104 



zontal ocean currents that exist to the east and south of the Grand 

 Banks plateau. 



In 1929, the heaviest ice year that the international ice patrol has 

 experienced to date, approximately 1,300 bergs drifted south of the 

 forty-eighth parallel in the Western North Atlantic. When it 

 crosses the forty-eighth parallel the cubical contents of the average 

 berg, above water, is not greater than that of a block of ice 100 feet 

 high, 400 feet long, and 100 feet wide. That means that the average 

 berg has, above water, not more than 4,000,000 cubic feet of glacier ice. 

 Lieut. Commander Edward H. Smith, a former ice-observation officer 

 of the patrol, estimates the average above-water volume of bergs about 

 the Grand Banks to be one-third of this amount. However, a certain 

 amount of glacial ice in the form of growlers crosses the forty-eighth 

 parallel each year. To allow for this ice, and to insure that the total 

 quantity of fresh-water ice will not be underestmiated, a rather 

 larger average size has been allowed for the bergs than would otherwise 

 be the case. 



It is quite likely that a fair estimate of the correct annual total 

 amount of above-water glacial ice that enters the region about the 

 Grand Banks will be obtained by multiplying the total number of 

 bergs given by the ice patrol as south of the forty-eighth parallel 

 each year by 4,000,000 cubic feet. This figure is advanced as a 

 maximum one, the real amount being probably somewhat smaller,, 

 due mainly to duplication of berg reports. 



The total amount of ice to come south of the forty-eighth parallel is^ 

 of course, the sum of that which is above and below the sea surface. 

 The underwater body of a berg being quite irregular and largely 

 hidden, its total volume is extremely hard to determine by actual 

 observation or measurement. In the past it has undoubtedly been 

 overestimated. The fresh-water glacial ice of the North Atlantic 

 iceberg is, according to experiments made by the physicist, H. T. 

 Barnes, about 10 per cent lighter than the solid ice which is formed 

 on the surfaces of lakes and streams in winter. The reason for its 

 lightness is found in the much larger proportion of air in the form of 

 tiny bubbles that it contains. All the pictures of ice in this bulletin 

 show how white and clouded with innumerable tiny air bubbles the 

 glacial ice of icebergs really is. According to Barnes' estimate its 

 specific gravity averages close to 0.830 as compared with about 0.916 

 for clear ice and 1.000 for pure water at the point of maximum 

 density. 



Since nearly all of the bergs to the south of latitude 48° N. float in 

 sea water of density varying between 1.02 and 1.03, they must float 

 on the average about one-fifth out of water instead of one-eighth. 

 Until recently the latter figure has commonly been accepted a& 

 approximately correct, but if Barnes is right, it is entirely too small. 



