We examined the size distribution of calcium carbonate crystals from first-year Arctic pack ice and overlying snow and slush during spring melt onset north of Svalbard. Ikaite crystals were found mainly in the bottom of the snowpack, in slush and the surface layers of the sea ice, where temperature was lower and salinity higher than in the ice below. Micrographs showed that ikaite crystals were characterized by a roughly elliptical shape with a mean aspect ratio of 1.8. The mean length of the crystals was 85.8 ± 30.2 µm (mean ±1SD) in the lateral direction and 149.3 ± 55.9 µm in the longitudinal direction. Comparisons of the salinity and the total alkalinity for melted-ice samples through the ice column suggest that the precipitation/dissolution of ikaite crystals occurred at the top of the sea ice during the ice formation/melting processes.