294 DEACON [CHAP. 12 



deep water and, in the Antarctic zone, the highest phosphate and nitrate 

 concentrations are found in the "warm deep layer. Silicate is most abundant in 

 the bottom water, as though most of it were regenerated from the solution of 

 the skeletons of diatoms near the bottom. There is generally a very sharp fall 

 in silicate from south to north across the Antarctic convergence. 



Further study of the patterns of phosphate and silicate distribution is likely 

 to give useful indications about the history and circulation of the water- masses, 

 but there appear to be large fluctuations with variations in growth and 

 mortality, and many more observations are needed. 



7. Future Needs 



Kidson (1932), discussing the problems of Antarctic meteorology, said that 

 the predominance of ocean- over land-surface in the Southern Hemisphere 

 renders the mechanism of the general circulation simpler and more regular 

 than in the Northern, and added that it should, therefore, be possible to arrive 

 at sound generalizations from fewer data. This is undoubtedly true, but the 

 theoretical treatment of the circulation nevertheless seems to present at least 

 as much difficulty as the other oceans. If treated as a purely zonal current 

 driven by the prevailing west wind, its velocity becomes much too large unless 

 restricted by large arbitrary eddy viscosities which seem out of keeping with 

 persistence of well defined deep and bottom layers, and warm and cold surface 

 and sub-surface strata. Proudman (1952, p. 190) shows that this difficulty is 

 removed as soon as we allow appreciable meridional movements in the different 

 layers and take account of accelerations relative to the earth as they move 

 towards higher and lower latitudes. Stommel (1958) also shows that better 

 agreement with observations is obtained when we recognize that it is not a 

 zonal current after all. Assuming restriction of the zonal movement by South 

 America, Graham Land and the connecting submarine arc, he sets up theoretical 

 models which face the difficulty of assuming a net meridional flow and produce 

 a dynamic topography with striking resemblances to the observed pattern. 



Current measurements at all depths are urgently needed, but many must be 

 made, with as much guidance as possible from theoretical models, before much 

 advance can be made. It is reasonable to expect considerable seasonal changes 

 in transport : more Antarctic bottom water is likely to be formed in winter, 

 and there is probably a greater northward flow of Antarctic surface water in 

 summer when ice is melting. The southward flow in the deep layer must be 

 affected by changes in both layers. It would be very useful if natural radio- 

 active tracers, such as 14 C, could be used, but their interpretation will be 

 uncertain till there is a better background of physical measurements. 



It is difficult to emphasize the need for new work without some risk of 

 appearing to underestimate the value of what is being done. Some of the new 

 oceanographical techniques, such as underwater photography, bottom corers, 

 greatly improved echo-sounders and seismic methods, are being put to good 

 use, but very few deep temperature and salinity observations and no current 



