48 



Hydrography op the Stream 



obtained, and the cross-current pressure gradients calculated. 

 Also, because of the large eddies found both north and south of 

 the Stream, any section made across the area must be long enough 

 to ascertain whether or not more than one pronounced pressure 

 gradient exists. If only one is found it defines the Gulf Stream, 

 but if more than one are located then the position of the Stream 

 cannot be determined by that single section. 



33 4 5 6 



4000 



4500 



Fig. 23. Salinity section across the Gulf Stream, Chesapeake Bay to 

 Bermuda, February 11-18, 1932, according to Iselin (1936, fig. 4). 



Not to be confused with the inner or left-hand edge of the 

 Stream is the temperature -salinity boundary at the surface. This 

 generally abrupt change that occurs to the left of the ' warm core ' 

 may or may not coincide with the left-hand edge of the Gulf 

 Stream as defined above. This appHes also to the color boundary 

 and the long thick lines of Sargassum frequently seen on the 

 surface ; all of these surface phenomena are apparently associated 

 with shear zones to the left of the ' warm core ' but they are not 



