Observations of time-dependent changes in microwave emission from thin (0--9 cm) saline ice were made at frequencies of 6.7, 10, 19, 37, and 90 GHz for both vertical and horizontal polarizations. Experiments were carried out on artificial sea ice in the laboratory and on natural ice in the Greenland Sea. Coincident data were also collected on ice thickness, temperature, and salinity together with a variety of basic meteorological data. Several phenomena were found to be common to all the laboratory measurements, with some indication that similar features were also present in the field data. These include (1) a sharp rise in surface temperature when the ice was between 1 and 2 cm thick, apparently unreleated to any environmental changes, (2) a decrease in brightness temperature (Tb) at 37 GHz during or just after after the surface temperature rise, and (3) and initial increase in Tb with increasing ice thickness, followed by substantial decreases in Tb at the higher (19, 37, and 90 GHz) frequencies. The maximum Tb values observed were higher than those previously reported for young ice. Tb was also found to be much more sensitive to variations in ice properties at horizontal polarization than at vertical polarization. Numerical modeling results indicate that the high-frequency decreases in Tb were not due to bulk changes in either ice temperature or salinity. The most likely explanation for the observed rise in surface temperature and decrease in Tb was the formation of a salinity-enhanced ice or brine surface layer caused by the upward transport of brine as the ice grows. ¿ American Geophysical Union 1993