  We analyse the potential vorticity of Saturn's polar regions, as it is a
fundamental dynamical tracer that enables us to improve our understanding of
the dynamics of these regions and their seasonal variability. In particular, we
present zonally averaged quasi-geostrophic potential vorticity maps between
68{\deg} planetographic latitude and the poles at altitudes between 500 mbar
and 1mbar for three different epochs: (i) June 2013 (early northern summer) for
the north polar region, (ii) December 2008 (late northern winter) for both
polar regions and (iii) October 2006 (southern summer) for the south, computed
using temperature profiles retrieved from Cassini Composite Infrared
Spectrometer (CIRS) data and wind profiles obtained from Cassini's Imaging
Science Subsystem (ISS). The results show that quasi-geostrophic potential
vorticity maps are very similar at all the studied epochs, showing positive
vorticities at the north and negative at the south, indicative of the dominance
of the Coriolis parameter 2${\Omega}sin{\phi}$ at all latitudes, except near
the pole. The meridional gradients of the quasi-geostrophic potential vorticity
show that dynamical instabilities, mainly due to the barotropic term, could
develop at the flanks of the Hexagon at 78{\deg}N, the jet at 73.9{\deg}S and
on the equatorward flank of both polar jets. There are no differences in
potential vorticity gradients between the two hemispheres that could explain
why a hexagon forms in the north and not in the south. No seasonal variability
of the potential vorticity and its meridional gradient has been found, despite
significant changes in the atmospheric temperatures over time.
