SOUNDINGS TAKEN DURING THE DISCOVERY INVESTIGATIONS, 1932-1939 87 



but soundings obtained on the Pacific ice-edge suggest that a wide continental shelf exists in this 

 sector. No land has been seen to the south from the various ships which took these soundings, and 

 it may therefore be assumed that the shelf has a minimum width of 15 to 20 miles. 



Off Marie Byrd Land and as far west as Cape Colbeck the bottom rises abruptly to a narrow shelf 

 which widens out into the shelf which extends over the whole area of the Ross Sea (see PI. XXV). 

 At Cape Adare, at the north-western corner of the Ross Sea, the bottom again rises sharply from deep 

 water to a narrow coastal shelf, and these conditions prevail to the west as far as the meridian of 158^ E. 

 Between this meridian and that of 130° E there is a wide area to seaward of the land where shallow 

 soundings obtain, and in January 1938 off Adelie Land the ' Discover}^ II ' took continuous soundings 

 with the 'Acadia' recorder between 63° 53-1' S, 135° i6-8' E and 66° 13-8' S, 139° 46-4' E. The 

 distance run was 170 miles, in approximately 19 hr., and the true course was south-east. Unfortu- 

 nately, the weather during the last 12 hr. of this run was overcast and there were intermittent heavy 

 snow squalls ; these conditions, together with the unreliability of the magnetic compasses due to the 

 close proximity of the South Magnetic Pole, made it impossible to assign positions for the soundings 

 which would be acceptable for plotting on the charts. However, the accuracy of the positions, which 

 were obtained by dead reckoning, is sufficient to prove the existence here of a wide continental 

 shelf. 



The run in to the land commenced at depths of approximately 2200 fm. (4023 m.) and the bottom 

 remained fairly level at this average depth for about 40 miles. In approximately 64 S, 135^ 30' E the 

 character of the bottom began to change and depths became very irregular. Soundings in general 

 shoaled gradually to depths between 1200 and 1300 fm. (2195 and 2377 m.) during the next 60 miles 

 of the run, and then remained approximately at this level for some 15 miles farther to the south-east. 

 The bottom was still very irregular and there was no indication of a slope up towards land when, 

 unfortunately, the magnetic coil in the head of the transmitter fused. A new coil was fitted and 

 continuous soundings were resumed within an hour, but by this time the depth was 712 fm. (1302 m.) 

 and it was obvious from the record that the slope up to the continental shelf had commenced. The 

 edge of the shelf was reached in a distance of 3-65 miles from the resumption of soundings, at a depth 

 of 247 fm. (452 m.). This represents a slope of just over 7° on a line of approach which was probably 

 at an angle of 45° to the lines of the contours; the actual slope, measured at 90^ to the contours, will 

 almost certainly be greater. 



After passing over the edge of the shelf which, at this point, lay in 65° 17-3' S, 138'' 19-5' E (50 miles, 

 approximately, north of Adelie Land), depths gradually increased to a maximum sounding of 335 fm. 

 (613 m.) in 65° 39' S, 139 08' E. From this position soundings shoaled fairly rapidly to a depth of 

 244 fm. (446 m.) in 65° 45' S, 139° 22' E and continued near this level until the deterioration of the 

 weather forced us to abandon the approach in approximately 66° 14' S, 139° 46' E. The sounding in 

 this position was 265 fm. (485 m.). 



West of Adelie Land, as far as the meridian of 100^ E, the line of the coast is in considerable doubt, 

 but there is some slight indication of a fairly wide submarine shelf to seaward of the land. Between 

 100° E and 60° E the presence of a continental shelf is in general well established ; its width is variable 

 but gradually narrows towards the west. In 98° E it stretches out for at least 130 miles from the 

 continent, but off Kemp Land, in approximately 60° E, the seaward limit of the shelf lies not more 

 than 30 miles off the land. 



Profiles, based on the continuous sounding records, have been drawn for the approach to the 

 continent in the meridian of Greenwich and also for the run in to Adelie Land; they are shown in 

 Text-fig. 17 (p. 88) and, in conformity with the profiles across the Scotia Sea and Arc, the vertical 

 scale is magnified 25 times. 



