The process by which the subsurface ocean on Enceladus is heated remains a puzzle. Tidal interaction with Saturn and Dione is the leading candidate but whether the dominant heating occurs in the solid core, ice crust or in the ocean itself is an outstanding question. Here we consider the driving e ect of the longitudinal libration of the ice crust on the subsurface ocean and argue that the ow response should be turbulent even in the most benign situation of a smooth spherical ice shell when the motion of the boundary is only transmitted viscously. A rigorous upper bound on the turbulent viscous dissipation rate is then derived and used to argue that libration should be potent enough to explain the observed heat ux emanating out of Enceladus when the e ects of tidal distortion and roughness of the ice crust are included.