OCEANOGRAPHY 425 



west (the Brazilian Deep and the Argentine Deep) and two on the 

 east (the West African Deep and the South African Deep). Now 

 it has been found that the "bottom water" in these great deeps — 

 the bottom lies more than 5,000 metres (2,725 fathoms) below the 

 surface — is not always the same. In the two western deeps, off 

 South America, the temperature is only a little above 0° C. We 

 find about the same temperatures in the South African Deep, and 

 farther eastward in a belt that is continued round the whole earth. 

 To the south, between this belt and Antarctica, the temperature of 

 the great deeps is much lower, below 0° C. But in the West 

 African Deep the temperature is about 2° C. higher; we find there 

 the same temperatures of between 2° and 2'5° C. as are found 

 everywhere in the deepest parts of the North Atlantic. The 

 explanation of this must be that the bottom water in the western 

 part of the South Atlantic comes from the south, while in the 

 north-eastern part it comes from the north. This is con- 

 nected with the earth's rotation, which has a tendency to deflect 

 currents to the left in the southern hemisphere. The bottom 

 water coming from the south goes to the left — that is, to the 

 South American side; that which comes from the north also goes 

 to the left — that is, to the African side. 



The salinity also decreases from the surface downward to 

 600 to 800 metres (about 300 to 400 fathoms), where it is only 

 a little over 34 per mille, but under 34 '5 per mille; lower down it 

 rises to about 34 '7 per mille in the bottom water that comes from 

 the south, and to about 34 '9 per mille in that which comes from 

 the North Atlantic. 



We mentioned that the Benguela Current is colder and less salt 

 at the surface than the Brazil Current. The same thing is 

 found in those parts of the currents that lie below the surface. 

 This is clearly shown in Fig. 9, which gives the distribution of 

 temperature at Station 32 in the Benguela Current, and at 

 Station 60 in the Brazil Current; at the various depths down 

 to 500 metres (272'5 fathoms) it was between 5° and 7° C. colder 



VOL. II. 53 



