DISCUSSION OF ICEBERG AND ENVIRONMENTAL CONDITIONS 



1976 SEASON 



The 1976 season was the second light season 

 in a row, with only an estimated 151 icebergs 

 crossing 48°N. This is less than half the 1946- 

 1975 average of 315 bergs. In attempting to 

 explain why this was a relatively mild season, 

 several environmental factors must be considered. 

 These include the number of bergs available to 

 drift across 48°N, the strength, duration and 

 direction of the winds that affect southerly ice- 

 berg drift, the sea ice cover that protected the 

 bergs from melt, the strength and position of 

 the Labrador current (discussed in the Oeeano- 

 graphic Conditions Section), and finally the 

 various parameters which determine the deteriora- 

 tion rate of icebergs. 



During the January Preseason flights, a total 

 of 563 bergs were sighted between 53° N and 71 °N 

 as shown in Figure 1. The January flights were 

 flown as far north as Cape Christian on Baffin 

 Island to ensure a total census of the area. The 

 late February /early March Preseason revealed 

 only 303 icebergs south of Cape Dyer with no 

 bergs below 48 °N, Figure 4. This was far be- 

 low statistical normals and lead to the expecta- 

 tion of another light season. Figures 30a through 

 301 show normal and 1976 surface pressure pat- 

 terns for November through August. The isobars, 

 shown as heavy solid lines, provide an indica- 

 tion of average wind direction for a given month 

 in our area of concern. Winds tend to blow 

 nearly parallel to the isobars, counterclockwise 

 for a low and clockwise for a high in the 

 Northern Hemisphere. 



During the earl}' part of the season, approxi- 

 mately November through mid-April, the pre- 

 dominant map feature was an abnormally posi- 

 tioned and unusually intense Icelandic Low. 

 This deviation produced strong to moderate sur- 

 face winds from the west and west-northwest 

 south of 52°N. With these winds and the result- 

 ing wind-driven currents, bergs approaching the 

 Grand Banks were driven to the east out of the 



core of the Labrador Current. This essentially 

 ended any further southward drift of this ice 

 and scattered the bergs eastward around the 

 Flemish Cap. 



The low upstream iceberg inventory and off- 

 shore winds were the main reasons for the below 

 normal counts of icebergs crossing 48°N in April. 



During May, the Icelandic Low appeared much 

 more intense than normal and was centered north- 

 northeast of its usual position. This caused the 

 prevailing winds to shift, coming from the north- 

 west, and by late May bergs were again drifting 

 south in the Labrador Current along the eastern 

 slope of the Grand Banks. 



As has been normal, average winds were on- 

 shore during June and for the remainder of the 

 season, inhibiting any further iceberg drift onto 

 the Grand Banks. 



Surface pressure gradients (differences in at- 

 mospheric pressure along a geographically ori- 

 ented line) provide an indication of wind 

 velocities that exist in the area. The steeper the 

 gradients, or the more rapid pressure change, 

 the higher the wind speed will be. In an attempt 

 to understand the magnitude and primary direc- 

 tion of winds along the main routes of icebergs 

 heading toward the Grand Banks, six such gra- 

 dients have been defined by Ice Patrol for Davis 

 Strait and certain areas off the Newfoundland 

 and Labrador coasts (Figure 31). From an 

 analysis of these gradients, inferences can be 

 made about the northwesterly winds producing 

 southerly iceberg drift, accentuating the Labrador 

 Current, reducing the air and sea temperatures 

 and developing and spreading sea ice along the 

 coasts of Labrador and Newfoundland. 



Gradients assigned numbers 1 and 2 in Figure 

 31 indicate the intensity of the north/south com- 

 ponents of the winds off the Labrador coast. 

 These winds are important in assisting or imped- 

 ing the drift of icebergs toward the Grand Banks. 



42 



