IS6 DISCOVERY REPORTS 



'William Scoresby ' at the end of February, 1929, and one made by the ' Discovery 11' 

 in the middle of April, 1930. In the two years the conditions were rather different, but 

 in both years the tongue of water with high temperature was present. In 1929 it reached 

 almost from the northern to the southern side of the Passage, but in 1930 it extended 

 only from the middle of the Passage to the southern side. In 1929 the tongue appeared 

 to be divided, indicating that the southward flow took place at approximately the levels 

 of 400 and 900 m., except in the most southerly region where the two branches appeared 

 to unite. In 1930 only one tongue with an axis at about 500 m. was present. In the 

 southern part of the Passage the 1° isotherm shows in both sections a downwards bend, 

 which perhaps indicates that part of the deep water which flows south turns back and 

 joins with the north-flowing bottom water. 



In both sections the distribution of salinity indicates that on the northern side of the 

 convergence the intermediate Antarctic current flows with a northerly component at 

 depths between 400 and 700 m. The salinity of the north-flowing water is between 

 34-2 and 34-3 °/oo, while the surface saUnity of the upper layers is lower. The salinity of 

 the descending water must, therefore, have been increased by mixing with deep water, 

 and such an increase, owing to mixing, appears to have still more influenced the salinity 

 of the intermediate current which returns to the south. The water of this current has 

 a salinity of 34-5-34-6 °l^^. The mixing seems principally to take place at some depth 

 below the convergence. 



Observations of phosphate are available from both years, and by means of these the 

 vertical sections in Figs. 7 and 10 have been constructed. These show that the maximum 

 phosphate values are found directly above or within the intermediate return current. 

 Both the vertical and the horizontal extensions of the phosphate maxima agree re- 

 markably well with the position of the current, and later on we shall discuss the 

 significance of this feature. 



The next section, section IV (Figs. 11, 12 and 13), lies about 300 km. to the east of 

 sections II and III. The observations were taken by the 'Discovery II' in the middle 

 of March, 193 1 . The temperature section shows features which are quite similar to those 

 of the more western sections. To the north of the convergence we find a region of mixing 

 within which the descending current is divided into two branches, one which continues 

 to the north at depths of 400-700 m., carrying water of a temperature of about 4° and 

 salinity 34-2 °l'^^, and one which returns to the south at a depth of about 400 m., carrying 

 water of about 2° and 34-6 °l^^ . North of the convergence the region of mixing appears 

 to reach to a depth of about 1500 m. It is interesting to note that the temperature dis- 

 tribution in section II shows features which are intermediate between those of sections I 

 and IV. 



Below the intermediate currents a vertical circulation of the deep water again appears 

 to be present. The downward bend of the 1° isotherm which was seen in sections II 

 and III is also conspicuous in section IV. 



No phosphate observations were made at section IV, but observations of oxygen were 

 undertaken and they give a very interesting picture (Fig. 13). The Antarctic intermediate 



