104 



OBSERVATIONS AND RESULTS IN PHYSICAL OCEANOGRAPHY 



A constant potential temperature over a wide area is 

 generally attributed to the influence of heating from be- 

 low, from the interior of the earth, and it is assumed 

 that the horizontal currents must be very slow where a 

 constant potential temperature can be developed. Exam- 

 ples of a constant or even a downward increasing poten- 

 tial temperature are known from the deep basins in the 

 region of the East Indian Islands, and here one probably 

 finds stagnating water in the great depths. The fact that 

 the potential temperature appears to decrease toward 

 the bottom in the North Pacific indicates that the bottom 

 water is not stagnating but is being renewed. The rela- 

 tively high oxygen content and the increase of this con- 

 tent toward the bottom strongly support the opinion that 

 a renewal of the bottom water by horizontal transport 

 takes place. The low bottom temperatures in the South 

 Pacific point toward a more rapid renewal of the bottom 

 water in this part of the Pacific. No oxygen observations 

 are available from these stations and therefore we are 

 unable to obtain a verification of our conclusions. 



The origin of the deep water of the Pacific has been 

 discussed previously (Sverdrup, 1931). It was pointed 

 out that the deep water cannot be formed by the sinking 

 of surface water in the central part of the ocean (com- 

 bined with processes of mixing) because the deep water 

 is separated from the surface water by a layer of mini- 

 mum salinity. It was also shown that the deep water 

 could not be formed in the neighborhood of the Antarctic 

 Continent because the temperatures are too high. We 

 may add that, for the same reason, the deep water can- 

 not come from the Bering Sea. Furthermore, it is not 

 probable that bottom water of low temperature is formed 

 in the Bering Sea by the processes which have been de- 

 scribed by Nansen, because the surface salinities in the 

 Bering Sea appear to be too low, if we judge from the 

 salinity of the surface current which enters the Pacific 

 Ocean. 



The available data strongly point in the direction 

 that water of the same type as the deep water of the Pa- 

 cific is formed in the eastern part of the Indian Antarc- 

 tic Ocean and that the origin of the deep water of the 

 Pacific has to be sought there. In order to explain this 

 formation, it was assumed that Antarctic bottom water 



Table 11. Stations at which a decided temperature 

 increase toward the bottom was observed. 



♦Values probably 0.03 o/oo too low. 



of low temperature and relatively high salin'ty was 

 formed everywhere on the continental shelf of the Ant- 

 arctic Continent. This water would sink to great depths 

 and contribute toward the formation of cold bottom water 

 which would tend to spread toward the north but, owing 

 to the rotation of the earth, would be deflected to the left 

 and flow along the continent from east to west. A com- 

 plete circumpolar flow would, however, not be developed 

 since the submarine ridge between South America and 

 the Antarctic Continent would present a serious c'lstacle 

 to a flow of the bottom water toward the west. In the re- 

 gion of the Weddell Sea the bottom water, the.-efore, 

 would be deflected toward the north and a great part of 

 this water would enter the western basin of the South 

 Atlantic Ocean. Furthermore, it was assumed that this 

 inflow of cold bottom water was in part responsible for 

 the outflow from the Atlantic of warmer and more saline 

 deep water at some higher level. This flow of Atlantic 

 deep water must also be deflected toward the left which, 

 in this case, means to the east, and the Atlantic deep 

 water must, therefore, enter the Indian Ocean as pointed 

 out by L. MoUer (1929) and clearly demonstrated by 

 Wust (1935). In the Antarctic Ocean to the south of the 

 Atlantic and the Indian oceans, mixing between these two 

 types of water, the cold Antarctic bottom water and the 

 warmer Atlantic deep water, must take place and, as a 

 result of these processes of mixing, a water type is 

 formed which is similar to the deep water of the Pacific. 

 It was assumed that this water enters ithe Pacific 

 through the passage between New Zealand and the Ant- 

 arctic Continent. 



This hypothesis concerning the formation of the deep 

 water of the Pacific was advanced at a time when no re- 

 liable deep-sea observations were available from the 

 vicinity of the Antarctic Continent except in the Weddell 

 Sea area. Since that tine a considerable amount of 

 oceanographic work has been carried out on the expedi- 

 tions with Discovery II , on the British Australian New 

 Zealand Antarctic expeditions conducted by SirDouglas 

 Mawson, and on the Norwegian expeditions organized by 

 Mr. L. Christensen. The observations from these vari- 

 ous expeditions have not yet been published, 1 but the 

 writer has had opportunity to examine the results from 

 the British Australian New Zealand Antarctic expedition 

 and to become acquainted with results from L. Christen- 

 sen's cruises. The new information necessitates con- 

 siderable modification of the views which were present- 

 ed in 1931 but the most important conclusion, that the 

 deep water of the Pacific Ocean is formed in the Antarc- 

 tic Ocean and enters through the passage between New 

 Zealand and the Antarctic Continent, remains unaltered. 



It is now evident that a considerable formation of 

 Antarctic bottom water takes place only within the area 

 of the Weddell Sea. H. Mosby (1934) has shown that the 

 bottom water in the Weddell Sea is formed by mixing of 

 deep water (temperature about 1° C and salinity about 

 34.70 per mille) and water from the continental shelf 

 which has been cooled to freezing point (about -l.^SS C ) 

 and which has attained a salinity of about 34.60 per 

 mille, owing to the processes of freezing. The result- 

 ing bottom water has a temperature of about -0.°6 C and 



^The observations in physical oceanography in the 

 British Australian New Zealand Antarctic expedition 

 have been published by A. Howard (1940) and have been 

 discussed by H. U. Sverdrup (1940). 



