DISCUSSION OF ICEBERG AND ENVIRONMENTAL CONDITIONS 



1975 Season 



Despite annual fluctuations in iceberg produc- 

 tivity of the Greenland glaciers, sufficient bergs 

 are normally available in the west Greenland 

 inventory to produce a record iceberg year on the 

 Grand Banks, given the right environmental con- 

 ditions. Four factors or conditions primarily 

 determine the number of icebergs that will drift 

 toward and ultimately survive to reach the Grand 

 Banks. These are the intensity or volume trans- 

 port rate of the Labrador Current ; the direction, 

 magnitude and duration of the prevailing winds 

 encountered by the icebergs during this drift; 

 the extent of the sea ice cover available to protect 

 the icebergs; and, finally, the environmental con- 

 ditions to which the iceberg is exposed when out 

 of sea ice (i.e., air and water temperatures, wave 

 action). Abnormalities in any of these could be 

 responsible for either a very light or heavy ice- 

 berg season off Newfoundland. 



The 1975 iceberg season saw only 101 icebergs 

 cross 48°N latitude. This was less than one third 

 of the 1946 to 1974 average. Why did so few 

 icebergs reach the Grand Banks during 1975? 

 The following paragraphs provide a discussion 

 of the 1975 iceberg and environmental conditions 

 in an attempt to answer this question. 



This season's sea ice cover is discussed in the 

 Ice Conditions section. Features of the Labrador 

 and North Atlantic Current observed during 

 1975 are reviewed in the Oceanographic Condi- 

 tions section of this publication. 



The first indication that the season would 

 probably be lighter than normal came with the 

 January preseason mission. During these flights, 

 only 336 icebergs were sighted, one third the 

 1963-1974 average (See Figure 2). During the 

 February preseason flights, 518 icebergs were ob- 

 served south of 67°N latitude. This was again 

 about one third the average, but only one quarter 

 the number normally encountered between 62°N 

 and 67°N latitude during late February (See 

 Figure 4). The track lines for both of these 



surveys were selected to cover those areas where 

 the larger icebergs, under the influence of favor- 

 able environmental conditions, would be in a 

 position to reach the Grand Banks. The low 

 numbers of icebergs encountered during these 

 surveys were believed to be due primarily to two 

 conditions. First, Baffin Bay was essentially free 

 of sea ice for most of two months and the west 

 coast of Greenland south of 75°N was free of sea 

 ice from mid-July until early November. This 

 was some two or three weeks longer than normal, 

 during which time the icebergs were exposed to 

 open water. Secondly, a deeper than normal 

 Icelandic low during the late fall created higher 

 winds and thus more turbulent seas off the middle 

 west Greenland coast. These factors combined 

 to accelerate the deterioration rate of icebergs in 

 this area. Certainly, the fact that the last three 

 seasons had brought record numbers of icebergs 

 to the Grand Banks had some effect on the ice- 

 bergs in a position to drift south during 1975. 

 Although, as always, large numbers of icebergs 

 were available in the west Greenland inventory, 

 it is believed that fewer were near or in the pri- 

 mary ocean currents carrying icebergs on their 

 long trek to the Grand Banks. 



Figures 25a through 25e show the normal and 

 1975 surface pressure patterns for November 

 through August. The isobars, shown as heavy 

 solid lines in these figures, provide an indication 

 of average wind direction in any particular area. 

 Winds tend to blow in a direction nearly parallel 

 to the isobars, counterclockwise around a low 

 pressure area and clockwise around a high for 

 the Northern Hemisphere. 



The predominant characteristics of the average 

 pressure patterns from November through March 

 was the abnormally intense Icelandic low pro- 

 ducing stronger than normal northerly and north- 

 westerly winds south of Davis Strait along the 

 Baffin Island and Labrador coasts. The resultant 

 flow brought the icebergs south much faster than 



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