APPENDIX C 



ICEBERG POPULATIONS SOUTH OF 48°N SINCE 1900 



by Lieutenant H. Gregory KETCHEN, USCG 



International Ice Patrol has traditionally 

 maintained counts of the number of icebergs 

 crossing latitude 48° North. Icebergs south of 

 this latitude are at best a potential and at worst 

 a real hazard to the safety of primary North 

 Atlantic shipping. 



Table C-l provides a breakdown by month of 

 the. estimated number of bergs crossing 48 °N 

 since 1900. This is an update of and provides 

 some corrections to the table last published in the 

 1968 Ice Patrol Bulletin No. 54. The counts are 

 broken down into two groups, 1900 through 1977 

 and 1946 through 1977. This separation is done 

 because after World War II, aircraft recon- 

 naissance became the primary method used by 

 IIP for locating and tracking icebergs. Prior to 

 that time, iceberg distributions were determined 

 from surface observations made from Coast 

 Guard cutters patrolling the southern limit of 

 icebergs plus sightings by merchant and fishing 

 vessels transiting the area. Since aerial coverage 

 proved to be much more complete and frequent, 

 data collected subsequent to 1945 represent more 

 accurate counts. 



Figure C-l is a bar graph of the estimated 

 numbers of icebergs crossing 48 °N during each 

 year since 1900. The variability in the record is 

 obvious, with counts ranging from bergs in 

 1966 to 1,587 in 1972. Monthly average counts 

 for the full record and for recent years are de- 

 picted in figure C-2. Although a good indicator 

 of relative importance of a particular month, 

 those averages are biased by the high counts of a 

 few extremely severe years. A better figure for 

 the number of icebergs that might be expected 

 to cross 48°N in a "typical" year is provided by 

 the median of the counts. For the period 190*0 

 through 1977 the median of the annual iceberg 

 counts is 279, while the average is 383. For the 

 period 1946 through 1977, the corresponding 

 median is 107 while the average is 300. 



Further analysis of the variability of iceberg 

 distributions is provided in an article by C. W. 

 Morgan titled "Long Term Trends in the Iceberg 

 Threat in the Northwest Atlantic" published in 

 the 1971 Ic« Patrol Bulletin No. 57. 



C-l 



