Frazil-ice formation under turbulent conditions, and its subsequent transition into grease ice and a solid pancake cover, is a key process in polar areas. Of particular importance for ocean dynamics are the salt fluxes that take place during this early stage ice transition lasting less than a few days. Observations show that grease ice initially contains about 80–90% of the salinity of the sea water from which it grows and that this rapidly decreases to 20–30% once a pancake-ice cover is established. The spatial and temporal scales of the brine convection by which this desalination takes place are, however, not well known. Here we document the transition from a grease- to pancake-ice cover using 24 hours of highly resolved infrared-based surface temperatures, water temperatures and salinity, ice-thickness and ice salinity observations. Ice was grown at the Hamburg Ship Model Basin by applying a wave field of constant frequency in a 17 m long and 3 m wide tank filled to 0.85 m with a NaCl water mixture. A fairly constant ice thickness of approximately 10 cm remained during the experiment. We discuss the temporal evolution of surface temperature signatures in terms of area fraction of grease and pancake ice and associate observed fluctuations to brine convection events.