DEEP CURRENTS: ATLANTIC OCEAN 87 



Fig. 22 has been prepared showing the temperature distribution at the level of maximum 

 temperature. Since this level can only be distinguished clearly in the Antarctic Zone the 

 chart is confined to that region, and its use is therefore rather limited. In the sub- 

 Antarctic Zone, where the depth interval between the upper part of the layer and the 

 level of maximum salinity is greatest, and the movements in the two strata are most 

 likely to differ, the movements in the upper stratum cannot be examined by such a 

 simple method; they may, however, be determined with reasonable certainty by an 

 examination of the volume and properties of the stratum in the vertical sections. The 

 potential temperature of the water has not been used in Fig. 22 because the variation of 

 the depth of the level of maximum temperature is only small and the temperature cor- 

 rections to be applied for adiabatic changes are negligible. 



In each of the charts showing the properties of the deep layer, data collected during 

 one year or season have been combined with those of other seasons without making any 

 allowance for seasonal or annual changes. These changes are known to be such as cannot 

 be entirely disregarded, but where the observations made in different seasons have 

 fallen close together on the charts the changes have not been found large enough to alter 

 the general shape of the isotherms and isohalines. The changes are greater in a region 

 of steep temperature and salinity gradients than in another where the gradient is small, 

 but owing to the closeness of the iso-lines in such a region the seasonal change shows no 

 great displacement of any of them ; the average positions used in the charts are on the 

 whole trustworthy. The seasonal and annual changes of oxygen content were found to 

 be greater, and although they are not large enough to affect the general picture of the 

 distribution, the chart is not so accurate as the temperature and salinity charts. Although 

 the charts are in all probability reasonably accurate the possibility that the distributions 

 may be misrepresented by combining data from different years has been borne in mind. 

 Owing to the great reduction of the charts (from 21-5 x 17-5 in.) it has been found im- 

 possible to show all the data, but the points for which figures were available are indicated 



by dots. 



THE DEEP CURRENTS IN THE SOUTHERN PART OF 

 THE ATLANTIC OCEAN 



Merz and Wiist (1922) and Wiist (1928) have shown quite conclusively that the 

 highly saline deep water found in the Argentine Basin, south of the Rio Grande rise 

 and west of the mid-Atlantic ridge (see Plate XLIV), belongs to the North Atlantic 

 deep current, and is water which sinks from the surface in the subtropical region of 

 the North Atlantic Ocean. The distance to which the current penetrates towards the 

 south from the Argentine basin has, however, been somewhat uncertain. Arguing from 

 the sudden fall in the temperature and salinity of the deep water towards the south 

 between 43 and 50 S in 30° W, and from the curving of the contours of the 600 decibar 

 isobaric surface towards this region from the Drake Passage, Clowes (1933) concludes 

 that in 30 W the southward movement of the North Atlantic current comes to an end 

 in 46 S, and he regards the deep water found between this latitude and 55 S as 

 water of Pacific origin. 



