  We study supernova-driven galactic outflows as a mechanism for injecting
turbulence in the intergalactic medium (IGM) far from galaxies. To this aim we
follow the evolution of a 10^13 Msun galaxy along its merger tree, with
carefully calibrated prescriptions for star formation and wind efficiencies. At
z~3 the majority of the bubbles around galaxies are old (ages >1Gyr), i.e. they
contain metals expelled by their progenitors at earlier times; their filling
factor increases with time reaching about 10% at z<2. The energy deposited by
these expanding shocks in the IGM is predominantly in kinetic form (mean energy
density of 1 \mu eV cm^-3, about 2-3 x the thermal one), which is rapidly
converted in disordered motions by instabilities, finally resulting in a fully
developed turbulent spectrum whose evolution is followed through a spectral
transfer function approach. The derived mean IGM turbulent Doppler parameter,
b_t, peaks at z~1 at about 1.5 km/s with maximum b_t = 25 km/s. The shape of
the b_t distribution does not significantly evolve with redshift but undergoes
a continuous shift towards lower b_t values with time, as a result of bubble
aging. We find also a clear trend of decreasing b_t with N_HI and a more
complex dependence on R_s resulting from the age spread of the bubbles. We have
attempted a preliminary comparison with the data, hampered by the scarcity of
the latter and by the challenge provided by the subtraction of peculiar and
thermal motions. Finally we comment on the implications of turbulence for
various cosmological studies.
