HYDROLOGY OF THE SOUTH ATLANTIC 221 



the Antarctic Continent to fill the deep polar basins and then flows northwards along 

 the sea bottom. It has been called Antarctic bottom water. 



ANTARCTIC INTERMEDIATE WATER 



STRUCTURE AND DEPTH OF THE ANTARCTIC INTERMEDIATE 

 LAYER, AND THE ORIGIN AND MOVEMENTS OF ANTARCTIC 



INTERMEDIATE WATER 



The Antarctic intermediate layer is distinguished in any vertical series of observations 

 made in the sub-tropical or tropical Zones, by its low salinity. Below the sub-tropical 

 water the salinity decreases until it reaches a minimum value, and then it increases. The 

 water on either side of the level of minimum salinity is Antarctic intermediate water. 

 It has its origin in the region of intense mixing just north of the Antarctic convergence. 

 The path of the water forming the layer can easily be followed in Plate VIII which 

 shows the vertical distribution of salinity along the meridian of 30° W. 



In the Antarctic intermediate layer three strata may be distinguished, (i) At the 

 bottom of the layer, where the temperature is lowest, there are the last traces of Antarctic 

 surface water, which have sunk from the cold stratum of the Antarctic surface layer, 

 (ii) At the level of minimum salinity the water has its origin in the mixture of lighter 

 Antarctic surface water and sub- Antarctic water which is formed just north of the 

 Antarctic convergence, (iii) Above the level of minimum salinity there is water which 

 has sunk below the surface in the sub-Antarctic Zone, but north of the region of intense 

 mixing, and is less Antarctic, or more sub-Antarctic, in origin. The greater part of the 

 layer is, however, composed of the water of low salinity which has its origin in the region 

 of mixing just north of the Antarctic convergence. 



The following table shows the depth of the water of minimum salinity in different 



latitudes in 30 ' W. 



Table VII 



Latitude 45° S 40° S 35° S 30° S 25° S 20° S 15° S 



Depth of minimum salinity in metres 380 630 900 940 900 830 700 



Latitude 10° S 5° S 0° 5° N 10° N 15° N 



Depth of minimum salinity in metres 740 700 700 770 800 800 



These depths show the path of the water of minimum salinity which forms the 

 nucleus of the layer as it flows northwards. 



The temperature in the layer decreases until it reaches a minimum value near the 

 bottom of the layer. This level of minimum temperature can be followed as far back as 

 the Antarctic Zone and it is continuous with the level of minimum temperature in the 

 cold stratum of the Antarctic surface layer. The depth of the level of minimum tem- 

 perature is given in the following table for latitudes from 57° 30' S to 5° S in 30° W. 



Table VIII 



7-2 



