ioo DISCOVERY REPORTS 



'Challenger' and 'Planet' gave Wiist reason to suppose, however, that the separation 

 of the surface and deep waters was not quite complete, and he suggested that in 0-9 N, 

 in the central part of the ocean between the two intermediate currents, the conditions 

 were such that a limited volume of surface water was able to sink in order to form a 

 highly saline deep current, similar to the North Atlantic deep current, though with not 

 such a high salinity. Although there were not enough data to establish the existence of 

 a highly saline deep layer very definitely Wiist was able to find good reasons for sup- 

 posing that it existed. 



The northward movement in the Antarctic intermediate and bottom layers is itself 

 an almost certain indication that there must be a southward compensating current in 

 the deep layer. Wiist also found (1929, p. 46) that the Challenger observations in the 

 central part of the ocean frequently showed that in the neighbourhood of the 2-25° C. 

 isotherm, between 1500 and 2000 m., the temperature increased slightly with depth, and 

 suggested a stratification in which colder intermediate water lay above warmer south- 

 ward-flowing deep water. The range of the temperature difference was actually found 

 to be not outside the possible limits of error of the Challenger observations, but even 

 the existence of a weak temperature gradient instead of an actual inversion seems to be 

 sufficient to justify Wiist's conclusions. It was also most significant that the salinity was 

 found to increase with depth below the level of the intermediate current, and south of 

 30 N in the western part of the ocean, the high salinities measured by the ' Planet ', 

 3470-3472 °/ 00 and in one instance 3479 °/ 00 (St. 55, is°42' S, i6 5 °44' E) clearly 

 point to the existence of some kind of highly saline current. 



Wiist recognizes the possibility of other highly saline currents than that which might be 

 formed by the sinking of surface water in the region between the intermediate currents 

 in the central part of the ocean. He suggested that a small volume of highly saline deep 

 water may be formed in some of the more or less enclosed basins found in the equatorial 

 regions. The Planet St. 55 (Reichard, 191 1) was made about 270 miles north of an outlet 

 of the Fiji basin. There is also a possibility that some of the highly saline surface and 

 subsurface waters may break through the poorly saline intermediate layer at some point 

 near the coast of Australia between 30 and 35 S, and finally he shows that there may be 

 a deep current from the Indian Ocean into the Pacific Ocean south of Australia ; accord- 

 ing to Moller (1929) it was safe to assume that such a current would have a salinity of 

 more than 3470 °/ 00 . 



After an examination of the Carnegie data of 1928-9, Sverdrup (193 1) concluded that 

 the deep water circulation of the Pacific Ocean was not only quantitatively different 

 from the circulations of the Atlantic and Indian Oceans but also of a different character. 

 In the region examined (approximately 40 S to 50 N, north-east of a line from 40 S, 

 ioo° W to the Fiji Islands and Japan), the deep water below 2000 m. was found to be 

 very uniform, with a salinity of 34-64-34-67 °/ 00 , and Sverdrup regards the longitudinal 

 section through the western part of the ocean drawn by Wiist (1929, pis. i. ii) and the 

 Carnegie data from the central part of the ocean as sufficient evidence that this water 

 cannot be formed by the sinking of surface water in the equatorial region. He also 



