TEMPEEATURE OF THE SURFACE WATERS OF THE ATLANTIC OCEAN 



13 



the current displacements, do not reach large amounts. 

 Table 5 gives information on these fluctuations at 

 30° W. and 20° E. 



The only exception to this fluctuation is the area 

 immediately off the Brazilian coast. Here the front 

 is displaced from the mouth of La Plata in the southern 

 summer to a point almost as far as 25° S. in the southern 

 winter. Because of these large movements, the bound- 

 aries in figure 4 are not carried out as far as the coast. 



A short summary of the fronts of the South Atlantic 

 Ocean is as follows: on the basis of the temperature dis- 

 tribution, two boundary zones can be established, the 



forms the dividing line between the west wind and the 

 subtropical areas, and is thus the pole-side boundary of 

 the subtropics. The subtropical convergence, on the 

 other hand, lies within the subtropics and forms no 

 pronounced "climatic boundary." Finally, the bound- 

 ary Ai' partly divides the belt of temperate water 

 masses of the west drift into a northern and a southern 

 zone. 



b. North Atlantic Ocean. 



Because of the complicated distribution of water and 

 land and the influence of the Gulf Stream, conditions 



Figure. 14 — Surface currents and temperature distribution in the area of the Falkland and Brazil currents in December. Designa- 

 tion of the fronts is the same as in figure 4. 



polar front and the subtropical boundary. The polar 

 front at about 50° S. corresponds to the dynamic 

 processes and is located where the so-called "interme- 

 diate water," which is, according to Defant and Wiist, 

 antarctic and subantarctic water, sinks below the 

 surface. The subtropical boundary at about 40° S. 

 coincides with the subtropical convergence only in 

 the western part of the ocean, where the Falldand 

 and Brazil Currents meet. This convergence, already 

 well-known from the currents, is located from 40° W. 

 to 10 degrees of latitude farther north. If the polar 

 front separates antarctic water from water of the west 

 wind drift, then, as can be deduced from the tempera- 

 tures established at the fronts, the subtropic boundary 



in the North Atlantic are not so simple as in the South 

 Atlantic. The most striking phenomenon in the north 

 is the band of extraordinarily steep temperature gradi- 

 ents of about 5° C. per degree of latitude off the North 

 American coast near Labrador (cf. plates V-XVII). It 

 extends on the average, for example, at 50° W., from 

 39° N. with a temperature of 21° to 44° N. at a tem- 

 perature of 6°, and thus separates subtropical water 

 from predominantly arctic. This strip, hemmed in on 

 the one hand by the Gulf Stream and on the other by 

 the so-caUed "Cold Wall," encloses the temperate zone, 

 which with its breadth of 5 degrees of latitude, is only 

 half as wide as the temperate zone of the South Atlantic. 

 Here also, as the current charts of P. M. van Kiel and 



