SOUNDINGS TAKEN DURING THE DISCOVERY INVESTIGATIONS, 1932-1939 93 



previous data, calls for some modifications of Roos's interpretation (1937) of the ' Bear of Oakland's' 

 soundings. Roos refers to the ' Pennell Bank' as extending right across the Ross Sea from north-west 

 to south-east; he also refers to the ' Iselin Bank', an isolated feature in approximately 72^ S, 177' W. 

 The conception of a shallow bank stretching across the Ross Sea from north-west to south-east 

 appears to have originated with the American Geographical Society's bathymetric map of 1928, and 

 the name 'Pennell Bank' for this feature was proposed by Griffith Taylor (193 1). From the evidence 

 now available it does not appear that this bank is continuous at depths less than 500 m. (273 fm.) across 

 the whole width of the Ross Sea. There is probably a wide area in the north-western part of the Ross 

 Sea where depths of less than 500 m. will be found, and it is highly probable that this is separated by 

 a distance of about 60 miles from two moderately long but narrow areas of less than 500 m. in depth 

 in the south-eastern part of the sea. Both ships obtained a few soundings of slightly less than 500 m. 

 (273 fm.) in this gap, but reference to our present bathymetric chart (PI. XXV) will show that there 

 can be little doubt of the break in the continuity of the 500 m. contour. At the same time there can be 

 no doubt that the general level of the bottom in the gap is above that of the south-western part of the 

 Ross Sea. 



At the eastern side of the larger bank to the north-west of the Ross Sea there is a narrow ridge, 

 some 60 miles in length, where the soundings do not exceed 250 m. (137 fm.). Both the ' Discovery II ' 

 and the ' Bear of Oakland ' ran along this ridge, the latter ship obtaining a minimum depth of 106 m. 

 (58 fm.) in 74° 27' 45" S, 179° 58' W. Since the existence of the original continuous bank across the 

 Ross Sea now is doubtful, we propose that the name 'Pennell Bank' can be appropriately used for 

 this Hmited area of less than 250 m. (137 fm.) in depth. 



In our interpretation of the bottom relief in the region of the so-called ' Iselin Bank' we are of the 

 opinion that this feature is not an isolated bank as suggested by Roos. It seems more probable that it is 

 part of a considerable extension to the north, and finally to the north-east, of the wide shallow area in 

 this part of the Ross Sea. 



The main axis of this large and comparatively shallow region now appears to lie more in a south-west 

 and north-east direction. To the west, between the bank and the Victoria Land Coast, there is a gully 

 with an average depth of between 600 and 700 m. (328-383 fm.) and to the south-west depths of over 

 750 m. (410 fm.) are found north of Ross Island; these depths continue east for some miles along the 

 face of the Barrier and it may well be that greater depths exist under the ice shelf itself. 



It is, perhaps, on the eastern side of the Ross Sea that the greatest value attaches to the soundings 

 of the ' Bear of Oakland '. Before the work done by this ship the information available in this area 

 consisted of six soundings north of the latitude of 73° S and a few isolated depths of less than 300 fm. 

 (549 m.) off-shore between Discovery Inlet and Biscoe Bay. Consequently, our knowledge of the 

 topography of the bottom here was largely guesswork, but two excellent lines of soundings direct to 

 the Bay of Whales, and the run up north to meet the ' Discovery II ' in 72° S, have now provided 

 sufficient evidence on which to draw a series of depth contours. 



It is now evident that, at its seaward limit, the Ross Sea shelf runs approximately in a north and 

 south direction between the latitudes of 72° S and 76° S. Over this distance the shelf is wide and the 

 slope from seaward is only moderately steep. Southward from the latitude of 76° S the trend of the 

 contours is almost in an east and west direction and the width of the shelf is reduced considerably; 

 there is also a marked increase in the angle of slope between the 2000 m. and 500 m. contours. Further 

 work by the 'Bear of Oakland' to the north-east of Cape Colbeck shows, as already noted by Roos, 

 that the shelf is reduced in width to barely 15 miles, with an even sharper slope from seaward. 



There still remains much work to be done in the Ross Sea before a more accurate conception of the 

 bottom relief can be provided. Many more soundings are required between the latitudes of 73" and 



