In the antarctic region, however, relatively large temper- 

 ature gradients occur at depths greater than the depth to which 

 the bathythermograph will reach. The character of the surface 

 traces are related to these deeper phenomena; thus the dis- 

 cussion of the surface layer thermal structure must neces- 

 sarily include general consideration of the character of the 

 deeper waters. 



General Character of the Thermal Structure. In the winter 

 (June, July, and August) during a period of active cooling, the 

 antarctic region is covered with a surface layer of nearly 

 homogeneous water. In the southern half of the region this 

 water is near freezing (lower than -1 degree C), but further 

 north the temperature rises to +1 degree C. and, at the Ant- 

 arctic Convergence, the northern boundary of the antarctic 

 region, the temperature increases very abruptly. 



Below this isothermal layer, which extends about 300 feet 

 below the surface, there is a transition region in which the 

 temperature increases with depth. This transition layer lies 

 between the surface layer and the antarctic circumpolar water. 

 The antarctic circumpolar water, a very large, well-defined 

 water mass, is characterized by a temperature maximum of 

 slightly above 2 degrees C. at a depth of between 1500 and 

 2000 feet. These conditions exist all around the Antarctic 

 Continent. 



In summer, during the period of increased radiation 

 surplus, the heat is first used mainly to melt the ice. Later, 

 some of this radiation surplus is used to heat the surface 

 layers. The temperature increase seldom extends below 



FIGURE 4. Schematic representa- 

 tion of the development of temper- 

 ature gradients in the antarctic. 



TYPE W-l. The upper 300-500 feet 

 is cooled nearly to freezing tem- 

 peratures. Relatively warm antarctic 

 circumpolar water at depths 

 greater than 500 feet produce a 

 positive gradient below the 

 winter-cooled layer. 



TYPE S-l. Summer heafing of 

 Type W-1 in the upper 150 feet 

 produces this most typical 

 antarctic summer thermal structure 



10 



