ANTARCTIC BOTTOM WATER 107 



monstrated time and again ; it has been found to flow along the sea bottom and it is 

 also known to exist in the Indian and Pacific Oceans. Although the current is so well 

 known, however, its exact mode of formation in the Antarctic region is still a matter 

 of question. 



Brennecke (1921, p. 140) pointed out that the observations made during the cruise 

 of the ' Deutschland ' and the drift of the 'Endurance' showed that the Antarctic 

 Continent south-west of the Weddell Sea was bordered by a wide continental shelf on 

 which there was a depth of only a few hundred metres. On this shelf the water is cooled 

 right through in winter by convection, and its salinity, already high, is increased as fresh 

 water is removed and salt left behind when sea-ice is formed. Brennecke suggested that 

 the great density of this water would make it sink from the shelf to flow northwards as a 

 bottom current. 



Drygalski (1926, pp. 495-7) deduced a similar mode of formation from the Gauss 

 data and regarded the bottom water as deep water which had been cooled by contact 

 with the cold surface water. There was, however, a difficulty in accepting this explana- 

 tion, because the cold shelf water found by the ' Gauss ' in 90 E had a very low salinity ; it 

 could not be mixed with the deep water in sufficient quantity to give water of the same 

 temperature as the bottom water without the salinity of the mixture becoming far too 

 low, and in a later paper (1928, p. 278), Drygalski was forced to add that the cooling of 

 the deep water was also effected by climatic influences— presumably through contact 

 with the air. As far as is known at present, however, the deep water never comes into 

 contact with the air, since it is always covered by the poorly saline surface layer, and it 

 is more just to interpret the Gauss data as showing that the bottom water in 90 E is not 

 formed in situ ; it cannot be formed without some addition of cold and highly saline 

 water from another source. 



Schott (1926, p. 428) pointed out that the existing data did not prove that the mode of 

 formation of the bottom water was fundamentally different from that described by 

 Nansen (1912) for the formation of bottom water in the Arctic regions. Nansen sup- 

 posed that over extensive regions south-east of Greenland, and north and south of Jan 

 Mayen, the water became completely mixed from surface to bottom during the winter, 

 so that the cold surface water could find its way directly into the bottom layer. Wiist 

 (1928) had similar views and suggested that the Antarctic bottom water was formed by 

 the sinking of cold and highly saline surface water in the central part of the Weddell Sea 

 when the cyclonic circulation which prevails there slows down in winter. In a later paper, 

 however (1933, pp. 44-8), he attacks the problem from a new standpoint— that of the 

 potential temperature distribution, and finds that the coldest bottom water is formed 

 as suggested by Brennecke in the south-western part of the sea. While believing this, 

 however, he does not abandon the application of Nansen's principles to the Weddell 

 Sea and supposes that the less cold bottom water— that with a potential temperature 

 between -0-2 and -0-7° C— is formed by the sinking of cold surface water in winter 

 in a region which extends across the Atlantic Ocean from the region between 60 and 

 66° S in the Weddell Sea to that between 56 and 6o° S in the eastern part of the ocean. 



14-2 



