (see ).—The period following the year 1910 was not productive of notable additions to knowledge of general oceanography. Several expeditions were made just before that year and in the period between then and the World War. The most important were: the Australian Antarctic expedition of 1911–4 under Sir Douglas Mawson; the Danish Oceanographical expeditions in the Mediterranean and adjacent seas of 1908–10; a short cruise made by Sir John Murray and Dr. Johan Hjort in the Norwegian Fishery exploring vessel “Michael Sars” in 1910, the general results of which were published as The Depths of the Ocean (1912) by the leaders of the expedition; and a short special cruise made by the “Scotia” in 1913 (after the loss of the “Titanic”) under the leadership of Dr. Matthews, which made observations upon the distribution of ice in the North Atlantic.

Generally, oceanographic work at sea was brought to a stop by the outbreak of war in 1914. A good deal of special investigation relating to naval and especially submarine warfare was carried on during 1914–8, but the results of this confidential work were not published. The very important activities of the Conseil Permanent International pour l’Exploration de la Mer were suspended during the war except in a few local seas. Fortunately the continuity of the organization was maintained, largely

through the mediation of the British Government, and the council held its first post-war meeting in London in 1920. Its work is primarily that of the investigation of the fisheries of northern Europe, but its general methods are oceanographical, and its published results have formed an immense contribution to the science. Germany and Russia had, temporarily at all events, withdrawn from the coöperation, but France came in for the first time in 1920, and it was understood that the United States was likely to join in the scheme of investigation. An entirely new project was an international survey of the Mediterranean and adjacent seas, from the fishery and oceanographical standpoints, by France, Italy, Spain and Portugal, but in 1921 no definite programme had been put in operation. The International Research Council formed just after the war constituted a section for Physical Oceanography, which held its first meeting in Paris in 1921. In 1920 a very influential movement began, in England, for the despatch of a new “Challenger” expedition on a great scale, but it was suspended in 1921 for lack of funds. On the whole, oceanographical research was being taken up most actively in Europe, but much important work was also begun in America, for instance the fine hydrographical research in the Pacific by the Scripps Institute of the university of California.

Methods of Investigation.—Little change occurred subsequently to 1910 with regard to the methods of oceanographical investigation except a continual refinement and an increasing improvement in the apparatus used: in this direction the activities of the Central Bureau of the International Council were very noteworthy. The instruments—current-meters, sounding apparatus, water-collecting bottles, thermometers, hydrometers, etc.—were all elaborated and improved. Hydrodynamical methods received increased attention and the investigation of the movements of the ocean by means of physico-mathematical devices developed as a result of the older work of Bjerknes, continued chiefly by Helland-Hansen and Sandström. It became fairly certain, however, that theory had outrun observational work, and that the latter must again receive renewed attention.

Variations in Oceanic Circulation.—The general scheme of oceanic circulation was made out prior to 1910. The excess of heat received in equatorial regions expands the water, but at the same time excess of evaporation concentrates it, so that the density increases. The heating effect is, however, the more significant, and so the water of the ocean tends to flow N. and S. from the equator towards the poles. In intermediate latitudes there is a loss of heat and then the increased density due to equatorial concentration becomes a factor. The water sinks below the surface and continues to flow along the sea bottom back towards the equator. In the polar areas the melting of sea-ice and of ice formed by precipitation lowers the density of the sea-water and causes a difference of level which sets up streaming movements towards the equator. This surface drifting water is cold and as it enters into intermediate zones it remains colder

than the water in situ there and is therefore denser; it sinks below the surface and continues to flow along the bottom either back to the polar regions or towards the equator.

This main scheme is complicated in various ways: (1) by the rotation of the earth, which continually deflects currents of water or air to the right in the northern or to the left in the southern hemisphere; (2) by the conformation of the land masses (as in the case of the equatorial stream which is banked up in the Gulf of Mexico and flows out through the Straits of Florida); (3) by the varying depth of the ocean, for currents tend to flow more readily through deep than in shallow waters (as in the case of the main Atlantic drift, which flows most strongly through the deep channel between Shetland and the Faroe Is.); and (4) by the driving force of the winds acting on the surface of the sea (thus the drift of water from the equator is not N.E., as one might expect, but from E. to W., because of the impelling force of the N.E. and S.E. trade-winds).

Long-range Periodicities in Oceanographical Changes.—More and more the science seeks to discover periodicities and to correlate these with others. In these attempts new methods are elaborated and in their criticism contributory phenomena are discovered. An interesting example is the discussion, by Otto Pettersson, of the effects of long-range fluctuations in the tide-generating force: this memoir was published about 1914, but has only recently become available to English readers.

Hydrobiology.—The study of marine life has in recent years become more general, and has become associated with very precise investigations into the chemical composition of sea-water, changes in chemical equilibrium, the effect of variations in salinity and temperature, the processes set up by marine bacteria, and so on. The investigation of the microscopic pelagic life of the sea has also developed to a great extent. Several decades ago all marine organisms became grouped together in three great categories: (1) the Benthos, or bottom-living, rooted or sedentary forms; (2) the Nekton, or actively swimming animals; and (3) the Plankton, or drifting (usually) microscopic organisms, which have little power of locomotion (see ). The plankton is divided into (a) the Zoö-plankton (such as the minute crustacea and the eggs and larvæ of fishes and many other marine animals); and (b) the Phyto-plankton, that is, the minute algae, diatoms, peridinians, some flagellate protozoa, spores of algæ, etc. The investigation of the plankton from a new point of view, begun by Hansen in 1889, was continued by Lohmann at Kiel, by Cleve in Sweden, by Gran and Ostenfeldt in Norway and Denmark, and by Herdman, Allen and others in England. Hansen’s early results were much criticized and the original methods very greatly modified and improved. It became clear that only very rough estimates of the numbers of planktonic organisms in a volume of sea-water as large as (say) 10 cubic metres could be made, but that these estimates could nevertheless be trusted to show very marked regional and seasonal differences.

Coral Formations.—Coral reefs remove calcium from solution in the sea on a vast scale. During recent years the controversies with regard to the modes of formation of these structures have entered on a new phase. The theories of Darwin, Agassiz, Dana, Semper, Murray and others had led to apparently interminable discussion, and the great boring experiments at Funafuti atoll, which were expected to be crucial, gave results that backed both the rival theories of Darwin and Murray. On the other hand, Wayland Vaughan (see Annual Report of the Smithsonian Institution, 1917) has shown clearly that the problem is essentially a biochemical one and may finally be solved by the methods of the latter science.