Supercooled water and the bottom topography of floating ice

Observations of surface ablation and internal temperature of ice islands in the Arctic Ocean suggest the possibility of bottom accretion which cannot be explained in terms of heat conduction through the ice. It is proposed that this accretion can be caused by the advection of supercooled water forming under the surrounding normal pack ice. Since the degree of supercooling to be expected is of the order 10−2 or 10−3 °C, a direct determination of the freezing point (temperature and salinity) of the sea water in situ is experimentally difficult. To avoid this, two experiments were designed to measure supercooling indirectly by its effects, one showing the rate of accretion of an ice nucleus and the other showing the temperature difference between the sea water in its undisturbed state and, simultaneously, in the state of freezing. Both experiments conclusively showed the presence of supercooled water. The experimental results are supported by a comparison of the vertical fluxes of heat and salt in the boundary layer. The possible significance of supercooled water to the persistence of topographic features of the ice bottom is discussed.