ICEBERG TAGGING AND DRIFT STUDY, INTERNATIONAL 

 ICE PATROL CRUISES 1974 



R. M. HAYES 1 



R. Q. ROBE 2 



R. W. SCOBIE 1 



ABSTRACT 



Iceberg tagging and drift experiments were 

 conducted near the Grand Banks of Newfoundland 

 in April and June 1974. Results of these 

 experiments, which were an attempt to tag 

 icebergs by encircling them with a floated line with 

 RDF transmitters for relocation and identification, 

 show that this method is not feasible. During 

 storms the line parted from both strain and 

 chafing. When weather was fair the iceberg would 

 work free of the line circle, probably by rolling over 

 or under the line and out of the circle. 



Average iceberg drift speeds vary from 10.3 

 cm/sec to 56.5 cm/sec. The average drift angle 

 with respect to the wind direction varies from 21° 

 to the left to 92° to the right. When in the high 

 velocity core of the Labrador Current, iceberg 

 drift is predominantly controlled by the current. In 

 the area of weak current, iceberg drift is deter- 

 mined by wind drag on the subaerial portion and by 

 water drag on the subsurface portion. The result- 

 ant drift of an iceberg with respect to the wind is 

 an important input to an iceberg drift model, and 

 experimental methods for predicting this wind 

 drift effect are discussed. 



INTRODUCTION 



During the 1974 Ice Patrol season the Coast 

 Guard Research and Development Center and the 

 Coast Guard Oceanographic Unit conducted an 

 iceberg drift project aboard the CGC 

 EVERGREEN. This project provided average 

 drift vectors for six icebergs in the Grand Banks of 

 Newfoundland area over a period of three to six 

 days. The results were forwarded to Commander, 

 International Ice Patrol (CUP). Comparisons were 

 then made by IIP between the observed drift 

 values and those predicted by computer model. 

 Icebergs were tagged to allow for the surveillance 



of a number of bergs distributed over an area of up 

 to 300 square miles. This also assured positive 

 identification upon subsequent visits to obtain posi- 

 tion fixes. In the past, attempts have been made to 

 mark icebergs using dye; however, iceberg 

 melting, rain, wave action, and iceberg rolling 

 often caused the dye patches to be washed away. 

 The complications of tagging a berg for future 

 recognition center around the dynamic nature of 

 an iceberg. 



Icebergs near the Grand Banks often deteriorate 

 rapidly. An iceberg's rate of decay is a function of 

 its environment and internal structure. Deteriora- 

 tion is hastened by warm sea and air temperatures, 

 as well as by rough seas. Rivulets of melting water 

 may be seen cascading down the sides of some 

 icebergs creating large channels on the surface and 

 often collecting in pools in the basin areas. Others 

 of the drydock variety have wave-cut embayments 

 which concentrate wave forces and speed 

 deterioration. Large chunks of ice often calve from 

 icebergs to accelerate their destruction. 

 Instabilities, which result from deterioration, 

 cause icebergs to pitch and yaw and in severe cases 

 to roll over completely. In consequence of these 

 dynamic changes, it has been very difficult to put 

 anything on, or attach any device to, an iceberg 

 that would remain in position long enough to give 

 positive identification over a significant time 

 interval (i.e., about 5-7 days). 



METHODS 



During the International Ice Patrol 1974 season 

 a method was tested for location redetermination 

 and differentiation of icebergs used in drift studies 



1 U.S. Coast Guard Oceanographic Unit, Bldg. 159-E, 

 Navy Yard Annex, Washington, D.C. 20593 



2 U.S. Coast Guard Research and Development Center, 

 Groton, Connecticut 06340 



