Antarctic Circumpolar Water is still recognizable throughout the Ross 

 Sea by its relatively high temperatures and increased salinities. Oxygen 

 minima also were used on previous oceanographic operations to identify 

 Antarctic Circumpolar Water; unfortunately, on DEEP FREEZE 63, all oxygen 

 values proved to be invalid because of malfunctioning equipment. 



3. Shelf Water, as identified in figure 4, is the coldest, most sa- 

 line, and most dense water mass in the Ross Sea. It is present mainly 

 in the southwestern part of the sea, and, where present, seems to act as 

 a dynamic barrier against Antarctic Circumpolar Water intrusion. 



Two cross sections presenting the generalized relationship of water 

 masses in the Ross Sea are shown in figures 5a and 5b. 



B. Antarctic Surface Water 



Antarctic Surface Water is a seasonal phenomenon derived from the 

 upper water in the Ross Sea. It is formed by melting of the ice cover 

 and subsequent dilution and warming of the water at the surface. Surface 

 water temperatures vary considerably, as do the salinity and thickness of 

 this layer (Figs. 6-10). These variations are caused by the nearness of 

 ice shelves (Fig. 11), presence of ice cover, time of the season (Figs. 

 12-15), and the characteristics of the underlying Winter Water or Shelf 

 Water. Antarctic Surface Water probably does not exist during the winter 

 season, as surface freezing increases the salinity and decreases the tem- 

 perature, causing a return to the characteristics of the underlying water. 



The Antarctic Surface Water layer lies over a Winter Water layer at 

 most stations. A noticeable temperature increase, part of the surface 

 water caused by summer warming, sometimes is present about 50 meters (164 

 feet) below the surface. Below this layer with higher temperatures, a 

 decrease in temperatures occurs representing the Winter Water layer (Figs. 

 8, 9, 12-15). At many of the stations, however, a definite boundary be- 

 tween the Antarctic Surface Water and underlying Winter Water is difficult 

 to define. 



The Antarctic Surface Water layer is thinnest along the western Ross 

 Sea. In the vicinity of Coulman Island and Lady Newnes Ice Shelf, depth 

 of the surface layer is only about 25 meters (82 feet). This surface layer 

 increases in thickness to about 100 meters (328 feet) near the center of 

 the Ross Sea. Generally, the Antarctic Surface Water grades into Winter 

 Water or Modified Winter Water; however, along the Victoria Land coast and 

 at the southwestern stations (Fig. 9), the Antarctic Surface Water grades 

 directly into Shelf Water with only a suggestion of the presence of Winter 

 Water. At other stations (Fig. 7), this surface water grades into Modified 

 Circumpolar Water. 



