except to say that fast ice becomes a very important factor as does 

 the timing of the f reezeup and the breakup of pack ice there. 



The fact that the movement of bergs embraced by the pack ice is 

 subject to the movement of the pack ice for considerable portions of the 

 crop's journey from glacier to Grand Banks has already been stated. 

 If this is true it behooves us to learn more about the forces that cause 

 sea ice to move. The two main forces are the Baffinland-Labrador 

 Current system and surface wind. The force of the current system is 

 self-explanatory. The pack ice, without any wind, will be carried 

 with the velocity of the surface current unless obstructed by fast ice 

 alongshore or pack ice jams downstream. The movement of bergs in 

 the current system is more complex, as the surface current and depth 

 current acting near the base of the berg may have different values. 

 Without wind, bergs will move at the average current velocity from 

 surface to berg depth unless obstructed by pack ice or bottom topog- 

 raphy or unless pushed and carried by the pack ice. Existing wind 

 will exert a pressure on pack ice depending mainly on its roughness, 

 amount of ridging and hummocking, all of which tend to increase the 

 pressure due to wind and consequently drift due to wind. Water will 

 offer some resistance to the motion depending upon the speed. While 

 bergs embraced by close pack heavy ice generally are subject to pres- 

 sures from the pack ice and move accordingly, those bergs with con- 

 siderable sail area probably transfer pressure to the pack ice and move 

 it faster during windy periods. On the other hand, the underwater 

 portion of a berg must create considerable resistance due to motion 

 relative to the water. 



In conclusion, sea ice does affect berg movement significantly and 

 is a factor that must be considered to properly evaluate the drift of 

 bergs due to atmospheric pressure patterns. The sea ice influence on 

 berg drift is very difficult to assess and properly evaluate. It is con- 

 cluded that onshore winds generally are more effective in moving 

 sea ice and bergs out of the Baffinland-Labrador Current system axis 

 than are offshore winds. It is assumed to be difficult for a significant 

 portion of the crop to be eliminated from the current system by being 

 driven out to sea as the generation of wind driven currents is impeded 

 by the sea ice. However, during the later part of the ice season as 

 the pack ice deteriorates and the limits recede northwestward, off- 

 shore winds in the Notre Dame-Belle Isle area can be most effective 

 in eliminating most of the second half of the crop. Generally, onshore 

 winds of sufficient strength will be assumed to have grounded most of 

 the berg concentrations unless observed ice conditions indicate other- 

 wise. Systematic northern ice surveys for the months preceding the 

 Grand Banks ice season will permit observation of sea ice conditions, 

 enable intelligent estimates of sea ice conditions, and thus allow a 

 more knowledgeable evaluation on the effect of sea ice. 



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