Ice in the Sea 275 



The destruction of icebergs proceeds by calving, melting and erosion. Icebergs 

 are often rapidly decreased in size by the breaking away of large and smaller pieces 

 of ice. This may change the equilibrium of an iceberg so that it capsizes or rolls over. 

 In cold water the melting process goes on mainly at the water line of icebergs (by 

 the formation of holes). Melting increases greatly when they drift into warm water 

 (e.g. south of the Newfoundland Banks in mixed water or in the warm Gulf Stream). 

 Destruction from above is due to melt water running down the sides of the iceberg, 

 by erosion and the action of the waves and rain. According to measurements made by 

 Drygalski in North-east Bay, an iceberg in the summer months may lose from 3 to 4 m 

 in 7 days. Between Greenland and Newfoundland the ice mass may decrease to an 

 eighth, corresponding to a daily loss of 1-8 m a day. In the same time the height 

 decreases by a half. 



{d) Iceberg Drift in the Arctic and Antarctic 



Icebergs in the open sea are subject to the eroding action of winds and currents. 

 These effects are dependent: (1) on the ratio of the masses of ice above and below the 

 water; (2) on the strength and duration of the wind; and (3) on the velocity and direc- 

 tion of the currents. Mecking (1906) has emphasized the great importance of the wind 

 and currents for iceberg drift in Baffin Bay. The coastal current plays the decisive part 

 and the wind determines the course of the icebergs only when this current is weak. 

 The continuous off-shore wind along the coast of western Greenland in the summer 

 thereby determines the number of icebergs reaching the Labrador current and thus 

 the number of icebergs off Newfoundland in the following spring. 



The International Ice Patrol Service, in order to determine the influence of the 

 factors mentioned above on the course of the icebergs, has followed the drift of a 

 large number in the area of the Newfoundland Banks and has recorded the meteoro- 

 logical and oceanographic conditions at the same time and Smith (1931) has discussed 

 this data in detail. The effect of the wind was made up of two parts: (1) the direct 

 force of the wind exerted on the exposed surface of the iceberg above the water; 

 and (2) the movement of the floating iceberg with the wind drift set up in the top layer 

 of the water. For the latter influence it must be kept in mind that for a steady state 

 the wind drift at the surface of the sea is deflected by 45° to the right of the wind 

 direction (Northern Hemisphere). This deflection increases with depth and a mean 

 deflection of 72° can be assumed for the upper 50 m. For the two cases of (a) deep- 

 immersing larger icebergs and (b) smaller icebergs with immersion ratios of 1 : 1 

 and 1 : 2 average conditions of the effects of these two forces are given in Table 107 

 (Fig. 126). 



The drift speed of larger, deeper-immersing icebergs with a deflection of 40° to 

 the right of the wind is less than that of smaller icebergs of lesser depth of immersion 

 for which the wind force and the force due to wind drift act more closely together. 

 In this case the deflection from the direction of the wind is only 20°. For more ac- 

 curate information on the distribution of icebergs in different parts of the sea it is 

 necessary to make a survey of the existing iceberg accumulations. The International 

 Ice Patrol Service carried out a systematic investigation of this type with the patrol 

 boat "Marion" and at the same time the research ship "Godthaab" (Riis Carstensen, 



