8 DISCOVERY REPORTS 



it will sink. It is in this way that the Antarctic surface layer is formed. The movements 

 in the Antarctic surface water in winter have been found to be very small indeed and 

 increase to a maximum in summer when most ice is melting; the salinity of this water 

 is for the same reason greatest in winter and least in summer. Then there is water 

 which has been cooled by contact with ice, but has only been very slightly diluted. It is 

 dense ; and it therefore sinks, forming the cold Antarctic bottom water which fills the 

 depths of the deep polar basins and streams slowly northwards along the bottom. To 

 compensate for the removal of water from the Antarctic regions in the form of surface 

 and bottom water, there is a flow of warmer water towards the pole in the intermediate 

 layer. This is the part played by the water of the warm intermediate layer which is said 

 by Wiist to have its origin in the surface of the North Atlantic Ocean. 1 It is in this 

 intermediate water that the maximum salinity, temperature, phosphate content and 

 minimum oxygen content are found, and the continual upwelling of the water from 

 this richer layer inside the Antarctic region replenishes the salinity and phosphate 

 content of the Antarctic water." 



Fig. 5 shows temperature and salinity curves at two deep-water stations in the Ant- 

 arctic Zone, one to the south-west and one to the north-east of South Georgia; the 

 different character of the three layers is clearly shown in each (the water immediately 

 against the surface is warmed by summer sunshine and atmospheric conditions). 



South Georgia itself is influenced by two currents within the Antarctic Zone, one 

 slightly colder, and more saline, than the other. The colder and more saline current 

 flows out of the north-west corner of the Weddell Sea, and following the curve of the 

 Scotia Arc flows up the north-east side of South Georgia. The slightly warmer current 

 flows from the Bellingshausen Sea through Drake Passage and approaches the south 

 west side of South Georgia. The general course of these currents is shown in Fig. 4. 



The actual details of the water movements immediately around South Georgia must 

 vary from year to year, with slight variations in the strength and direction of these two 

 main currents, and with the varying influence of winds. In the present report we are 

 concerned with the actual state of the water movement at the time of our main survey 

 in December-January, 1926-7, and we are greatly indebted to Mr A. J. Clowes, who 

 has worked these movements out in as complete detail as possible by means of dynamic 

 calculations. He has supplied us with the chart of surface movements which we re- 

 produce in Fig. 6. The Weddell Sea water having been curved round by the Scotia Arc 

 is seen approaching South Georgia from the east and south-east. It flows over the 

 continental shelf and up the north-east side of the island ; some of it also flows round the 

 south of the island, to the west where it mixes with water from the Bellingshausen Sea, 

 over the wide continental shelf to the westward of the island. We see the Bellingshausen 

 Sea water approaching South Georgia from the south-west, and upon meeting the 

 continental shelf being deflected to the north-west. Apparently it swirls round to the 



1 Clowes (1933) has recently suggested with the aid of charts of dynamic topography and temperature- 

 salinity diagrams that south of 46 S the warm and more saline intermediate layer is composed of water of 

 Pacific origin which has entered the region via the Drake Passage. 



