ICE OBSERVATION 



The varying ice conditions that existed during the first nine months 

 of 1929 in the North Atlantic south of the forty-eighth parallel are dis- 

 cussed here. The monthly ice charts (figs. 6-1 1 inclusive) show plainly 

 where the ice at different times was located with respect to the coast 

 lines, principal steamship tracks, and other features of the Grand 

 Banks region. They furnish a far better means than written re- 

 marks for comparing the change of ice conditions from month to 

 month and those of certain months of one year with corresponding 

 months of another. United States Hydrographic Office Miscellane- 

 ous Chart 2,511 was used as the base map for plotting all ice data. 



Iceberg totals and ice conditions are based during the actual active 

 patrol season on first-hand information, supplemented by that re- 

 ceived by radio from ship and coast stations. Reports of ice published 

 weekly in the United States Hydrographic Bulletin and those received 

 from Canadian Government authorities are depended upon during 

 the inactive season when there is no patrol ship in the vicinity of the 

 Grand Banks. 



The large number of ships on the various tracks that cooperate by 

 reporting regularly makes much care necessary to keep duplications 

 from unduly swelling the berg totals. Suppose, for instance, that 10 

 ships all pass along the same general line and each one reports four 

 bergs to the patrol from about the same locations on the same day. 

 Only one of these reports of ice can be considered for broadcast and 

 statistical purposes, for it is obvious that all the ships have seen and 

 reported the same ice. 



Probable drift tracks of ice are rather well known from experience, 

 and the general principles of these drifts are explained in conjunction 

 with the charts on pages 68 and 69 of the Ice Patrol's Bulletin for 1927. 

 In addition, particular detailed drifts and variations from the general 

 .rules can often be forecast after a study of the cruise isotherm and ice 

 charts that are always kept up to date on the patrol vessels. Bergs 

 reported from one position on one day, therefore, are frequently 

 .assumed to be identical with bergs reported from two or three and 

 sometimes even five or six days earlier from different locations, and 

 are eliminated from the statistical totals. But no reported berg is 

 omitted from the broadcasts unless it is pretty definitely known to 

 be identical with some other reported berg. It is certainly wiser 

 to broadcast the presence of slightly more ice than exists rather than 

 .to eliminate from the reports mention of any ice that may still remain. 



(75) 



