values. A temporary subsurface layer of increased temperatures may be 

 formed just below the sea surface by summer warming and followed by cool- 

 ing of the sea surface. This layer can be differentiated from Antarctic 

 Circumpolar Water by the low salinity and high oxygen values. 



The thickness of Antarctic Circumpolar Water generally decreases in 

 the direction of movement. Seaward of the continental slope, this water 

 mass is about 2,000 meters (6,562 feet) thick. Within the Ross Sea, its 

 thickness is only about 150 to 250 meters (492 to 820 feet), becoming 

 less than 100 meters (32 8 feet) along the Victoria Land coast. 



It was observed that Antarctic Circumpolar Water penetrates mainly 

 the area occupied by Winter Water (Figs. 6-10). Shelf Water appears to 

 be dense enough to act as a barrier to any extensive penetration by 

 Antarctic Circumpolar Water (Fig. 8). Where Shelf Water is plentiful, 

 little or no Antarctic Circumpolar Water can intrude. The data collected 

 during DEEP FREEZE 64, for example, showed little or no Shelf Water pres- 

 ent in the eastern Ross Sea; and circumpolar water influence was observed 

 at all stations. 



Figure 16 schematically illustrates the pattern of the Antarctic 

 Circumpolar Water intrusion, including the subsurface temperature maxima 

 and depths at which these maxima occurred. One of the areas of strongest 

 intrusion is along the boundary of the 1963 and 1964 operating areas. 

 An attempt has been made to correlate data taken on DEEP FREEZE Operations 

 63 and 64; however, it was observed that continuity between the two years 

 did not exist due to unstable summer conditions. 



The general vicinity of Antarctic Circumpolar Water entry into the 

 Ross Sea, appears to be north of 75°30'S between 176°W and 180°. The lack 

 of data from this area limits the analysis of intrusion of Antarctic 

 Circumpolar Water. 



It appears that the main intrusion moves up the continental slope and 

 enters near the central part of the Ross Sea. This intrusion branches 

 into southward and westward moving components, influencing much of the 

 southwestern Ross Sea. In the vicinity of stations 72, 75, 78, 81, and 

 83, Antarctic Circumpolar Water is forced near the surface by the under- 

 lying Shelf Water and mixes with the Antarctic Surface Water (Figs. 17 

 and 18). This area of mixing becomes warmer as a result of circumpolar 

 water influence, and this is the area which becomes ice-free first in the 

 austral spring (U.S. Navy Hydrographic Office, 1961). 



Additional intrusions of circumpolar water enter the western Ross Sea 

 from the north between Pennell Bank and Victoria Land. These intrusions 

 mainly affect the northwestern part of the Ross Sea. 



In the eastern Ross Sea, it was observed that the main intrusion of 

 Antarctic Circumpolar Water enters near Cape Colbeck. This intrusion 

 penetrates throughout the eastern Ross Sea, in varying degrees, influ- 

 encing all stations taken during DEEP FREEZE 64. 



23 



