  The possibility of subcritical behaviour in the geostrophic turbulence regime
of rapidly rotating thermally driven convection is explored. In this regime a
non-local inverse energy transfer may compete with the more traditional and
local direct cascade. We show that, even for control parameters for which no
inverse cascade has previously been observed, a subcritical transition towards
a large-scale vortex state can occur when the system is initialized with a
vortex dipole of finite amplitude. This new example of bistability in a
turbulent flow, which may not be specific to rotating convection, opens up new
avenues for studying energy transfer in strongly anisotropic three-dimensional
flows.
