  Modeling fluid turbulence using a 'skeleton' of coherent structures has
traditionally progressed by focusing on a few canonical experiments, such as
pipe flow and Taylor-Couette flow. We here consider an alternative canonical
experiment, the stratified inclined duct, a sustained shear flow whose density
stratification allows for the exploration of a wealth of new coherent and
intermittent states at significantly higher Reynolds numbers than in
unstratified flows. We automatically identify the underlying turbulent skeleton
of this experiment with a novel data-driven method combining dimensionality
reduction and unsupervised clustering of shadowgraph visualizations. We
demonstrate the existence of multiple types of energetic turbulence across
parameter space, as well as intermittent turbulence that cycles between these
types, revealing distinct transition pathways. Our method and results pave the
way for new reduced-order models of multi-physics turbulence.
