  When a dense monolayer of macroscopic slightly polydisperse spheres floats on
chaotic capillary Faraday waves, a coexistence of large scale convective motion
and caging dynamics typical for jammed systems is observed. We subtract the
convective mean flow using a coarse graining and reveal subdiffusion for the
caging time scales followed by a diffusive regime at later times. To test the
system in the light of dynamic criticality, we apply the methods of dynamic
heterogeneity to obtain the power-law divergent time and length scales as the
floater concentration approaches the jamming point. We find that these are
independent of the application of the coarse graining procedure. The critical
exponents are consistent with those found in dense suspensions of colloids
indicating universal stochastic dynamics.
