DEEP CURRENTS: INDIAN OCEAN 97 



given by Thomsen (1933, fig. 3) based on the data obtained by the 'Planet', ' Snellius' 

 and ' Dana', suggests that the volume and salinity of the north Indian deep current are 

 subject to large variations, probably related to the changes of salinity in the coastal 

 regions, and to the current differences brought about by the changes of the monsoon 

 winds, and variations in the south equatorial current. Another indication that the deep 

 water circulation of the ocean may undergo large changes is pointed out by Moller 

 (1933, p. 235); in the equatorial region of the eastern part of the ocean the ' Snellius' 

 found that the Antarctic intermediate current was strongly developed with a salinity of 

 less than 34-6 °/ 00 , but at the Dana stations 5 farther north there was no sign of it. 

 Moller suggests that unless this difference can be shown to be the result of some 

 hitherto unknown morphological feature south or south-west of the Bay of Bengal, it 

 must be regarded as evidence of a great fluctuation of the deep water circulation. 



The observations made by the ' Snellius ' and ' Dana ' also show that no deep current 

 comparable with that which flows from the Arabian Sea and its adjoining gulfs is formed 

 in the north-eastern part of the ocean (Moller, 1933, p. 234), and the salinity distribu- 

 tion in the cross-section from west to east across the ocean in 8° N to 2° S shows that 

 the deep water formed in the western part of the ocean spreads towards the east. 



The existing data are still insufficient to show the exact part played by the Atlantic 

 deep current in the Indian Ocean. The high salinity and oxygen content in the south- 

 western part of the ocean (Figs. 19, 21) suggest that the lower strata of the deep water 

 are largely of Atlantic origin, but the decrease of salinity and oxygen content towards the 

 east indicates that east of 40 E the layer may contain a large proportion of water from 

 the north Indian deep current. It is, however, probable that some of the Atlantic water 

 finds its way right across the ocean. The observations of the ' Dana ' and ' Snellius ' so 

 far published indicate that the deep water found at St. 878 (section 10, Plates XIX-XXI), 

 about 200 miles south-east of Cape Leeuwin, the south-western extremity of Australia, 

 with a salinity of as much as 3478 % , is too saline to have its origin entirely in the 

 north Indian current, and suggest that it belongs chiefly to an eastward movement of 

 Atlantic water. It is, however, not quite safe to draw such a conclusion at present ; 

 in view of the possibility that there are large fluctuations in the deep water circulation 

 of the ocean, the data from the north-western area are too scanty to give final information 

 about the salinity of the north Indian deep current. 



In the Southern Ocean, the need for a compensating current towards the south in the 

 deep layer, and the influence of the prevailing west wind may be supposed to cause the 

 deep water to flow south and east. The data obtained along sections 8 and 9 (Plates 

 XIII-XVIII) support this conclusion. The southward movement is probably strongest 

 in the eastern part of the Atlantic-Antarctic basin, between 50 E and the Kerguelen- 

 Gaussberg ridge (see Figs. 19-22, section 9, and Plate XLIV), and again south of 

 Australia. East of the Kerguelen-Gaussberg ridge (Sts. 861-4, section 9) the southward 

 movement appears to be weaker, whilst the northward movement in the bottom layer 

 is stronger. The increase in the strength of the bottom current and the decrease in that 

 of the deep current are probably due to the influence of the shallow soundings in the 



D XV *3 



