amount of traffic, it is sensitive to 

 the marine traffic patterns in the 

 IIP region. Throughout the 

 iceberg season, typically March 

 through June, ship traffic passes 

 through the area south of the 

 Grand Banks between latitudes 

 48°Nand440N. Late in the 

 season, when the Straits of Belle 

 Isle become ice-free, a large 

 amount of traffic transits the 

 northern part of the International 

 Ice Patrol area, north of 50°N. 

 This paper assumes that this 

 traffic pattern does not vary widely 

 from year to year and gives a 

 consistent annual sample of the 

 iceberg population in the IIP area. 

 The number of icebergs 

 encountered by ships in the 

 southern traffic lanes is assumed 

 to have a direct relationship to the 

 numberof icebergs south of 

 48°N that year, dependent on 

 the amount of traffic. It is further 

 assumed that the number of 

 icebergs sighted and reported by 

 ships in the northern traffic lanes 

 is related to the number of 

 icebergs passing south of 48°N 

 and that this relationship does not 

 vary widely from year to year. 

 These assumptions regarding the 

 relationship of iceberg sightings 

 to the number of icebergs south 

 of 48°N have two weaknesses. 

 First, during especially light or 

 heavy iceberg years, the normal 

 traffic pattern is disturbed. 

 Presumably, even though 

 shipping tracks may be displaced 

 to the north or south during these 

 years, the relationship between 

 iceberg density and the 

 probability of iceberg sighting by 

 individual ships should not be 



Table C-1 Icebergs South of 48°N: 



South of 48° N 



Icebergs 

 Year Est. 



1960 

 1961 

 1962 

 1963 

 1964 

 1965 

 1966 

 1967 

 1968 

 1969 

 1970 

 1971 



253 



117 



120 



25 



369 



76 







441 



226 



57 



85 



73 



Sightings, 

 All Sources 



1538 

 1286 

 1072 



163 

 3712 



277 



13 

 1448 



719 



171 



324 



222 



Ratio 



i^t XI 00) 

 Sighting 



16.4 



9.1 

 11.2 

 15.3 



9.9 

 27.4 



0.0 

 30.5 

 31.4 

 33.3 

 26.2 

 32.9 



Year 



1972 

 1973 

 1974 

 1975 

 1976 

 1977 

 1978 

 1979 

 1980 

 1981 

 1982 

 1983 

 1984 



Estimated vs Sightings 



South of 48°N Ratio 



Icebergs Sightings, (Est x^qq> 

 Est. All Sources sighting 



1548 



850 



682 



101 



151 



22 



75 



152 



24 



63 



188 



1348 



2202 



3978 



2980 



3355 



331 



454 



84 



341 



168 



3 



26 



70 



620 



1106 



39.8 



28.5 



20.3 



30.5 



33.3 



26.2 



22.0 



90.5 



800.0 



242.3 



268.6 



217.4 



198.3 



greatly affected, since ships will 

 tend to travel through waters of 

 "normal" (i.e., low) iceberg 

 density even in abnormal years. 

 Second, as icebergs drift south 

 from the northern lanes, they are 

 subject to varying environmental 

 conditions (sea surface 

 temperatures, wave heights, 

 winds and currents) that affect 

 iceberg deterioration and 

 transport. The fraction of the 

 icebergs sighted in the northern 

 lanes that eventually reach 48°N 

 varies with these changing 

 environmental conditions. 

 However, since these 

 environmental conditions usually 

 follow predictable seasonal 

 patterns and long-term variations 

 from seasonal norms (e.g., 1972 



and 1966) are rare, it is 

 reasonable to assume that the 

 relationship between the number 

 of sightings in the northern lanes 

 and the number of icebergs 

 south of 48°N does not vary 

 widely. 



Table C-2 contains totals of 

 ship iceberg and SST reports, 

 numbers of sightings south of 

 48°N from the International Ice 

 Patrol historical data file (which 

 contains information for 1960 

 through 1984), and the 

 computed iceberg sighting ratio 

 for each year. It is important to 

 point out that ships often report 

 more than one iceberg sighting 

 on a single report. The term "ship 

 iceberg reports" in Table C-2 

 represents the total number of 



71 



