  Ocean waves propagating through the Marginal Ice Zone (MIZ) and the pack ice
are strongly attenuated. This attenuation is critical for protecting sea ice
from energetic wave events that could otherwise lead to sea ice break-up and
dislocation over large areas. Despite the importance of waves-in-ice
attenuation, the exact physical mechanisms involved, and their relative
importance, are still uncertain. Here we present for the first time direct in
situ measurements of floe-floe interactions under the influence of waves,
including collisions between adjacent floes. The collision events we report are
aligned with the incoming wave direction, and phase-locked to the wave signal,
which indicates that the individual collisions we detect are wave-induced. The
observations demonstrate that wave attenuation by wave-induced floe-floe
collisions, which have been studied in idealized laboratory and field
experiments in the outer MIZ, are indeed a likely source of wave energy
dissipation deep inside the MIZ as well.
