boundary. Soon after crossing it, observers on the HENDER- 

 SON encountered their first group of icebergs. As the con- 

 vergence was crossed, the water changed in color from blue 

 to gray, new types of birds appeared, and the sky cleared. 

 These changes closely followed the drop in temperature which 

 was over 2.5 degrees C. in about 20 miles. 



Location of the Convergence. As an aid in locating the 

 Antarctic Convergence, as well as presenting the complexities 

 of the antarctic thermal structure, horizontal temperature 

 plots and vertical cross sections of temperature versus 

 depth have been constructed for five locations as shown on 

 the chart in figure 12. They are numbered A, B, C-l, C-2, 

 and C-3 for reference. 



Both the plots and cross sections are based on a series 

 of bathythermograph observations taken by individual ships 

 on nearly straight runs across the convergence. Three of 

 the sections, C-l, C-2, and C-3 were taken in the same lo- 

 cality and serve to indicate the seasonal trends in the location 

 of the convergence. These features are discussed more 

 fully below. 



Horizontal Surface Temperature Sections . Ideally, if the 

 surface temperatures were plotted against latitude, with 

 temperature as the vertical coordinate and latitude as the 

 horizontal coordinate, the Antarctic Convergence should 

 appear on such a plot as a sharp break in the slope of the 

 surface temperature curve. A schematic presentation of 

 such a graph under ideal conditions is shown in figure 13. 



FIGURE 13. Schematic representation of 

 sea surface temperature section across 

 the Antarctic Convergence. 



26 



