Hey, fun question!
Actually, time zone boundaries are determined by the vagaries of
politics. Some time zones (especially those enclosing little islands in
the Pacific) even are not at hour intervals from each other, and have
shapes that include just the island. Most of the Earth is divided into
time zones that look like the striped surface of a pumpkin, but there
are wiggles and detours and all sorts of craziness to some time zone
boundaries. But that doesn't address your question, other than to say
that time zones are things that we people get to define for our own
convenience. Time zones are constructed so that the sun rises in the
morning hours and sets in the evening hours, and they give people who
travel from faraway places or who communicate with other people in
faraway places a convenient way to adjust watches.
Let's consider what happens at the poles. At the pole, the length
of one day is one year. The sun stays up all summer, sets in the fall,
and rises again the following spring. So there is no need to
synchronize a clock with the rising and setting of the sun. The other
thing we want is for people who travel to the poles, or who communicate
with those at the poles, to know something about the schedules of those
who are there (so as not to try to communicate with them when they are
sleeping, for insance). Then people should just agree in advance what
the time to set the clock to and stick to it.
I'll bet that for international scientific stations, like the one
very close to the South Pole in Antactica, "Universal Time" (the time
at the observatory in Greenwich, England) is used. At least it's
unambiguous. But one could also set one's clock to match that of the
science team's collaborators who may come down to visit from time to
time or radio in.
(published on 10/22/2007)