  We use global magnetohydrodynamic simulations, in a pseudo-Newtonian
potential, to investigate the temporal variability of accretion discs around
Schwarzschild black holes. We use the vertically-averaged magnetic stress in
the simulated disc as a proxy for the rest-frame dissipation, and compute the
observed emission by folding this through the transfer function describing the
relativistic beaming, light bending and time delays near a non-rotating black
hole. The temporal power spectrum of the predicted emission from individual
annuli in the disc is described by a broken power law, with indices of -3.5 at
high frequency and 0 to -1 at low frequency. Integrated over the disc, the
power spectrum is approximated by a single power law with an index of -2.
Increasing inclination boosts the relative power at frequencies of around 0.3
times the orbital frequency at the marginally stable orbit, but no evidence is
found for sharp quasi-periodic oscillations in the lightcurve. Assuming that
fluorescent iron line emission locally tracks the continuum flux, we compute
simulated broad iron line profiles. We find that relativistic beaming of the
non-axisymmetric emission profile, induced by turbulence, produces
high-amplitude variability in the iron line profile. We show that this
substructure within the broad iron line profile can survive averaging over a
number of orbital periods, and discuss the origin of the anomalous X-ray
spectral features, recently reported by Turner et al. (2002) for the Seyfert
galaxy NGC3516, in the context of turbulent disc models.
