Evaluation of bergy bit populations on the Grand Banks

Shuttle tankers and hydrocarbon production platforms operating on the Grand Banks of Newfoundland must be designed for some level of ice loading. In some cases, high ice loads can result from relatively small icebergs, bergy bits, or growlers. This is particularly true when wave-induced ice motions are significant (in high sea states) or when vessel speeds are high (e.g., a transiting tanker).Safe and economic operations can be achieved by designing structures that are strong enough to withstand ice loads, planning for and managing ice to reduce the risk of collisions, or a combination of the two. In all cases, accurate information on the number of small ice masses is important. Unfortunately, reliable information on small ice mass populations is not available. The extensive, detailed aerial surveys that would be required to build up meaningful statistics on bergy bit populations would be prohibitively expensive, and other methods of estimating bergy bit populations are required for the development of a reliable database.The approach used in this study was a reanalysis of International Ice Patrol (IIP) operational iceberg observations. Although the IIP does not detect and report all bergy bits and growlers, their database contains critical information on the location of small ice masses in relation to the aircraft track, and the prevailing visibility and sea-state conditions. By resampling only those ice masses observed when detection conditions were favourable, and within a prescribed distance from the aircraft, more accurate bergy bit statistics have been determined.A convenient measure of the number of bergy bits and growlers is the ‘small ice mass to parent iceberg’ (SIMPI) ratio. This relates the number of small glacial ice masses to the number of parent icebergs from which most small ice masses are calved. The average SIMPI ratio for the study region was 0.59. Some interesting phenomena revealed in the study include the apparent geographical variation in the small ice mass to parent iceberg ratio, with increasing values to the north and west. The ratio also varied seasonally. Of the months in which sufficiently large numbers of icebergs were observed to produce meaningful statistics, the SIMPI ratio was lowest in March (0.25) and highest in May (0.81).