ANTARCTIC SURFACE WATER: WEST WIND DRIFT 35 



the current towards the east; according to Ekman (1928) the deep current caused by the 

 wind will be deflected to the left as the soundings decrease, and to the right when they 

 increase. The deep current in the Southern Ocean, although not a true slope current, 

 will no doubt be affected in a similar way, and its deviations communicated to the sur- 

 face current. Evidence from other regions suggests that the convergence will follow 

 approximately the same course as the isotherms. There is no indication that it bends 

 northwards between the Crozet Islands and Kerguelen owing to the existence of a 

 strong bottom current through the gap in the Atlantic- Indian Ocean cross-ridge; if the 

 bottom water finds an easier outlet through the deep channel and is not pent up behind 

 the ridge, the warm deep layer can, however, be expected to slope less steeply, and, 

 helped by the effect of the increasing depth on the deep current, the convergence will 

 recede towards the south. 



The data available from higher latitudes in the western part of the Indian Ocean show 

 that east of 40 E the 1 and 2° C. isotherms lie as much as 200-300 miles farther south 

 than they do in the eastern part of the Atlantic Ocean. The northern limit of pack-ice 

 also recedes towards the south in this region, and its high latitude has been used as 

 evidence of a surface current towards the south (see p. 30). It is, however, not necessary 

 to assume that there is such a current ; there may be a general movement towards the 

 north throughout the two regions, the high temperature and freedom from pack-ice 

 of the water east of 40 E showing that the northward movement is much weaker there. 

 The bending of the isotherms and the pack-ice limit towards the south may also be due 

 to a decrease in the strength of the movement which carries Weddell Sea water eastwards 

 across the Atlantic Ocean, and to the gradual disappearance of this water as it sinks 

 towards the north or mixes with the neighbouring waters. 



There is no indication of a movement of sub-Antarctic water southwards over the 

 Antarctic water in the western part of the Indian Ocean, and the assumption of a small 

 northward movement is more in keeping with the observations in section 8. 



East of the Kerguelen- Gaussberg ridge there seems to be a strong northward current 

 in which the water from the westerly current close to the continent finds its way north- 

 wards (see p. 31). Actually the current appears to be strongest at St. 861 (section 9, 

 Plates XVI-XVIII) on the eastern slope of the ridge and at St. 864 which is almost 

 north of the Shackleton ice-shelf. According to Ekman 's theory the easterly current 

 should bend southwards on the eastern slope of the ridge, but the data are not sufficient 

 to allow the relation between the northward movement and the factors which cause it 

 to be examined very closely ; the ridge runs approximately north-west to south-east, 

 and the northward movement east of the ridge may be due to water being deflected 

 northwards in a higher latitude. 



Section 9 also shows that there is a stronger movement of bottom water towards the 

 north on the eastern side of the ridge, and it may be this current, acting as a false bottom 

 to the sea, which causes the easterly currents in the deep and surface layers to be 

 deflected northwards. The observations at Sts. 862 and 863 show that between the 

 strong northward movements- at Sts. 861 and 864 there is an area of weaker movement, 



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