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7. Absence of swell or motion of the water in a fresh breeze is a 

 good sign of ice to windward, if the vessel is not in the vicinity of 

 land. 



8. Lowering of the temperature of the surface layer of sea water, 

 or the lowering of the air temperature, may indicate that the ship 

 has entered waters where ice is likely to be encountered. The con- 

 verse does not apply ; nor should maintenance of sea and air tempera- 

 tures be taken to mean that no ice is about, 



9. The presence of walruses, seals, or birds may indicate the prox- 

 imity of the ice, if far from land. The Antarctic petrel is normally 

 seen only within about 400 miles of the ice edge. The appearance 

 of the snow petrel is an almost certain indication that pack ice is 

 within a few hours' steaming. 



SIGNS OF OPEN WATER 



1. Dark patches on low clouds, sometimes almost black in compari- 

 son with the clouds in general, indicate the presence below them of 

 open water. This is known as water sky. Like iceblink, this phe- 

 nomenon depends on the greater absorption of sunlight by water 

 than by ice or snow, and the subsequent diffusion of the reflected light 

 in the lower atmosphere. When the air is very clear, it tends to be 

 suppressed. 



2. Dark spots in fog give a similar indication, but are not visible 

 for as great distances as reflections on clouds. 



3. A dark band on a cloud at a high altitude indicates the existence 

 below this line of small patches of open water which may connect with 

 a larger distant area of open water. 



4. The sound of a surge in the ice indicates the presence of large 

 expanses of open water in the immediate vicinity. 



The best weather conditions for navigating in the ice are fine days 

 with a clear horizon and atmosphere, but with the sky covered with 

 an even layer of clouds. Then, as stated previously, the iceblink ap- 

 pears in light markings on the under surface of the clouds above it. 

 AVliere leads of open water occur in the pack, the iceblink is sharply 

 broken, with water sky appearing almost black by contrast. 



If when approaching ice there is darkness on the horizon beyond a 

 light sky, it indicates that there is open water or land beyond the ice, 

 in some cases 40 miles or more beyond the visible horizon. If thin, 

 dark streaks on the sky are observed, the existence of leads is indicated. 

 If there are no dark streaks, a vessel should steer for the place where 

 the iceblink is dullest. The clarity of the blink is increased after a 



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