We report precise measurements of salinity, chlorinity, alkalinity, calcium, and sulphate in various types of sea ice collected at the Canadian Expedition to Study the Alpha Ridge (CESAR) Ice Camp in the Arctic Ocean and in both first-year and multiyear ice collected in Fram Strait. Several of the samples showed some relative enrichment of alkalinity and sulphate compared to what would be observed in seawater of the same salinity. The relative enrichment was quite varied and did not correspond quantitatively with what has been observed in sea ice produced in the laboratory. Our results indicate that the temperature and salinity history of sea ice must be crucial in determining the relative composition of salts in natural sea ice and that quantitative geochemical predictions based on the composition of sea ice produced in the laboratory or on a particular specimen of natural sea ice must be made with caution.