INTRODUCTION 5 



Continent, as is generally supposed, but only in the south-western and western parts of 

 the Weddell Sea. From this region it spreads towards the east, and although it is con- 

 tinually mixing with the deep water and spreading towards the north it is not reinforced 

 by any appreciable addition of cold surface or shelf water. Its temperature and salinity 

 increase continuously towards the east from the Weddell Sea through the Indian and 

 Pacific Oceans to the west coast of Graham Land, and it thus follows that there is a very 

 sharp difference in the character of the water on the two sides of this promontory. The 

 oxygen content of the bottom water shows a continuous decrease along the same path. 

 A small part of the bottom water is formed between the South Orkney Islands and the 

 South Shetland Islands in the same way as the Arctic bottom water south of Greenland 

 and north and south of Jan Mayen (Nansen, 1912), by a convection which reaches from 

 the surface to the bottom in winter ; the greater part is, however, formed by the sinking 

 of highly saline shelf water in the south-western part of the Weddell Sea. 



New information has also been obtained as to the nature of the subtropical con- 

 vergence, which appears to be formed as a result of the balance between a northward 

 movement in the sub-Antarctic water and a southward movement in the subtropical 

 water. Its position has been found, in some parts of the ocean at least, to be subject to 

 much greater variations than that of the Antarctic convergence ; it advances towards the 

 south in summer, recedes to the north in winter, and in the central part of the Atlantic 

 Ocean it has other irregular movements with a range of as much as 6° of latitude. It has 

 also been found that the convergence is not necessarily the boundary between the 

 easterly current caused by the west winds of the forties and the westerly current caused 

 by the trade winds farther north ; it lies within the region of westerly winds, and the 

 water in the southern part of the subtropical zone generally flows eastwards. 



It is clearly recognized that much of the value of this report lies in the vertical sections 

 at the end of it, but it was thought unnecessary to describe the temperature and salinity 

 distribution in each section in detail, since the diagrams themselves are the best way of 

 giving this information. The lines along which the observations were made are shown 

 in Plate I. As many of the actual observations are reproduced in the diagrams as could 

 be included without causing confusion, but most of the data from the first 400 m. have 

 had to be left out. The data collected from the depths of o, 10, 20, 30, 40, 50, 60, 80, 

 100, 150, 200, 300, and 400 m. were, however, used in the production of the original 

 drawings, which are twice the size of the finished plates. The clearness of the diagrams 

 is largely the result of the careful work of Miss E. C. Humphreys, who prepared my 

 drawings for reproduction. 



Whilst I have endeavoured in writing this report to make suitable acknowledgment 

 of my indebtedness to the earlier workers on the subject, it is almost impossible to do 

 them complete justice. In the relatively short time at my disposal I have not been able 

 to read carefully through all the original reports and papers which have been published, 

 but have only been able to make short abstracts and have had to confine my attention 

 principally to the excellent summary accounts given by Schott (1926), Defant (1928), 

 Wiist (1928, 1929), and Moller (1929). It is most unfortunate that, having to complete 



