values. Relatively little exchange takes place between the modified Circumpolar 

 Water and the Shelf Water it overrides as the intrusive layer extends southward 

 over the continental shelf. 



Westward of this cross section and entirely over the continental shelf (Fig. 

 7), further effects of the spreading modified Circumpolar Water and mixed Upper 

 Water are indicated. Modified Circumpolar Water rises to the south and mixes 

 with Antarctic Surface Water, forming a warm layer at Station B-08 where insola- 

 tion resulted in relatively high temperatures at the sea surface. 



Another series of stations occupied farther to the west but still in the central 

 Ross Sea (Fig . 6) demonstrates at Station B-08 the surface effect of the mixing of 

 Antarctic Surface Water and Circumpolar Water. Because of this mixing, surface 

 salinity values in this area are the highest in the Ross Sea. It is significant, too, 

 that the ice disappears earliest where this warmer-water mass has the greatest sur- 

 face expression (Figs. 18 and 19). This accounts for the previously unexplained 

 situation of the Ross Sea opening up "internally", with an ice-free area appearing 

 first in the west -central Ross Sea and growing asymmetrically outward as summer 

 progresses. Near bottom modified Circumpolar Water mixed with Shelf Water 

 merges to Shelf Water, as indicated by the several criteria. 



Offshore at Station E-05 (Fig. 7), Upper Water has mixed with Circumpolar 

 Water along their common boundary. As was mentioned earlier, little mixing has 

 taken place between Shelf Water and the warmer, less-saline Circumpolar Water. 

 The effects of mixing between adjacent layers are shown at Station B-10 (Fig. 20) 

 which is on the East-West and North-South cross sections in this area (Figs. 21 

 and 7). The profiles at Station B-10 indicate the Antarctic Surface Water extend- 

 ing from the surface to vestigial Winter Water at about 50 meters, which was ad- 

 mixed from below with modified Circumpolar Water. From about 80 to 200 meters, 

 modified Circumpolar Water exists with characteristic temperature-oxygen values. 

 A mixed zone extends downward from about 200 to 410 meters, with Winter Water 

 influencing and cooling the mass. The knees in the temperature and oxygen curves 

 and the changes in slope of the salinity and sigma-t curves provide evidence that 

 at about 480 meters pure Shelf Water was present, extending to bottom . 



The southern limit of modified Circumpolar Water extends to very near the 

 Ross Ice Shelf at Station B-07 (Figs. 22 and 6). Oxygen values present the strong- 

 est evidence, however, temperature, salinity, and sigma-t values also show, that 

 modified Circumpolar Water with a core at about 7b meters has influenced the 

 Antarctic Surface Water above it. A mixed layer with predominantly modified 

 Circumpolar Water extends from 80 to about 200 meters, mixing below this level 

 with Shelf Water. Effects of modified Circumpolar Water are not apparent below 

 about 300 meters . 



26 



