TEMPERATURE OF THE SURFACE WATERS OF THE ATLANTIC OCEAN 



15 



and density. Although both the temperature distri- 

 bution and the polar front in this area are subject to 

 sharp seasonal changes of position, the water move- 

 ment may, at least in principle, maintain its course 

 during the whole year according to the arrangement 

 shown in figure 17. 



The second boundary A' likewise arises from the 

 combined fronts between the Cold Wall and the Gulf 

 Stream. First it goes north, then turns east at about 

 51° N., where it can be recognized on the average as far 

 as 25° W. on the temperature gradients of 1.0° C. per 

 degree of latitude. These gradients are still steep in 



divides the temperate from the subtropical water. At 

 45° N. it runs as far as 30° W. Thence the cun-ent 

 streams and isotherms diverge so sharply that in the 

 eastern part of the ocean this boundary can no longer 

 be recognized. Current charts of O. H. Felber^' give 

 information on its origin. It is obviously connected 

 with the Gulf Stream and is located where the stream 

 lines on its left flank turn off on the north and in so 

 doing decrease both in stability and in velocity, and in 

 velocity especially. In other words, it designates the 

 northern boundary of the axis of the Gulf Stream. 

 Its seasonal fluctuations are greater than in A' and 



' = Polar front on basis of temperature distribution 



^ ^ _ As^Aw = Polar front in summer and winter 

 ^^,^_^_ A = Secondary polar front (Labrador front) 



V = Convergence area based on current displacements. 



X =A point plotted from temperature gradient profile, 



X =A point which could not be established for every month. 



T" "?" "P tB =Subtropical boundary 



FiGTjRB 16. — Average position of the fronts and boundaries in the North Atlantic Ocean, 



proportion to the environment. This second boundary 

 is to be interpreted as a secondary front within the 

 temperature zone, analogous to the boundary A' in 

 the south.^' Figure 17 shows that on this front 

 Atlantic water and water from the Labrador Current 

 meet at 50° to 52° N.; the condition here may be 

 a matter of a pure convergence. The front comes 

 to an end east of 25° W. by a mingling of the two kinds 

 of water. 



The third boundary, the subtropical boundary B, 

 can be distinguished from the group of fronts and 



reveal a displacement toward the north during the 

 summer. The boundary moves from 43° N. in January 

 to as far as 47° N. in August. The individual values are 

 not so widely scattered as in the south, because at this 

 point the boundary lies in the steamship path and a 

 great many observations are possible. This movement 

 of the boundary, therefore, seems to possess a certain 

 amount of reality. 



Finally, the area of the subtropical convergence can be 



'» Of. footnote 35. 

 " C(. footnote 34. 



