ICEBERG POPULATION SEVERITY 



Almost all authors using IIP data have 

 struggled with the non-normal distribution of 

 the population data. Figure 2 shows the fre- 

 quency distribution of the iceberg populations 

 for the entire record and the SLAR years. In 

 both cases, low populations are the most 

 frequent. Table 2 illustrates this point numeri- 

 cally. In both cases, the median is much lower 

 than the mean. Thus, the average fails to 

 emphasize that the iceberg intensity is most 

 commonly very light. In addition, the standard 

 deviation for the SLAR years is so large that 

 only two data point can be considered statisti- 

 cally greater than the mean. In other words, 

 only two data points can be considered "larger 

 than average". Therefore, these averages are 

 meaningless and comparisonsto them should 

 be avoided. 



Many authors (Smith (1 931 ), Marko, et 

 al. (1986), Marko et al. (1994)) have shown 

 that sea-ice is a more reliable iceberg popula- 

 tion predictor than other environmental in- 

 dexes (e.g., air temperature, zonal pressure 

 difference). Marko, et al. (1 994) found a good 

 correlation between the iceberg count and the 

 Grand Banks sea-ice extent. Intriguingly, 

 they also showed a bilinear response of the 

 iceberg count to the sea-ice extent. In other 

 words, low and high sea-ice years had a 

 differing relationship iceberg count to ice ex- 

 tent. The threshold value for the different 

 responses was associated with an ice extent 

 that placed the outer edge of the ice edge over 

 the core of the Labrador Current. In other 

 words, when the sea-ice limits cover the core 

 of the Labrador Current, iceberg counts in- 

 crease markedly per unit increase in sea-ice 

 cover. Based on his iceberg-sea ice scatter 



Table 2 

 Mean and Median Iceberg Population Count 



-Tables 

 Marko, et al. (1994) Iceberg Population 

 Severity Classes 



Low 



Intermidiate 



High 



t; 



<200 icebergs south of 48°N 

 200-600 icebergs south of 48°N 

 >600 icebergs south of 48°N 



■^ 



50 



