ICEBERG AND ENVIRONMENTAL 

 CONDITIONS 1977 SEASON 



There are several complex interrelated pa- 

 rameters which account for the numbers of ice- 

 bergs that will reach the Grand Banks during 

 an ice season. One of the least important of 

 e is fluctuations in the annual productivity 

 the west Greenland glaciers from which these 

 bergs originated. With an excess of 10,000 ice- 

 bergs calved each year from these glaciers, there 

 is certainly a sufficient iceberg inventory in 

 Baffiin Bay during any year to produce a severe 

 iceberg season in the vicinity of the Grand Banks. 

 There are four factors or conditions primarily 

 responsible for determining the number of ice- 

 bergs that will drift toward and ultimately sur- 

 vive to reach the Grand Banks. These are the 

 intensity or volume transport rate of the Labra- 

 dor Current ; the direction, magnitude and dura- 

 tion of the prevailing winds encountered by the 

 icebergs during their drift; the extent of the sea 

 ice cover available to protect the icebergs; and, 

 finally, the environmental conditions to which 

 the iceberg is exposed when out of sea ice (i.e., 

 air and water temperatures, wave action). Ab- 

 normalities in any of these could be responsible 

 for either a very light or heavy iceberg season off 

 Newfoundland. 



The 1977 Ice Season was one of the lightest 

 seasons on record with an estimated total of only 

 22 icebergs drifting south of 48°N. This was 

 significantly less than the 1946-1976 average of 

 300 icebergs and the median of 107. 



The sea ice observations during the 1977 Season 

 are discussed in the Ice Conditions section of this 

 publication. The. Oceanographic Conditions sec- 

 tion reviews features of the Labrador and North 

 Atlantic Currents as recorded by the Ice Patrol 

 research vessel EVERGREEN. Other environ- 

 mental parameters responsible for the scarcity 

 of icebergs in the vicinity of the North Atlantic 

 shipping lanes are discussed in the following 

 paragraphs. 



The January and Febiuary preseason surveys 

 as discussed in the Ice Conditions section re- 

 ferred to Figures 1 and 3, which gave the first 

 indications of a light season. The partial Jan- 

 uary survey and the nearly complete February 

 census found a relatively scarce population of 

 icebergs having the potential of reaching the 

 Grand Banks when compared with the normals 

 in Figures 2 and 4. 



Figures 19a through 191 depict the normal and 

 1977 sea surface pressure patterns for September 

 1976 through August 1977. When interpreting 

 the figures, the isobars, drawn as heavy solid 

 lines, provide an average wind direction. Winds 

 tend to blow nearly parallel with the isobars, 

 counterclockwise around low pressure and clock- 

 wise around high pressure cells in northern 

 latitudes. 



The predominant characteristic of the monthly 

 average sea surface pressures was the meandering 

 Icelandic Low. The October position of the Low 

 was located near its climatological mean but more 

 intense than normal. This Low began a westerly 

 drift during November and December across the 

 Labrador Sea, filling during December. Nearing 

 normal intensity, the Low was centered near 

 Belle Isle in January 1977. The resulting flow 

 patterns were southerly during October, slowly 

 shifting to the north-northeast for January. 

 This shift slowed the icebergs' southerly drift 

 and caused them to bunch between 65 °N and 

 70°N (Figure 1). 



During February, the Icelandic Low began to 

 deepen once more, slowly returning to its clima- 

 tological normal position for March while retain- 

 ing its intensity. The Low filled dramatically in 

 April and had drifted again to over the Labrador 

 Sea. During May, the Low intensified again and 

 continued to move to a position just north of 

 Notre Dame Bay, Newfoundland. The shift of 

 the Low released the icebergs previously retained 

 in January, and caused them to begin drifting 



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