The Cosmonaut Sea off the coast of Antarctica is characterized by highly variable sea ice conditions. As the sea ice expands during the austral fall and winter, embayments, open bodies of water surrounded on three sides by sea ice, as well as polynyas often form. Using sea ice concentration data provided by satellite-based passive microwave instruments from 1979 to 2004, we characterize these embayment events by their size and temporal evolution. The data suggests a striking periodicity in the occurrence of these embayments, with the exception of a "quiet" period between 1984 and 1987. The large embayment events seem to appear approximately every three years in the same location and persist for anywhere between mid-June to mid-August. These results indicate there is predictability in the occurrence of embayment events, adding important insight into the characterization of sea ice variability in this region.