8o DISCOVERY REPORTS 



an examination of the surface current charts published by the Meteorological Institute 

 at De Bilt found that the boundary between the Agulhas current and West Wind Drift 

 showed certain variations, but not obvious seasonal changes. The current boundary as 

 shown by his charts does not, however, coincide exactly with the boundary between the 

 subtropical and sub-Antarctic waters, but the absence of changes in its position agrees 

 with the conclusion that the position of the convergence between the two waters has no 

 regular variation. 



Elsewhere there are not sufficient data to show whether the subtropical water ad- 

 vances farther south in summer or not, but the greater percentage of easterly winds 

 south of Australia, and the change of the current from east to west together with the 

 advance of the isotherms towards the south in summer north of New Zealand (Kriimmel, 

 191 1, pp. 711-12), are indications of such a movement. 



TEMPERATURE AND SALINITY 



Just north of the subtropical convergence the water has a temperature of at least 

 11-5° C. in winter and 14-5° C. in summer, but where there is a strong southward move- 

 ment the water may be as much as 5 C. warmer. The salinity of the subtropical water 

 just north of the convergence is at least 34-9 °/ 00 , but it may be as much as 35-5 °/ O0 . 

 The surface temperature and salinity both increase towards the north. 



In the western part of the Atlantic Ocean it was found that in the neighbourhood of the 

 23 C. isotherm the gradient became suddenly steeper, and farther north the subtropical 

 water was covered with a shallow layer of water which was found to be practically 

 depleted of nutrient salts and separated from the deeper water by a sharp discontinuity 

 (Deacon, 1933, pp. 216-20). There is sufficient evidence to show that similar water — 

 called tropical water to distinguish it from the subtropical — exists in the Indian and 

 Pacific Oceans. It is carried farthest south in the Brazil, Agulhas, and East Australian 

 currents, but it hardly reaches the limits of the Southern Ocean. South-east of Cape 

 Town, however, we found that between 38 59' S, 21 35' E and 40 07' S, 22 30' E the 

 surface temperature was as much as 23-0-23-5° C. in April, and south-east of Cape 

 Leeuwin there was a narrow stream with a temperature of 21 ° C. in May ; the properties 

 of these waters are not very different from those of the tropical water. The regions of 

 high surface temperature are also marked by a high salinity. 



The temperature distribution in the subtropical regions is given in the charts con- 

 structed for the Atlantic Ocean by Schott (1926, pis. ix, x), for the Indian Ocean by 

 Moller (1929, figs. 17, 21) and for the Pacific Ocean by Schott and Schu (1910, pi. i). 

 The salinity distributions in the three Oceans are given by Schott (1934, pi- i). 



THE WARM DEEP LAYER 



One of the most important results of the hydrological work of the circumpolar cruise 

 was the proof that a warm deep layer exists throughout the whole of the Antarctic Zone. 

 The layer and its properties were already well known in the Atlantic Ocean, but in the 

 greater part of the Indian Ocean and in the Pacific Ocean very little was known of them. 



