The distribution of impurities in an ice sphere was examined by melting an ice sphere formed from a solution containing phosphate and ammonium ions as impurities. To interpret this biased distribution, the adsorption phenomena of phosphate and ammonium ions on the surface of ice crystals were also experimentally examined. The adsorption experiments were performed by forming ice into spherical shapes and immersing the spheres in a solution containing phosphate and ammonium ions under a limited range of solution temperatures from 0 to 0.4degreesC. The results showed that the phosphate and ammonium ions were adsorbed on the ice surface immediately after the immersion. The amounts adsorbed after the establishment of a quasi-equilibrium state obeyed a Langmuir adsorption isotherm. Based on the adsorption isotherm, we proposed a quantitative explanation for the distributed ions in the ice sphere.