136 DISCOVERY REPORTS 



southern part of the Atlantic Ocean shows very clearly that the least north or south 

 movement is to be found some distance above the bottom, in the stratum between the 

 southward flowing warm deep current and the northward flowing Antarctic bottom 

 current. The 3000 decibar surface lies rather low in this stratum and principally in the 

 northward bottom current, but since the general eastward movement may, unlike the 

 meridional movement, be weakest near the bottom it seemed advisable to use a surface 

 that was as deep as possible without being in the lowest stratum of the bottom current. 



The principal topographical feature of the o decibar surface is a downward slope from 

 north to south, the anomalies being highest in the north and lowest near the Antarctic 

 continent. The dynamic isobaths are not always parallel to the lines of latitude, but 

 although they bend successively towards the north and south in different localities their 

 resultant trend, except in the region north of the Weddell Sea, is slightly south of east. 

 If the 3000 decibar surface is level the surface current will have the same trend, but a 

 consideration of the distribution of temperature and salinity in the surface layer and the 

 few available current measurements and drift records fails to support this conclusion, 

 and although the current shows some dependence on the isobaths changing its direction 

 as they alter their course, its main trend appears to differ considerably from theirs. 



Where the isobaths bend towards the north the surface current generally has a strong 

 northward movement. Such movements occur north of the Weddell Sea, north-west 

 of the South Sandwich Islands, near the Kerguelen-Gaussberg Ridge, and in 150 W 

 near the Cape Adare-Easter Island Ridge. Where the isobaths bend southwards, in the 

 South Sandwich deep, between 30 E and 40 E, south of Australia, and in the eastern 

 part of the Pacific Ocean, the surface water has a weaker northward movement and it 

 may even have a small trend towards the south (Deacon, 1937, pp. 24-40). 



In the Southern Ocean as a whole, however, and not only in the region north of the 

 Weddell Sea, the surface current must have a northward trend. The low temperature 

 and salinity of the surface water in the Antarctic Zone and the low salinity of the surface 

 stratum in the sub-Antarctic Zone show that the surface current must be constantly 

 reinforced by a northward movement from the Antarctic region. It is, in fact, rather 

 doubtful whether the northward movement is completely interrupted even where the 

 isobaths bend sharply southwards : the hydrological conditions in these regions are not 

 very different from those found in the localities where the water is known to spread 

 strongly northwards, and they do not prove more than a weakening of the northward 

 movement. 



Owing to the relatively small number of current measurements that have been made 

 in the Southern Ocean there is still some disagreement between the current charts 

 based on them, but the charts given by the most recent workers, Meyer (1923) in the 

 Atlantic Ocean, Michaelis (1923) and Willimzik (1924) in the Indian Ocean, and 

 Merz (Wiist, 1929, p. 41) in the Pacific Ocean, all point to the existence of a northward 

 movement spreading from the Antarctic continent. The northward drift of icebergs and 

 drift-ice affords further evidence of such a movement. 



The bulk of the available evidence suggests therefore that the surface current has a 



