ALIMENTATION AND DENUDATION OF THE ROSS BARRIER 143 



exceed annual precipitation, and provided also that there were no loss of ice to the 

 Barrier owing to the constant melting of its under surface in the relatively warm 

 deeper water of Ross Sea. 



We know that both ablation and melting, chiefly submarine, are now contri- 

 buting to remove the ice of the Barrier above and below simultaneously. On 

 the whole the Barrier surface * is probably gaining, especially along its southern, 

 south-western, western, and central portions through accessions chiefly of drift snow, 

 partly of snow falling m situ on the Barrier. 



For example, at Captain Scott's Depot " A," near Minna Bluff, the accession 

 of hard snow, almost neve, proved to be no less than 8 feet 2 inches {2'5 metres 

 in round numbers) in 6j years, that is, almost exactly, 15 inches (380'99 millimetres) 

 of hard snow, which was proved by experiment to be equal to 7^ inches of rain 

 (184"15 millimetres) a year. 



As ah-eady explained in the Meteorological Notes, the part of the Ross Barrier 

 nearest to the high mountains of the Antarctic horst and nearest to the sea receives 

 the heavier additions of drift snow, as well as of snow falling in situ. Amundsen 

 records that the surface of the Ross Barrier, between about 80° and 82° S. lat., 

 and near the meridian of 163° W., did not alter appreciably between April 1911 and 

 October 191 l.f 



This area, removed so far from the nearest high mountain, is one of comparative 

 calm, and consequently low snowfall and little drift snow. 



The loss to the Ross Barrier through the constant meltina; of its base in the 

 relatively warm water of Ross Sea is probably considerable, possibly even approxi- 

 mating to about 1 yard ('914 metre) to 1 metre a year. 



Thus as fully sixty years have intervened between the time of Captain R. F. Scott's 

 survey of the Barrier in 1902 and that of Sir J. C. Ross' original examination of it, 

 at the rate of a yard a year no less than 60 yards 180 feet (55 metres) may have 

 been removed by melting from the base of the Ross Barrier. 



Date of latest Phase of Maximum Glaciatioii. (a) Vertical Shrinkage of Ross 

 Barrier. If the mean density of the Barrier Ice be taken as "85 as compared with the 

 average density of the water of Ross Sea taken as unity, the height of the Barrier 

 clifi" may have been lowered by as much as 32 feet (over 9 metres) from this cause 

 alone since the time of Ross' visit in 1842. Unfortunately Ross' survey was not 

 sufficiently detailed to prove whether or not such an actual general decrease in height 

 has taken place. If data were available as to this present rate of dwindling of the 

 ice of the Ross Barrier, some approximate estimate might be formed of the time that 

 has elapsed since the latest phase of maximum glaciation in the Ross Sea region of 

 Antarctica. 



As has been abundantly proved already, the surface of the Ross Barrier has 



* But this surface gain may be more than compensated for by the submarine melting, 

 t The South Pole, vol. i. pp. 233, 234, and 382. 



