ANTARCTIC BOTTOM WATER: MOVEMENTS in 



of the sea and towards the north along the east coast of Graham Land also tends to make 

 the water sink in the coastal region. This effect is also likely to be more powerful in the 

 Weddell Sea than in any other Antarctic sector, because of the exceptionally high lati- 

 tude to which the sea penetrates and because the westward movement is not confined 

 to the surface layer as it principally is in the other sectors, but extended to the deep and 

 bottom layers. 



The temperature distribution suggests that the principal movement of the bottom 

 water from the Weddell Sea is towards the east across the Atlantic Ocean ; but the low 

 temperature of the bottom water farther north shows that there is also a strong north- 

 ward movement. In the western half of the ocean Wiist (1933) has traced the current 

 to as far as 40 N. 



The distribution of bottom temperature in the Scotia Sea leads Wiist to suppose that 

 some of the bottom water from the Weddell Sea flows through a gap in the southern 

 part of the Scotia Arc, between the South Orkney Islands and the South Sandwich 

 Islands, into the Scotia Sea. On the grounds of the lowest potential temperature re- 

 corded, — 0-62° C. at the Deutschland St. 179, he concludes that the depth of the gap in 

 the ridge is 2750 m., so that water from that level in the Weddell Sea can pass through 

 it, and with the help of the Deutschland soundings and the temperature distribution he 

 fixes the longitude of the gap as 34— 35 W. In November 1932 the ' Discovery II ' made 

 a single line of soundings across the same region, and although they have not yet been 

 examined carefully they show the possibility that there is a gap through the ridge in 

 33— 34 W. They do not prove its existence, however, and subsequent work may show 

 that there is no gap. The evidence of the low bottom temperatures in the Scotia Sea is 

 also not a certain indication that bottom water finds a passage through the ridge from 

 the Weddell Sea. It has already been shown that Antarctic bottom water may be 

 formed in winter between the South Shetland Islands and the South Orkney Islands, 

 on the borders of the Scotia Sea itself. At St. 169 in 6o° 49' S, 51 00' W (Station 

 List, 1929) and in the small deep basin just north of the South Orkney Islands potential 

 bottom temperatures as low as — o-8o and -o-68° C. have been measured. These 

 temperatures are lower than those described by Wiist in the neighbourhood of 33- 

 35 W, and they suggest that the cold bottom water may be formed in the southern 

 part of the sea west of the South Orkney Islands. 



Wiist also shows that the cold bottom water spreads a short distance towards the west 

 from the Scotia Sea into the Drake Passage where it mixes with the bottom water of the 

 Pacific Ocean. The boundary between the two waters seems to be very well defined and 

 between 60 and 70 W the isotherms run almost north and south. There appears to be 

 no great bottom current either towards the east or west from one ocean to the other. 



The principal northward movement of bottom water in the Atlantic Ocean takes 

 place through the deep passage between the Scotia Arc and the mid-Atlantic ridge 

 (Plate XLIV). Wiist (1933) has shown that the Antarctic water from this current can be 

 traced over a distance of ioo° of latitude. In the western Atlantic basin it flows directly 

 to 40 N ; it also enters the east Atlantic basin through the Romanche Channel — a deep 



