The vibration modes of a clean Cr2O3(0001) surface have been studied under ultra high vacuum conditions with high-resolution electron energy loss spectroscopy. A mode which is confined to the first few atomic layers of the oxide was detected in addition to the Fuchs-Kliewer phonons. In contrast to the Fuchs-Kliewer phonons which extend deeply into the hulk, this mode is very sensitive towards the presence of adsorbates. Full-potential linearized augmented plane-wave calculations show that this mode is an in-phase oscillation of the second-layer oxygen atoms and the Cr atoms of the two layers below.