Appendix B 



Iceberg Populations South of 48° N Since 1900 



LT Michael A. Alfultis, USCG 



Since its beginning, the 

 International Ice Patrol has 

 maintained an annual count ot 

 the number ot icebergs cross- 

 ing latitude 48°N. Each year 

 the number ot icebergs south of 

 48°N is used by International 

 Ice Patrol to gauge the potential 

 threat to North Atlantic ship- 

 ping, and, therefore, the 

 opening and closing date of each 

 Ice Patrol Season. 



Table B-1 provides a 

 monthly breakdown of the 

 estimated number of icebergs 

 crossing 48°N each year since 

 1900. This updates the his- 

 torical iceberg statistics last 

 published in the 1977 Ice 

 Patrol Bulletin No. 63. Table 

 B-1 is in a slightly different 

 format from that published 

 previously. Recently, Interna- 

 tional Ice Patrol began using as 

 its ice year the period from 

 October through September 

 rather than the calendar year 

 or the period September 

 through August, as was done in 

 the past. The data published in 

 1977 have been updated to 

 reflect this, and the iceberg 

 counts since 1977 added. 



The monthly counts are 

 broken into four eras, 1900- 

 1912, 1913-1945, 1946- 

 1982, and 1983-1987. The 

 first era is the pre-lnterna- 

 tional Ice Patrol period when 

 icebergs sighted by commercial 

 shipping were reported to the 

 U. S. Hydrograhic Office. 

 During the next era, the Inter- 

 national Ice Patrol estimated 

 the iceberg distribution from 

 surface observations made 

 from U. S. Coast Guard cutters 

 and commercial vessels tran- 

 siting the area. Visual recon- 

 naissance from aircraft became 

 International Ice Patrol's 

 primary method for iceberg 

 detection during the third era. 

 During the final era, the Side- 

 Looking Airborne Radar 

 (SLAR) provided International 

 Ice Patrol with an all-weather 

 capability to detect icebergs. 

 Iceberg sightings provided by 

 commercial shipping have 

 been, and continue to be, an 

 important source of informa- 

 tion to International Ice Patrol. 



International Ice 

 Patrol defines those ice years 

 with less than 300 icebergs 

 crossing 48°N as light or low 

 ice years; those years with 

 300 to 600 icebergs crossing 

 48°N as average or intermedi- 

 ate ice years; those years with 

 600 to 900 icebergs crossing 

 48 °N as heavy or severe ice 

 years; and those ice years with 

 more than 900 icebergs cross- 

 ing 48°N as extreme ice years. 



Figure B-1 is a bar 

 graph of icebergs crossing 48 

 N since 1912. The variability 

 in the record is readily seen. 

 The factors that determine this 

 variability are the supply of 

 icebergs available to drift onto 

 the Grand Banks, those affect- 

 ing iceberg transport (cur- 

 rents, winds, and sea ice), and 

 those affecting deterioration 

 (wave action, sea surface 

 temperature, and sea ice). 

 These factors are often unpre- 

 dictable. During the 1987 

 season, short term changes in 

 the mean wind flow dramati- 

 cally affected the iceberg 

 distribution, and changed the 

 character of an anticipated 

 severe iceberg season to barely 

 an average season (318 ice- 

 bergs). 



63 



