44 DISCOVERY REPORTS 



decreases towards the north, and the northern part of the Antarctic Zone appears as a 

 belt of minimum salinity between this water and the more saline water in the sub- 

 Antarctic Zone. 



The salinity in the southern part of the zone in winter varies from 34-0 to 34-5 °/ 00 , 

 being greatest in the Weddell Sea. Where there is a strong northward movement, such 

 as in the Weddell Sea, near the Kerguelen-Gaussberg ridge, near the Balleny Islands, 

 near the Cape Adare-Easter Island ridge and near Peter 1st Island, the region of high 

 salinity extends farther north. In the northern part of the zone the salinity is greatest in 

 these localities, but nowhere does it fall below 33-8 °/ 00 . The approximate positions 

 of the 34-0 °/ 00 isohalines are shown in Fig. 1 1, the greater part of which shows the con- 

 ditions in winter ; the chart is, however, based on rather scanty data and at present the 

 distribution is partly hypothetical. 



In summer the salinity of the Antarctic water is much more varied, the surface 

 stratum has generally a much lower salinity than the cold stratum, and there are also 

 greater horizontal changes. At the surface the lowest salinity is found near the pack-ice 

 or land ; in such regions it is frequently lower than 33-0 °/ 00 , and there is little doubt that 

 if the water were just scooped from the surface near to drifting ice it would be much less. 

 Farther north the poorly saline water is more evenly mixed into the main body of the 

 layer ; the salinity at the surface is therefore greater than it is near to the pack-ice, but the 

 salinity of the cold stratum is less ; owing to more addition from melting ice as the current 

 flows northwards, that of the layer as a whole is also less. In Fig. 7 (p. 27), which shows 

 the average salinity of the first 100 m. of water in the Falkland Sector in early summer, 

 there is a belt of minimum salinity just south of the convergence. There is probably 

 such a belt of low salinity round the whole of the Southern Ocean, but there are as yet 

 insufficient data from the summer months to allow a chart to be drawn. 



The temperature and salinity of the Antarctic surface water are subject to large 

 seasonal and annual changes ; they have been closely examined in the neighbourhood of 

 South Georgia and will be the subject of a separate report. The mean temperature and 

 salinity of the first 50 m. of water have been found for the region between 52-56 S and 

 33-41 W. Between 1925 and 1933 the mean temperature of this area in January varied 

 between 0-63 and 2-43° C, and the salinity between 33-64 and 33-97 °/ 00 . The seasonal 

 change of temperature from winter to summer seems to be usually about 4 C. ; the 

 change of salinity is not so regular and depends very much on the amount of the annual 

 change. In the years 1928-9, for instance, the salinity of the area investigated increased 

 from 33-60 to 33-82 °/ 00 from summer to winter, but only decreased to 33-78 °/ o0 during 

 the following summer. The fewer observations made near the Antarctic convergence 

 indicate that the seasonal change of temperature is slightly smaller there, whilst the 

 seasonal salinity change is greater. 



