xiv Introduction 



in London in 1873. These important observations were collected in the records 

 of hydrographic offices or of central meteorological offices and scientifically corre- 

 lated. Records of temperature, salinity and currents at the surface, of tides and of the 

 meteorological conditions over the sea w^ere compiled, and the rapid development and 

 the safety of navigation can be attributed not least to this detailed knowledge of sur- 

 face conditions. 



However, ships' journals of merchant marine ships are not sufficient to give a broad 

 comprehension of oceanographic phenomena. Maritime traffic is interested only in 

 the fastest crossing between the continents and the observations recorded in ships' 

 journals are confined very largely to certain routes, usually those that are as short as 

 possible, while the remoter parts of the oceans have been left untouched. In many 

 cases, however, phenomena occurring in these areas are important for a correct 

 scientific assessment and the comprehension of ocean phenomena in general. A know- 

 ledge of conditions at the surface and beneath it covering the whole oceanic space is 

 necessary for the further development of oceanography. 



These considerations have led to the oceanographic expeditions that have contri- 

 buted so much to the science of the seas. The task of deep-sea expeditions is first and 

 foremost to determine the shape of the sea bottom and to measure as accurately as 

 possible the physical-chemical conditions of sea water between the bot tom and the 

 surface. Of major importance are the horizontal and vertical variations of the oceano- 

 graphic factors: temperature, salinity and dissolved gases. Variations in the first of 

 these indicate the variations in density and the latter ones allow a correlation with 

 marine biology which requires a knowledge of the environment of marine life. 



In addition to this more statistical knowledge of the physical-chemical structure of 

 the sea it is also desirable to know something about the circulation of water masses. It 

 is obvious that the internal circulation of the ocean must be related to the oceanic 

 structure. Because the driving force for the oceanic circulation lies partly in the 

 movement of the air over the ocean surface and partly in regional differences between 

 masses of water (or diff'erences of density of the masses) due to diff"erences in tem- 

 perature and salinity. If conditions in the oceans are steady there will be an inverse 

 relationship between the circulation and the thermo-haline structure. The earliest 

 method used to deduce the circulation system was based on such a correlation, using 

 an accurate survey of the thermo-haline structure. The determination of the move- 

 ments of water masses, the forces causing them and their seasonal variations in time as 

 well as local variations and transports are the main problem of modern oceanography. 



During the development of oceanography the character of oceanic expeditions has 

 undergone a transformation. The first expeditions were natura'ly only attempts to 

 clarify conditions and to overcome experimental difficulties on board the research 

 ships. The major deep-sea expeditions at the end of the nineteenth century and at the 

 beginning of the twentieth laid the foundations of modern oceanography. At first they 

 investigated only a section through the ocean, that is, along the route of the ship. 

 The results were based on discontinuous sampling and rarely reached to the sea bottom. 

 This method did not allow any three-dimensional conception of oceanic phenomena. 



Progress in oceanographic technique on board research vessels and modern de- 

 velopments in the recording and interpretation of results have made it possible since 

 the First World War to carry out systematic investigation of the ocean, not along one 



