150 feet; consequently at a depth of from 200 to 300 feet there 

 remains a cold layer of winter-cooled water. The bottom of 

 this relatively cold layer sometimes extends to a depth of 

 500 feet or more. 



In the Ross Sea, and in other areas near the continental 

 fringe, the ice cover restricts surface heating. Local areas 

 will be alternately free of ice and then covered by floes. 

 This phenomenon results in very irregular thermal structures 

 in the surface layer. Very frequently, slight positive gradients 

 (i.e., temperature increasing with depth) exist in the upper 

 layers both in and near the ice. 



The processes by which these temperature structures are 

 developed are shown schematically in figure 4. Figure 4A 

 represents a block of Antarctic Ocean some distance from the 

 Antarctic Continent, as it would appear during the winter 

 season. The heavy curve represents the vertical temperature 

 structure with increasing temperature to the right. The tem- 

 perature, in the upper isothermal layer is very close to 

 -1 degree C. (30 degrees F.), increasing below 300 feet to 

 2.5 degrees C. (36 degrees F.) in the deeper circumpolar 

 water. This type of thermal structure is designated here 

 as W-l. 



A similar schematic block of ocean (shown in fig. 4B) 

 represents a change from winter to summer thermal struc- 

 ture. Here the heavy curve, representing vertical thermal 

 structure, differs from the winter curve only in the upper 

 150 feet. In this layer the heating has increased the temper- 

 ature to approximately 2 degrees C. (36 degrees F.). This 

 type of vertical thermal structure, designated here as S-l, 

 consists of a layer of cold water that lies between a negative 

 temperature gradient layer and a deeper positive gradient. 



:::MI:iM^I^.;:^jv^^ 





TYPE W 



and in the Ross Sea, winter 



cooling extends to great depths 



YPE S-,2, Early summer radiation 

 eats up the surface layer slightly. 

 Mechanical mixing by winds 

 extends, this layer downward. 



TYPE S-3, Melting ice flo< 

 set free from the .pack ne 

 may drift 'into the area 

 a positive gradient in th 

 upper layers. 



prodi 



11 



