Secondary carbonate precipitates on the surface of clasts have rarely been reported from Antarctica. Here, we infer the origin, age and palaeo-environmental significance of the calcite crusts in the Untersee Oasis, East Antarctica. The distribution of calcite crusts, which are up to 1 mm thick, is limited to locations with residual snow patches, and they have some of the highest delta O-18 (up to +17.4 parts per thousand Vienna Standard Mean Ocean Water (VSMOW)) and delta C-13 (up to +14.6 parts per thousand Vienna Pee Dee Belemnite (VPDB)) compositions of any carbonate deposits in terrestrial polar environments. Their delta O-18 and delta C-13 values are substantially enriched with respect to the isotopic values expected from equilibrium precipitation from the delta O-18 and delta C-13(DIC) (DIC = dissolved inorganic carbon) of snow meltwater. The formation of the calcite crusts is ascribed to the evaporation of residual snow meltwater and the low relative humidity and strong winds, favouring a kinetic isotope effect. The C-14 age distribution of the calcite crusts (1550 cal yr bp to modern) provides a minimum age for ice retreat and drainage of the palaeo-lake in Aurkjosen Cirque. However, in this polar desert environment in which surface melting is limited, the calcite crusts require sufficient snow accumulation and air temperatures warm enough to generate meltwater, and their age distribution corresponds to the late Holocene warm-wet climate period.