Underwater ambient noise spectra are described for data recorded during late spring conditions under the ice sheet in McMurdo Sound. The ambient noise was at all times marked by intense biological activity, but a diurnal component became apparent during a three‐day recording period. This noise was found to be similar to that described in Arctic work and undoubtedly arose as the result of surface cracking under the influence of thermal stressing. The characteristics of this noise component, however, were found to differ in certain respects from those reported from comparable Arctic measurements.Subject Classification: [43]30.20, [43]30.70; [43]28.65.