  In nature turbulent flows exist that are neither simply 2D nor 3D but
boundary conditions, such as varying stratification, force them towards the one
or the other. Here, we report the first evidence of the co-existence of 2D and
3D turbulence in an experimental flow driven by Faraday waves in water. We find
that an inverse energy cascade at the fluid surface and a direct energy cascade
in the 3D bulk flow underneath exist simultaneously. We base our analysis on
temporally and spatially well-resolved velocity fields measured at horizontal
and vertical planes. The findings suggest that the strongly turbulent 2D
surface flow drives the 3D bulk flow through sporadic vertical jets as a source
of momentum.
