Introduction xv 



or two sections but using a narrow spaced net-work of stations over the whole of a 

 water mass from the surface to the sea bottom. This was the logical development of the 

 first voyages of research ships progressing from straightforward discovery to system- 

 atic exploration of a whole ocean along a carefully prepared plan. After some minor 

 research voyages of this type by Norwegian oceanographers came the first major 

 expedition for the systematic survey of a whole ocean, the German Atlantic Expedition 

 of the "Meteor" 1925-7 (Defant, 1928). 



Large expeditions such as this that give a deeper insight into the geographic variation 

 of the oceanographic factors over the entire ocean are essential for an extensive view 

 of the phenomena occurring in the oceans. The closer the network of stations the more 

 accurate such a survey will be, but the establishment of the closest possible network is 

 capable of only partial fulfilment. The work of the research ships can be intensified 

 only with difficulty to get a more rapid sequence of stations and there are difficulties 

 in the interpretation of the data recorded. The treatment of the results of a survey of 

 a whole ocean is based on the assumption that conditions in the ocean are steady. 

 However, this is only approximately true. Conditions in the water mass in an ocean 

 are on the whole quasi-stationary provided that they are not examined in too great 

 detail. Only in this case one is justified in concluding that the movements of water 

 masses from the thermo-haline structure, and the results of all the major ocean 

 surveys that have been made, have shown that this correlation of the physical- 

 chemical conditions can be relied upon for the general interpretation of the prevailing 

 currents in the ocean. This, however, gives a view of average conditions only. The 

 dynamics of the processes in detail are more complicated, as the somewhat rough idea 

 of the widely spaced network of oceanographic stations shows. 



This, together with more recent theoretical considerations, has led to the conclusion 

 that a closer study of the dynamics of the currents in the ocean cannot be based on the 

 observations of a rather wide-spaced network of oceanographic stations. It will re- 

 quire closely knit, preferable synoptic observations which can be obtained only by 

 collaboration between several research ships. Apart from these more specialized 

 surveys of oceanographic problems the older type of oceanographic survey remains 

 indispensable, although modern oceanographic research will change to an increasingly 

 synoptic concept of oceanographic phenomena. The last international joint survey in 

 the Gulf Stream area north of the Azores during the early summer of 1938 (Defant 

 and Helland-Hansen, 1939) marked the beginning of this type of joint investigation. 

 Probably the largest synoptic oceanographic survey has been the Operation Cabot of 

 the U.S. Hydrographic Office, 6-23 June 1950, which investigated the Gulf Stream 

 area between Cape Hatteras and the Grand Banks of Newfoundland using six ships 

 (FuGLiSTER and Worthington, 1951). 



This book is concerned with physical oceanography. It describes the three-dimen- 

 sional structure and movements, material and energy characteristics of the hydro- 

 sphere. Furthermore, the physical and chemical properties of sea-water, the regional 

 variations in the oceanographic factors and their periodic variations are dealt with. 

 It also describes the different types of ocean currents (ocean dynamics), and finally 

 the periodic movements of the water in waves, tides and related phenomena (dynamics 



