Measurements of salinity over horizontal distances of 38 to 76 cm in thick first-year ice sheet have revealed significant differences. A maximum salinity difference of 2%0 was observed between ice core segments from the same depth. The mean standard deviation for 10-cm thickness increments through the 2.0-m ice sheet was 0.39%0 between the five closely spaced cores. The most likely mechanism for these significant differences in salinity over short distances is differential brine drainage in the ice sheet due to varying locations of brine drainage channels. A simple one-dimensional model which assumes a normally distributed arrangement of brine drainage channels provides results consistent with the horizontal differences observed.