2o8 



DISCOVERY REPORTS 



zone. The southerly component has been found in the east of the South Atlantic Ocean, 

 but in the east of the Pacific Ocean it is only found near the sub-tropical convergence. 

 It is not confined to sub-Antarctic water, but also appears in sub-tropical water when 

 there is a prevailing westerly wind. 



Below 200 m. the water in the sub- Antarctic layer has a component of movement 

 towards the north, except perhaps in the eastern corner of the Pacific Ocean. Near 

 Cape Horn, there is a general component in the layer towards the south, for in this 

 region part of the easterly current across the Pacific is deflected southwards to flow 

 through the Drake Passage. 



Conditions in the southern and northern parts of the sub-Antarctic Zone differ 

 rather widely, and the two areas must be considered separately. 



STATION 1021 



200 



W53I8 1 026 



1022 I 1023 1024 |ipg5 



1027 



1028 



400m 



600m 



800m 



200 

 M1LE5 NORTH OF THE CONVERGENCE MILES SOUTH OF THE CONVERGENCE 



Fig. 20. The depth of the minimum temperature in Antarctic surface water and sub-Antarctic 

 water, the depth of the minimum salinity of sub-Antarctic water. 



In the Southern Half of the Zone in the region of intense vertical mixing extend- 

 ing about 100-150 miles north of the Antarctic convergence there are only small changes 

 from west to east. In the Pacific Ocean in 80° W the salinity of the layer is almost 

 uniform with depth down to about 300 or 400 m., or it decreases to a weak minimum 

 at that depth. The temperature is usually uniform down to 150 m. and then decreases 

 gradually. There is sometimes a minimum temperature at the same depth as the minimum 

 salinity, and both are caused by the greater percentage of Antarctic surface water in the 

 mixture of the two waters at that depth. Below the level of minimum salinity the salinity 

 increases, and there are only small temperature changes. At a depth of 600-800 m. the 

 temperature decreases to a minimum, and there is a stratum of comparatively uniform 

 salinity. This is composed of water which has sunk from the cold stratum of the Ant- 

 arctic surface layer. When the Antarctic surface water sinks below the surface, the 

 water in the cold stratum will be least mixed with sub-Antarctic water, because it is 

 much heavier. The warmed and diluted surface stratum of Antarctic surface water has, 

 however, a density not so different from sub-Antarctic water, and mixes more readily 



