Appendix C 



International Ice Patrol's Iceberg Season Severity 



Geoffrey Trivers 



INTRODUCTION 



Throughout its history, International Ice 

 Patrol (and other authors) has struggled to 

 define an "average" iceberg season. Despite 

 the many different possible iceberg-season 

 severity indexes (iceberg population, iceberg 

 season length, iceberg-limit area! extent), the 

 only Ice Patrol index has been iceberg popu- 

 lations south of 48°N. 



Most recently, Alfultis (1987) defined 

 four population severity classes (Table 1) 

 based on the entire iceberg record (1900- 

 1 987). However, recognizing the various ice- 

 berg data collection methods. Ice Patrol An- 

 nual Reports have also compared the respec- 

 tive year's iceberg population to averages for 

 the different data collection years (e.g., 1 945- 

 1 982: aircraftyears,1982-present: Side-Look- 

 ing Airborne Radar (SLAR)-equipped aircraft 

 years). The recent sole use of the SLAR- 

 years' average implies that the SLAR years' 



data is more trustworthy than the pre-SLAR 

 years' data, a seemingly reasonable assump- 

 tion, though tough to quantify. (See Anderson 

 (1993) for an excellent synopsis of the impact 

 of changing Ice Patrol technology on the ice- 

 berg counts.) 



However, one shouldn't blindly make 

 conclusions on a record as short as the SLAR 

 years. An extreme year under the Alfultis 

 (1 987) definition is "average" according to the 

 SLAR-years mean (Table 2). Is this evidence 

 that the pre-SLAR-years population data is 

 undercounted? Or does this mean that the 

 SLAR-years populations are overcounted? 



This paper examines the iceberg popu- 

 lation data (Figure 1 ) against high quality sea- 

 ice data in order to redefine the severity defi- 

 nitions and also examines another potential 

 severity index, iceberg season length. 



Table 1 

 Alfultis (1987) Iceberg Population Severity 



Classes 



Light 



Average or Intermediate 



Heavy 



Extreme 



t: 



<300 icebergs south of 48*1^1 

 300-600 icebergs south of 48°N 

 601-900 icebergs south of 48°N 

 >900 icebergs south of 48°N 



■^ 



49 



