The changes in thermal structure that take place near 

 the Antarctic Continent differ somewhat from those further 

 north. Figure 4C represents, schematically, a block of ocean 

 near the continent or in the Ross Sea and the corresponding 

 winter temperature structure. The more intense cooling 

 results in a cold isothermal layer extending to a greater 

 depth here than in the northern region. This type of temper- 

 ature structure is designated here as W-2. 



Summer heating in the higher latitudes is less pronounced; 

 however, it extends to greater depths because of greater wind 

 mixing (see fig. 4D). A further alteration of this summer 

 thermal structure may result when ice. is blown either into 

 or close to this area. This must frequently be the case as 

 the ice pack is always present around the continent. In summer 

 large pieces that break off the pack will drift into nearby 

 areas which had previously been made ice-free by the radiation 

 surplus. These melting bergs or ice floes cool the surface 

 layer; thus a positive gradient is produced near the surface. 

 Since this melted ice has a low salinity, the positive gradient 

 remains fairly stable. The resulting thermal structure then 

 consists of a warm layer between approximately 100 and 

 300 feet, with a positive gradient above and a negative gradi- 

 ent below (see fig. 4E). These last two summer types of 

 structure are designated here as S-2 and S-3, respectively. 



Typical BT Traces . Individual bathythermograph traces 

 showing typical temperature structures obtained in the ant- 

 arctic and their distribution are shown in figures 5 through 10. 

 These areas frequently overlap, and due to local conditions, 

 the thermal structure typical of one particular area may occur 

 in other areas in which a different characteristic structure 

 predominates. Thermal structure of the type W-l typifies 

 the usual antarctic surface thermal structure before surface 

 heating has created the upper negative temperature gradient 

 (see fig. 5). This type of structure was observed north of 

 70°S in ice-free areas only early in the summer season 

 (December). This same structure was often found in the 

 neighborhood of the ice floes at the entrance to the Ross Sea 

 throughout the summer season. Type S-l, shown in figure 6, 

 represents the most typical summer thermal structure, with 

 the summer-heated surface layer extending to about 150 feet 

 and the residual, winter-cooled, minimum temperature layer 

 extending to 300 and sometimes 500 feet; below this there is 

 the transition layer with increasing temperatures with depth. 



12 



