I don't know for a fact, but it would seem logical to use Greenwich Mean Time at or very near the poles. Isn't there a convention among scientists of using GMT when there is a change for ambiguity as when, say, a phenomenon is observed at the same time from different time zones? Recording local times could give the impression that the observations were hours apart, but stating the time as GMT makes it plain that they were simultaneous as GMT is the same everywhere.

Bruce