614 



The Tropospheric Circulation 



about 26-4 million m^sec. The transport in the current core has thus grown to twice 

 its magnitude in a distance of about 600 nautical miles. This very large increase from 

 26 to 83 million m^sec, where the current passes into a region with larger depth, can 

 be attributed to three principal sources. The smallest of these is due to the Antilles 

 Current which brings the total transport up to 37-1 million m^sec leaving 45 million 

 to be accounted for from the other sources. This is supplied, on the one hand, by water 

 drawn in from the south-western part of the Sargasso Sea and on the other hand, by 

 water fed by the counter current coming from the area of the Newfoundland Banks 

 and mixed with the Gulf Stream by means of numerous vortices. In this way Iselin 

 derived the schematic outline of the main sources and of the course of the Gulf Stream 

 shown in Fig. 286. Each line represents a water transport of about 12 million m^sec. 

 This may seem somewhat schematic, however, it gives an instructive idea about the 

 origin and composition of the water masses transported by the Gulf Stream. 



80° 70 60 50 4 



20 10° W 



Fig. 286. Schematic representation of the main sources of the Gulf Stream waters (broken 

 lines) and the pattern of the Gulf Stream system (continuous lines). In the western half of the 

 ocean each stream line represents a water transport of approximately 12 x 10® m^ sec~^ 



(according to Iselin, 1935). 



The systematic survey of the Gulf Stream between Montauk Point and the Bermudas 

 carried out by the "Atlantis" from June 1937 (Iselin, 1940) showed that the mass 

 transport of the Gulf Stream varied between 93 and 76 million m^sec. There was a 

 definite annual variation with two maxima in early summer and in winter and two 

 minima in October-November and April-May. The differences in the sea-level across 

 the current are closely related to these variations and can be deduced from them. 

 This annual variation is probably due to variations in the intensity of the atmospheric 



