  The origin of the observed diffuse neutrino flux is not yet known. Studies of
the relative flavour content of the neutrino flux detected at Earth can give
information on the production mechanisms at the sources and on flavour mixing,
complementary to measurements of the spectral index and normalisation. Here we
demonstrate the effects of neutrino fluxes with different spectral shapes and
different initial flavour compositions dominating at different energies, and we
study the sensitivity of future measurements with the IceCube Neutrino
Observatory. Where one kind of flux gives way to another, this shows up as a
non-trivial energy dependence in the flavour compositions. We explore this in
the context of slow-jet supernovae and magnetar-driven supernovae -- two
examples of astrophysical sources where charm production may be effective.
Using current best-fit neutrino mixing parameters and their projected 2040
uncertainties, we use event ratios of different event morphologies at IceCube
to illustrate the possibilities of distinguishing the energy dependence of
neutrino flavour ratios.
