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HYDROLOGY OF THE SOUTH ATLANTIC 



the effect of vertical mixing is greatest, and least at the level of minimum salinity which 

 forms the nucleus of the layer. 



It is difficult to trace the changes in the upper stratum of the layer, since the path of 

 the water is not indicated by any maximum or minimum in temperature or salinity which 

 can be followed. The water which has a temperature of more than 10-5° C. has been 

 considered to be sub-tropical, and the origin of much of the water in the sub-tropical 

 layer must be in Antarctic intermediate water, which has been warmed, and had its 

 salinity increased, by mixing across the discontinuity. 



In the bottom of the Antarctic intermediate layer, at the level of minimum tempera- 

 ture, the changes can be followed more easily. The temperature at this level increases 

 from 278° C. in 34° 08' S to 4-12° C. in 03° 19' S, and the salinity from 34-62 '7oo in 

 34° 08' S to a maximum of 3473 7 00 in about 18° S. The increase in temperature is the 

 result of mixing with the warmer waters which lie both above and below it. The increase 

 in salinity is the result of mixing with the more saline water below and the less saline 

 water above. North of 18° S the salinity in the level of minimum temperature de- 

 creases from 3473 to 34-59 7oo in 03° 19' S, because there is an increasing percentage 

 of Antarctic intermediate water in the mixture at this level. 



The changes of temperature and salinity at the level of minimum salinity, where the 

 layer is least changed by vertical mixing, are most interesting. They are shown, together 

 with the figures for oxygen content, in the following table. 



* This value obtained graphically. 



It will be seen from this table that the temperature and salinity both increase towards 

 the north as a result of vertical mixing. The increase is approximately proportional to 

 the distance the water travels ; but it is not regular, and there are patches of warmer 



