Long Term Trends in the Iceberg Threat to the Northwest Atlantic 



In order to analyze the long term trend of the iceberg threat, 

 nineteen year running average iceberg counts were computed for the 

 years 1889-1960. The effect of the nineteen year running average 

 is to remove short term variations in the iceberg record. The 

 choice of 19 years for the period of the running averages was 

 arbitrary; it being desired to show trends which were only significant 

 over periods of about twenty years since that was the approximate 

 periods of the data series in Table 2. The nineteen year running 

 average of iceberg counts is shown in Figure 4. There appear to be 

 three phases in the data. The first phase, extending from 1889 to 

 the early 1920' s, was a more or less stable period with average 

 counts running between 325 and 440. The second phase, from the early 

 1920 's to about 1937, was a period when the average niunber of icebergs 

 was rising to almost 500. During the third phase subsequent to about 

 1937 the average iceberg count has fallen sharply and almost continously 

 to reach a low of about 200 as of 1960. Comparison of the stable, 

 rising, and declining phases with the criteria in Table 2 indicates 

 that the differences in the three phases are probably significant. 

 Assuming that the trends in Figure 4 are significant, then the average 

 iceberg danger at present is about half of what it was at the time of 

 the sinking of the Titanic in 1912, and is about 45% of what it was 

 in 1937. 



Factors Associated with Iceberg Trends 



The purpose of this paper is simply to present the long term trend 

 of iceberg statistics. The purpose is not, at this time, to explain 

 the causes of these trends. Presented below is information on long 

 term trends of environmental data that might be expected to be 

 associated with long term iceberg trends. The fact that the data 

 correlates is merely to be interpreted that the iceberg statistics 

 are probably valid. The choice of environmental data is severely 

 limited to that which is. available back to 1880. 



Soule, et al (1950) indicate that the three most important factors 

 affecting the iceberg threat are 1) the supply of icebergs available, 



2) the efficiency of iceberg transport to the northwest Atlantic, and 



3) iceberg mortality during the drift south. The complexity of these 

 factors is increased because they are interrelated and act over a 

 path of about 1800 miles and possibly several years duration. 



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