  We consider sound wave propagation in a range-periodic acoustic waveguide in
the deep ocean. It is demonstrated that vertical oscillations of a sound-speed
perturbation, induced by ocean internal waves, influence near-axial rays in a
resonant way, producing ray chaos and forming a wide chaotic sea in the
underlying phase space. We study interplay between chaotic ray dynamics and
wave motion with signal frequencies of 50-100 Hz. The Floquet modes of the
waveguide are calculated and visualized by means of the Husimi plots. Despite
of irregular phase space distribution of periodic orbits, the Husimi plots
display the presence of ordered peaks within the chaotic sea. These peaks, not
being supported by certain periodic orbits, draw the specific "chainlike"
pattern, reminiscent of KAM resonance. The link between the peaks and KAM
resonance is confirmed by ray calculations with lower amplitude of the
sound-speed perturbation, when the periodic orbits are well-ordered. We
associate occurrence of the peaks with the recovery of ordered periodic orbits,
corresponding to KAM resonance, due to suppressing of wavefield sensitivity to
small-scale features of the sound-speed profile.
