The landfast sea ice in McMurdo Sound, Antarctica, grows through two processes: conduction of latent heat from the ice/ocean interface to the atmosphere and growth of ice directly into supercooled wate sourced from the nearby Ross and McMurdo Ice Shelves. The presence of supercooled water and its cloud of suspended frazil modifies the crystal structure of the sea ice and contributes to the ice thickness. To measure these processes it is necessary to be present while the ice is growing. Working out of Scott Base, we occupied a site in McMurdo Sound over the winter of 2009. Two thermistor probes with a 30 mm sensor spacing were frozen in and recorded the thermal evolution of the sea ice as it grew from 0.88 m (late May) to 2.08 m (late October). A sequence of cores was taken over the winter from a nearby location to determine the evolution of the salinity and crystal structure of the sea-ice cover. By late October the ice consisted of 0.12 m frazil ice, 0.88 m columnar ice, 0.40 m mixed columnar/platelet ice and 0.68 m platelet ice. Mean sea-ice salinity for each of these sections was 9.8, 6.6, 5.1 and 5.3, respectively. Ocean currents, temperature and salinity were recorded using moored instruments and repeated full-depth CTD casts close to the ice study site over the winter. We interpret our series of sea-ice salinity measurements in relation to the conductive, latent and oceanic heat fluxes at the ice/water interface determined from in situ temperature measurements. We link the growth history of the sea ice to events in the ocean and find the contribution of supercooled water, sourced from ice shelves, to the growth of coastal Antarctic sea ice.