VERTICAL CIRCULATION IN THE OCEAN iS7 



water to the north of the convergence has a high oxygen content of nearly 6 c.c./litre. 

 On the northern side of the convergence the region of mixing is clearly seen, reaching to 

 about 1 500 m. The water of the intermediate return current contains much less oxygen, 

 i.e. less than 4 c.c./litre. Within the deep water we find a small oxygen content in the 

 northern part, but the ascending deep water contains more, while the north-flowing 

 bottom water shows the highest oxygen content. 



Section V (Figs. 14-17) passes through the Scotia Sea. The observations were taken 

 by the ' Discovery II ' in the beginning of March, 193 1. Several features are similar to 

 those of the more western sections. Examining the temperature and saUnity sections 

 we recognize in the extreme northern part the Antarctic intermediate water of about 

 3° and 34-I-34-2 °/oo and, in the central part of the section, the intermediate return 

 current. This rises from about 1000 m. in latitude 54° 30' S to about 400 m. in latitude 

 58° S and carries water of about 2° and 34-5 °/oo- One new feature is seen. In the 

 southern part we find cold water of a temperature below 0° and of low salinity repre- 

 senting water from the Weddell Sea which has flowed over the ridge between the South 

 Shetland and the South Orkney Islands. 



The phosphate and oxygen sections do not extend as far north as the temperature and 

 salinity sections because no observations of phosphate and oxygen were made at St. 653. 

 The incomplete sections show, nevertheless, features which are quite similar to those of 

 the sections farther to the west. The water of the intermediate return current shows 

 high phosphate and a low oxygen content. The cold water of the Weddell Sea is rich in 

 oxygen but contains less phosphate than the south-flowing water. 



The last section, section VI (Figs. 18-21), follows the meridian of 30° W in the 

 Atlantic and reaches from about 58° S to almost 34° S. The observations were taken by 

 the 'Discovery 11' at the end of April, 1931. The distances between the stations are 

 great and, therefore, the horizontal scale has been reduced to one-half. This should be 

 borne in mind when studying the section. 



The north-south extension of the section VI is so great that both the Antarctic and 

 the sub-tropical convergences are seen. The former is here situated slightly to the north 

 of 50° S, while the latter is found at about 40° S. To the north of the Antarctic Con- 

 vergence the sinking of the water and the northerly flow of the Antarctic intermediate 

 current are clearly seen from the salinity section. After having left the upper layers the 

 Antarctic intermediate water flows horizontally at a depth of about 400 m., but shortly 

 before reaching the region of the sub-tropical convergence it sinks further down, to 

 about 1000 m. in the northern part of the section. The salinity increases somewhat, 

 from less than 34-2 7„„ to nearly 34-3 7oo> but the temperature remains nearly constant 

 at 4°. The oxygen content is high, between 5 and 5-5 c.c./litre, but the phosphate con- 

 tent is relatively low and varies between no and 120 mg. PgOg/m.^ The temperature 

 section indicates as previously the existence of a warm intermediate return current to- 

 wards the south. This current begins in the region of mixing to the north of the Ant- 

 arctic Convergence and on its southwards course it rises from a depth of about 900 m. 

 in 46° S to about 400 m. in 56° S. The water of this current is rich in phosphate, 



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