i88 DISCOVERY REPORTS 



land, where the snow also melts in summer, and the melting of sea ice which has been 

 forming during winter and of land ice brought down to the sea by glaciers. 



It is this fresh water, released in summer and mixed with Antarctic surface water, 

 which streams away from the ice and eventually flows north-east, speeding up the sur- 

 face movements. The eflFect of fresh water on the surface layer will be discussed in greater 

 detail in the section on the temperature and salinity of Antarctic surface water. The 

 direction of the current formed by the addition of fresh water to the Antarctic surface 

 layer will be away from the ice, so that accumulation of water near the ice is prevented. 

 Its direction will be modified by the effect of winds and the eflFect of the earth's rotation. 

 It will also be influenced by the shape of the land masses and the configuration of 

 the sea bottom. 



There are two principal currents of Antarctic surface water in the Falkland Sector. 

 One of these flows towards the north-east out of the Bellingshausen Sea. It has been 

 shown that the westerly winds extend farther south in the Pacific than they do in either 

 the Atlantic or Indian Oceans, and south of 66° S there is still a surface current towards 

 the east. This current is turned towards the north by the west coast of Graham Land 

 and then flows towards the north-east through the- Drake Passage. The distribution 

 of temperature in vertical sections across the Drake Passage shows that the current is 

 strongest at the edge of the continental shelf, for it is there, oflF the South Shetland Islands , 

 that the lowest temperatures are found. 



In the western half of the Scotia Sea the direction of the current is largely influenced 

 by the shape of the bottom. Ekman (1928) has shown that in high latitudes the deep 

 currents in the sea tend to follow the lines of equal depth, and in the Southern Ocean this 

 is not only true of the deep currents but also to a certain extent of the surface currents, 

 to which the effect is transferred by friction or by the effect which a change in direction 

 of the deep current has on the density distribution. North of the Scotia Sea there is a 

 well-defined ridge, the Scotia Arc, extending from Cape Horn and the Burdwood Bank 

 to South Georgia. There is a gap in the ridge between 48 and 49° W^, where the water 

 is deeper than 3000 m., but on the ridge between Cape Horn and 50° W there is nowhere 

 a depth of water much greater than 1000 m. West of 50° W there is a trough of deeper 

 water north of the ridge. The Bellingshausen Sea current is prevented from flowing 

 northwards by the ridge : it follows the easterly direction of the ridge until the gap is 

 reached. At the gap it turns northwards, and then westwards into the deep trough north 

 of the ridge, as well as eastwards across the Atlantic Ocean. The changes in direction of 

 the surface current are reflected in the shape of the convergence in the neighbourhood 

 of 50° W, which is shown in Fig. 11 (p. 191). 



East of 50° W the Bellingshausen Sea current north of the Scotia arc probably has a 

 small component southwards, towards the western end of South Georgia, since the 

 isotherms in the surface recede towards the south. Such a component might be the 

 result of the southward flow of water in the Brazil current, the effect of which on the 

 temperature distribution can be seen in Fig. 8 to the north-east of the Falkland Islands. 



1 Herdman, 1932, pi. xlv. 



