121 



Assuming that the sinking action attracts in toward the berg the 

 surrounding surface waters down to the 10-foot level, what wiU be 

 the rate of inflow of these surface layers? At the circumference of a 

 circle of 1,000-foot radius from the center of the waterline plane of 

 the berg the area of a 10-foot vertical section of the surface layers of 

 water will be 62,832 square feet. A horizontal inflow of but 27 feet 

 per day, which is only about 0.0002 knot, will more than suffice to> 

 supply 1,664,000 cubic feet of water daily through an opening of this 

 size. By proportion it can be assumed that the inflow will amount 

 to about 270 feet per day, or 0.002 knot, at a point close to the ice 

 walls, but 100 feet from the center of the waterline plane of the berg. 



The above figures are believed to give a very fair theoretical value 

 for the order of magnitude of surface inflow that is possible about a 

 berg melting in the Grand Banks region. The inflow is undoubtedly 

 so small in value that differential drift of surface and subsurface 

 layers, wind and wave effects, and other confusing elements, are 

 easily capable of distorting and entirely masking most of the notice- 

 able effects of such an inflow, if and when it exists. Even should the 

 above approximations be in error by a factor of 10, still the inflow 

 toward the most rapidly melting bergs would be extremely small. 



It is now" plain why growlers calved while breezes of any appre- 

 ciable strength are blowing generally float away rapidly to leeward 

 from a berg. Even those produced during periods of light airs and 

 calms almost invariably move away, though on the average at much 

 lower rates of speed. The maximum flow that the sinking of chilled 

 water can cause apparently produces an inflow of surface water so 

 small that it is nearly always masked by the other forces operating. 

 If the inflow were at all large it would often be able to hold calved 

 growlers and small pieces in positions alongside the parent berg. 



Final conclusions regarding the local circulation, both vertical and 

 horizontal, about bergs south of latitude 44° or 48° N. should not be 

 drawn from theoretical considerations, however. Neither should 

 they be formed from the results of a study of tank experiments or of 

 the few actual observations about bergs that have been made to date. 

 It is hoped that when opportunity offers the ice patrol will take 

 numerous special oceanographic stations and make studies with 

 variously colored stains placed in the water close to bergs during aU 

 sorts of weather and water conditions. What is now needed is a 

 larger body of exact observational data upon which to base sound 

 opinions. 



Microthermographs have been suggested as instruments for warn- 

 ing ships of the proximity of ice during times of low visibility, but 

 whether they will ever be of much practical value is stiU an open 

 question and subject to grave doubt. The scientific observer of the 

 international ice patrol should never be satisfied until after the detailed 

 100277—30 9 



