NOTE ON THE DYNAMICS OF THE 

 SOUTHERN OCEAN 



By G. E. R. Deacon, B.Sc. 

 (Text-figs. 1-4) 



INTRODUCTION 



ON E of the most important tasks undertaken in the course of the extensive researches 

 which the Discovery Committee has been conducting into the hydrological and 

 biological conditions in the Southern Ocean is to find how the plankton distribution in 

 the sea depends on the water movements, and although much knowledge has already 

 been gained, many aspects of the problem — chiefly those concerned with the speeds of 

 the water and plankton movements — cannot be settled until a more trustworthy 

 representation of the water movements has been obtained. 



After a long examination of the hydrological data, mostly obtained from the Falkland 

 Sector, it seemed almost certain that the method generally employed — the application 

 of Bjerknes' theorem of oceanic circulation, in its specialized form, to the density and 

 pressure distribution — did not give such reliable results in the Southern Ocean as it 

 does in other parts of the world. 



Where the theorem can be relied on implicitly the movement in the neighbourhood 

 of each isobaric surface conforms to the dynamical topography of the surface and follows 

 the isobaths, but the accumulated data from the Falkland Sector pointed to the existence 

 of relatively strong movements across the isobaths ; the warm deep current, for example, 

 seems to have a stronger southward trend. Although it must be admitted that the 

 counter evidence was not unquestionable, there was a strong indication that the topo- 

 graphical charts did not give an accurate representation of the current system. 



With the problem at this stage the results obtained during the circumpolar cruise 

 made by the R.R.S. 'Discovery II' in 1932-3 presented a unique opportunity for 

 testing the usefulness of the charts on a wider scale, and for the first time charts could 

 be drawn to show the relative topographies of the isobaric surfaces round the whole of 

 the Southern Ocean. Charts showing the topographies of the o and 600 decibar surfaces 

 relative to the 3000 surface are given in this report, and a comparison of the conclusions 

 that can be drawn from them with others drawn from a more general treatment of the 

 temperature and salinity data (Deacon, 1937) also indicates that the specialized form of 

 Bjerknes' theorem does not give a true picture of the currents. 



In the hope that the problem would interest more skilful workers the complete data- 

 anomalies of specific volume and dynamic depth— for 113 stations in the Southern 

 Ocean are given in Tables at the end of this report. In order to make the report more 

 complete it was thought useful to begin it with a brief indication of the method by which 

 Bjerknes' theorem has been developed; the method is taken chiefly from a paper pub- 

 lished by Sandstrom and Helland-Hansen in 1903. 



