18. 



TEMPERATURE OF THE SURFACE "WATERS OF THE ATLANTIC OCEAN 



and 20, which reveal these changes in position in the 

 one-degree bands 30° W. to 31° W. and 20° W. to 21° 

 W. in the form of isopleth diagrams ^* of the tempera- 

 tm^e. In the case of the eastern band, the maximum 

 hes at 15° N. in September, simultaneously with the 

 appearance of the temperature maximum of 28° C. 

 The most southerly position is reached in April at 0° 

 latitude with the second temperatm'e maximum at 

 28.0° C. In the western band (30° W. to 31° W.) the 

 fluctuations are greater; here the thermal equator 

 swings back and forth between 10° N. in September 

 and 10° S. in February. The double temperature 



relationships provide the explanation for this extension 

 into the South Atlantic Ocean. In fact, just as is shown 

 by the current displacements in the Dutch atlases, a 

 pronounced current moves southwest between 25° W. 

 and 30° W. precisely in the doubtful months and 

 transports the warm water of the south equatorial cur- 

 rent in this direction. As an example, figure 21 shows 

 the position in April. It is clear that the deviation of 

 the current, drawn according to the Dutch two-degree 

 field values, sets in to the southeast toward the BrazU 

 Current even at the equator; that is, considerably more 

 to the north. On the current chart for February by 



Figure 19. — Thermoisopleths on the surface for the one-degree field bands 30° W. to 31° W. between 15° N. 

 and 13° S., with the position of the thermal equator. 



maximum, which will be discussed later in more detail 

 in the treatment of the annual course of the tempera- 

 ture, also occurs here, with one maximum of 27.9° C. 

 in September and a second one of 27.6° C. in April. 



Although it has never before been mentioned in the 

 literature on oceanography, there can no longer by any 

 doubt of the strildng phenomenon of the extension of 

 the zone of highest water temperature to the southern 

 hemisphere in the months February, March, and April, 

 with the maximum occurring in April. The current 



3B The differences in the data for latitude for the thermal equator in the isopleth 

 illustrations and on the chart lie in the fact that in figures 19 and 20 the interpolation 

 had to be carried out linearly, and on the chart (fig. 18) according to surface 

 (flSchcnhaft). 



Meyer, this southern component of the water action 

 at this point is only weakly expressed. 



The maximum extension of the tropical zone in the 

 Atlantic can, therefore, be limited by means of the 

 average northern and southern extreme position of the 

 thermal equator in the surface water DD', as shown 

 in figure 18. 



The average position of the thermal equator, as 

 obtained from the annual temperature averages of the 

 two-degree fields is a hne running from Cape Gracias a 

 Dios through the Caribbean Sea, north of Jamaica, to 

 Martinique, south to about 5° N., and across that 

 parallel to Cape Palamas and Fernando Poo. In table 



