  We use a general relativistic approach to investigate the effects of weak
cosmological magnetic fields on linear rotational perturbations during the
radiation and dust epochs of the universe. This includes ordinary kinematic
vorticity, as well as vortex-like inhomogeneities in the density distribution
of the cosmic medium. Our study confirms that magnetic fields can source both
types of perturbations and shows that their presence also helps cosmic rotation
to survive longer. In agreement with previous Newtonian studies, we find that
during the dust era vorticity decays slower than in non-magnetised cosmologies.
Prior to equipartition the magnetic effect is more pronounced, since it helps
the aforementioned rotational distortions to maintain constant magnitude.
Overall, magnetised universes seem to provide a much better environment for the
survival of cosmic vorticity than their magnetic-free counterparts.
