H. ITO: What is the accuracy of the radar positioning system?
W. F. WEEKS: The accuracy appears to be roughly 0.5 m and would be expected to be largely independent of the length of the line surveyed.
ITO: How did you correct for tidal effects?
WEEKS: Tides in our study area are very small (≈0.25 m). Therefore we did not lake them into account.
ITO: What is the maximum range of the system?
WEEKS: The radar transponder system has a range of 80 km. However, because of the Earth’s curvature and the height of our towers, we were only able to range on targets that were within 37 km.
T. CARSTENS: There is a striking superficial similarity between the shear zones I have observed in lake “pack" ice originating from frazil, and the corresponding shear ridges along Arctic coasts such as the Alaskan Beaufort Sea coast. Do you feel that the analogy between this particular lake-ice process and the movement of Arctic pack can be made use of in a general model, in spite of the large differences in scale?
WEEKS: One undoubtedly can learn many useful things that are applicable to sea ice from the study of drifting lake or river ice. However, before we can begin to draw analogies with any sort of confidence, we need good observational data on all these ice types Therefore, I encourage you to collect any such data that you can obtain with the confidence that even if it does not prove to be directly applicable to sea ice it will ultimately prove to be useful in its own right.
P. R. KRY: The fact that absolute displacements increase with distance from the shore (or barrier islands) implies that perhaps the strain is constant; or that the fast ice may be considered to be a plate fixed at the shore. Is this reasonable?
WEEKS: The idea that the strain is roughly constant may prove to be correct. However, the fast ice does not act as a simple hinged rigid plate fixed at the shore inasmuch as the motions parallel to the shore are not particularly well correlated with each other.
K. R. CROASDALE: I am interested in your comments about the boundary of the fast ice. Could one define the edge of the fast ice to be where the lead opens up under the action of off-shore winds? If so, at what water depth was this? It may be of interest to note that off the Mackenzie Delta the edge of the fast ice follows the 20 m isobath fairly closely.
WEEKS: Some of the time there was quite a wide lead at the outer edge of the fast ice. At other times this lead was closed and the fast- and pack-ice areas were presumably separated by a zone of ridging. The boundary was commonly located at a water depth of 30-35 m.
J. W. GLEN: How do you reconcile your final recommendation that people with a sea-ice problem must go out to the site itself with Dr Weeks’ point in his review paper that sea-ice studies are usually best not conducted in the field?
WEEKS: It depends upon the type of problem. In the area of engineering properties one should do comprehensive sets of tests in the laboratory and determine how the state variables (temperature, composition, grain-size, etc.) influence the properties. Then all one need do in the field is roughly characterize the state variables and pick the correct property value off a graph. In other areas of interest such as ice drift we currently need good observational data. I see no way to predict from first principles or to model the sort of motions one might expect at the edge of a sheet of fast ice without first having observational data. Once we know what actually happens, then we can set out to develop models to explain and extrapolate our observations.
GLEN: Regarding your observations of ice motion; if it is not a strain phenomenon, is it a random-walk one ? There seemed to be less net motion than a square-root law would suggest, with some stations appearing to return home after their excursions. Was this fortuitous?
WEEKS: I believe that the return of the radar transponders to almost exactly their initial positions was largely fortuitous. This was, of course, favoured by the fact that the ice in the Beaufort Sea was tight, allowing very little motion.
L. W. GOLD: Has any progress been made in the development of a classification for sea ice?
WEEKS: The most detailed recent work on the overall structure of sea ice is by N. .V Cherepanov. However, he has not attempted a formal structural classification such as that of Ramseier and Michel for lake ice. I am not certain that it would prove profitable to propose such a classification until we know a bit more about what we are attempting to classify.