ON THE DETERIORATION OF ICEBERGS IN THE MARGINAL ICE-ZONE

During the Labrador ke Margin Experiment (LIMEX) of March-April 1989, the International Ice Patrol (IIP) of the United States Coast Guard deployed two satellite-tracked TIROS Arctic Drifter (TAD) platforms on two medium-sized tabular icebergs. The icebergs were drifting in sea ice of about 9/10 concentration east of Newfoundland. These deployments were part of an experiment to examine differential sea-ice/iceberg motion during spring conditions near the ice margin. Sea-ice concentration and movement data were collected concurrently by other LIMEX investigators. The TADs, deployed on 11 March 1989, were tracked using the ARGOS data collection and location system carried on two NOAA polar-orbiting satellites of the TIROS family. For two months following the deployment, IIP periodically attempted to relocate the icebergs during routine aerial iceberg patrols. One of the TADs stopped transmitting on 23 April 1989 probably because of a major calving event that resulted in the TAD being crushed. As of 24 April the drift rate of the other TAD nearly doubled compared with its drift rate prior to that date, indicating that it had fallen off the iceberg and was floating on water. By 24 April there was no sea ice near either of the two icebergs. The TAD data provide a unique dataset for modelling the deterioration of icebergs while they emerge out of the marginal ice zone and travel in open water. It is shown that a good knowledge of the environmental conditions, particularly water temperature and sea state, are critical to model successfully the deterioration and calving of the two icebergs.