The Tropospheric Circulation 611 



edge is sharply defined and keeps about 100 km off the coast. The right-hand edge is 

 diffuse and differs little from the water farther to the east. Where it swings eastward 

 the current spreads out and loses thermal and haline thickness by mixing with colder 

 surrounding waters. To the south of the Newfoundland Banks it begins to break up 

 into a number of branches ; profile VI shows only the northern branch which borders 

 on the Labrador Current. The further branching of the current in the east has been 

 discussed on p. 562, Fig. 257. 



The Gulf Stream is only slightly more saline than the Sargasso Sea and in the 

 deep layers there is no difference. The salinity maximum lies in the subtropical 

 undercurrents which enter through the Antilles as part of the North and South 

 Equatorial Currents into the American Mediterranean and from there across the Gulf 

 of Mexico into the Florida Strait. It is thus a long-range effect of the tropospheric 

 circulation of the tropical and subtropical Atlantic. The Antilles Current also shows 

 this highly saline intermediate layer; but here it is in direct connection with the highly 

 saline top layer of the Sargasso Sea. Further along the course of the Gulf Stream this 

 salinity maximum comes at times up to the surface, but in the North Atlantic Current 

 it dips beneath the weakly saline surface layers. It can be traced well into the Norwegian 

 Sea (see pt. I, p. 171, Fig. 74). The salinity profile also shows another long-range effect 

 of the Atlantic circulation: this is the last traces of the weakly saline subantarctic 

 intermediate water which can still be seen at a depth of between 700 and 1000 m 

 {S < 34-9%o) as far north as 25° N. in the Florida Strait; in the Sargasso Sea, however, 

 it reaches only to 10° N. 



The dynamics and the water transport of the Gulf Stream are derived primarily 

 from velocity profiles. Several such profiles are available at the present time; they are 

 based partly on direct-current measurements and partly on dynamic calculations from 

 the mass field. The cross-section is not everywhere completely occupied by the current; 

 particularly where the current flows out of the Florida Strait into the open ocean. 

 The current flows as a jet through the narrow part of the strait and follows the direction 

 imposed on it for a considerable distance. The velocity distribution in the cross- 

 section is related to the mass field and the agreement between the calculated and 

 observed current profiles is generally good. Beyond the junction of the Florida 

 Current and the Antilles Current the weak counter current between them disappears 

 completely, but the counter current on the right-hand side of the main one is retained. 

 In the cross-section off Chesapeake Bay shown in Fig. 284 it lies just outside the 

 profile. 



A deeper insight into the dynamics of the current can be obtained from the absolute 

 topography of the isobaric surfaces and of the physical sea level. These are parti- 

 cularly dependent on the choice of the reference-level. In the narrows of the Florida 

 Strait this lies near the bottom where the velocity decreases almost to zero. Further 

 north it lies in the Sargasso Sea at about 1900 m depth (corresponding to Fig. 272) and 

 rises steeply from the right-hand side of the Gulf Stream to 1000 m depth or even less. 

 Over the current core the physical sea level rises steeply from left to right and at Cape 

 Hatteras this rise amounts to about 100 dyn cm. It remains more or less of the same 

 order up to the Newfoundland Banks, but gradually spreads out horizontally so that 

 the actual gradient falls to about a third. The right-hand side of the Gulf Stream is 

 associated with a high-pressure ridge which can be traced from the Bahamas to the 



