SOUTH SHETLAND ISLANDS AND ADJACENT WATERS 229 



main connecting ridge, is the more pronounced, having a depth of water in one place of 

 only 487 m. (60° 11' S, 50" 28' Wapprox.) and in another of 501 m. (60''-' 15' S, 51' 50' W 

 approx.). The main ridge is quite well defined, but the least depths over the correspon- 

 ding portions are 1501 m. in 60° 25' S, 48"^ 43' W, and 1523 m. in 60'' 37' S, 49 "" 40' W 

 (both positions approximate). Fig. 2 c, which is based on a line of echo soundings run 

 in December 1930 from north to south across the ridge in approximately 49° 40' W, 

 shows the double ridge very clearly. Fig. 3 b, which is based on a line of soundings across 

 the Scotia Sea in 1932, shows a section across the ridge in approximately 48 ' 20' W, 

 where the formation appears to be the same. This double ridge fades away in about 

 51° 40' W, from which point a broad shallow ridge continues to Clarence Island. The 

 depth of water between the ridges is about 3000 m., but at one point there is an abrupt 

 descent, apparently of about 45°, to 5000 m. at which depth a trench also occurs between 

 the eastern end of the secondary ridge and the South Orkneys. 



Hydrological observations made in 1930 on each side of the supposed line of the ridge 

 gave valuable confirmation of the theory of a connexion. It was found that entirely 

 dissimilar conditions, both of temperature and salinity, existed on the two sides, and 

 that these conditions were such as could only have been caused by a submarine ridge of 

 considerable height interrupting the free interchange of water between the Weddell Sea 

 and Scotia Sea. 



This section of the arc from the South Orkneys to Clarence Island may be termed the 

 last oceanic sector, as over the remaining distance from Elephant Island to the South 

 Shetlands comparatively shallow depths are to be found. These will be considered in the 

 remarks on the bottom relief of the Bransfield Strait and the waters adjacent to the 

 South Shetlands. 



SOUNDINGS IN OTHER LOCALITIES 



SOUTH SHETLAND ISLANDS AND ADJACENT WATERS 



(Plate XLVII, Chart 6) 



The Bransfield Strait, which lies between the South Shetlands and Trinity Peninsula, 

 and the area east of it as far as Elephant and Clarence Islands, have been extensively 

 sounded out. The total number of soundings on which our bathymetric chart (Plate 

 XLVII) is based is about 1500, of which number approximately 1400 were taken in the 

 ' Discovery II ' by the echo method. The remainder consist of a line of echo soundings 

 taken by the ' Meteor' during her visit to Deception Island in January 1926,^ and a few 



^ These soundings appear to have been calculated from a constant speed of sound in sea water for all 

 depths, i.e. 1490 m. per sec. {Wiss. Ergebn. Deutsch. Atlant. Exped. 'Meteor', i, Beilage XII), and by 

 this method, if the Admiralty tables of the speed of sound in sea water for this area are accepted, soundings 

 above 5000 m. will be too deep and those below this figure too shallow. In the bathymetric chart no attempt 

 has been made to reduce these soundings to the speeds given in the Admiralty tables, as the differences are 

 not sufficient to have any appreciable effect on the contours concerned. 



