DISCUSSION OF ICEBERG AND ENVIRONMENTAL CONDITIONS 

 DURING 1970 SEASON 



Tlie question of how and why the iceberg sea- 

 son develops as it does is always of interest to 

 the Ice Patrol. This is particularly true when the 

 season does not develop as expected, as happened 

 in 1970. The three major factors which influence 

 the development of the season are (1) the num- 

 ber of icebergs available to drift onto the Grand 

 Banks, (2) the strength of the northwesterly 

 winds which transport the icebergs south, and 

 (3) the rate of deterioration the icebergs experi- 

 ence due to melting and wave action. In early 

 March, as described in the section on ice condi- 

 tions, there were 95% more icebergs present north 

 of Hamilton Inlet than normal. Therefore the 

 potential for a heavy iceberg season was present, 

 and it was the factors which influence iceberg 

 drift and deterioration which led to a light 

 season. 



The features of the Labrador Current, as de- 

 scribed in figures 14-17, appear suiRciently well 

 developed to play their usual role in transporting 

 icebergs along the eastern slopes of the Grand 

 Banks. The recur vature of isotachs at about 45N 

 to 46N on all four surveys indicates that some 

 icebergs in the Labrador Current would be un- 

 able to drift south of about 45N or 4:6N. In fact 

 the southernmost iceberg of the season was lo- 

 cated at about 45-35N in the southern part of 

 the eddy indicated by the 970.9 dynamic meter 

 isotach on figure 17. At the end of the second 

 cruise there does not appear to be any significant 

 eastward branching of the Labrador Current be- 

 tween the northeast slope of the Grand Banks 

 and Flemish Cap ; however this could occur later. 



Sea surface temperatures on the northeast 

 slopes of the Grand Banks, as revealed by com- 

 parison of sea surface temperature charts from 

 Fleet Weather Central Norfolk with normal sea 

 surface charts given in Report of the Interna- 

 tional Ice Patrol in the North Atlantic, Season 

 of 1964, appeared to be about a degree Fahren- 

 heit or more warmer than average from late 

 April through at least early June. This probably 



had some effect in hastening the melting of ice- 

 bergs. 



Figures 18a through 18d show the normal and 

 the 1969/1970 surface atmospheric pressure pat- 

 terns for November through June. Pressure pat- 

 terns through January do not appear as if they 

 would impede the southward drift of icebergs to 

 any unusually great degree. This, in connection 

 with the above normal iceberg counts noted in 

 December and in the fall, probably accounts for 

 the higher than average iceberg count along the 

 Labrador coast in February. In March there is 

 a splitting of the Icelandic low, with a secondary 

 low forming over Newfoundland. The average 

 cyclonic circulation associated with this low 

 would have been unfavorable to any strong east- 

 ward drift of icebergs from the area of Belle Isle 

 Strait or north. The average pressure pattern for 

 April shows that the secondary low still exists, 

 however it is now centered slightly to the east 

 of Newfoundland. In this position winds would 

 continue to be generally unfavorable for the drift 

 of icebergs along the eastern slopes of the Grand 

 Banks, however the winds would not generally 

 oppose the drift of icebergs along the Avalon 

 Peninsula. In fact the five icebergs that did drift 

 south of 48N in April all did so to the west of 

 50° west longitude. During May the secondary 

 low near Newfoundland disappeared and a fairly 

 intense Icelandic low was established. This re- 

 sulted in winds with a westerly component pre- 

 dominating in the coastal areas of Newfoundland 

 and southern Labrador. These average westerly 

 winds continued through June. 



As a more quantitative indicator of the wind, 

 one may examine the difference in atmospheric 

 pressure along a line as a measure of the average 

 wind perpendicular to the line. Four such lines 

 are labeled gradients 1 through 4 in figure 19. 

 Gradients 1 and 2 measure the winds which are 

 important in transporting icebergs to the general 

 area of the waters off northeast Newfoundland. 

 Gradient 3 is a measure of the winds which 



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