60 Hydrography of the Stream 



in two dififerent ways. The essential decision to make in interpretation is 

 whether there is an isolated central core or whether there is a tongue con- 

 nected to the lower fluid. If the chart is regarded as a vertical temperature 

 section the likehest interpretation is that there is no connection and that 

 the cold central mass is fresher; hence, there would be no violation of 

 vertical stability. There is no proof, however, that the water cannot be 

 momentarily unstable (from intense turbulence, the breaking of internal 

 waves, etc.), and hence the alternative interpretation is not automatically 

 ruled out. Simultaneous salinity measurements help to settle the issue, but 

 they are not usually available in bathythermograph sections. Such tem- 

 perature inversions are common in the side of the Stream toward the coast 

 and have been discussed by Ford, Longard, and Banks (1952), who find 

 them frequently made up of freshened water (30-5-34-5%o as opposed to 

 36-5 %o in the Sargasso water in the central North Atlantic). 



Similar ambiguities of contouring arise in drawing horizontal charts, and 

 these ambiguities are likely to be even more perplexing because the Hnes 

 of data on the chart are fewer. It is often impossible to decide whether to 

 draw a stream with an eddy to one side or the other, a sharp S-shaped 

 curve in a single stream, or three separate streams. The only successful and 

 practical way to resolve this difficulty is to meet it at the time when it 

 arises, by proper planning on board the survey vessel. This is a good 

 example to demonstrate why cruises cannot be entirely planned ahead of 

 time and why the uncomfortable job of taking oceanographic data cannot 

 be left entirely to untrained personnel. 



THE STRATEGY OF EXPLORATION 



In the present state of physical oceanography most of the effort must be 

 devoted to field work, in an attempt to explore and describe the chief 

 physical features of oceanic phenomena such as the Gulf Stream. This does 

 not mean that theoretical studies are not worth while, but it does mean 

 that the chief features are so poorly known that a serious theoretical 

 analysis of the Gulf Stream cannot be made at present. We have seen how 

 the oceanographic surveys of the 1930's have given a broad, general view 

 of the ocean surface circulation and have delineated the major, average 

 thermal and salinity structure of the waters. These early surveys are all 

 characterized by a common strategic practice : the courses and spacing of 

 stations were planned in advance; and the sections actually made corres- 

 ponded as closely to these preliminary plans as the exigencies of current 

 set, weather, and instrumental failure would permit. The early Meteor 

 studies of the South Atlantic, the present-day West Coast survey, and the 

 first ten years of Atlantis cruises in the Gulf Stream, are all examples of 



