The role of the oceanic heat flux Fw in the sea ice energy and mass balance is discussed, and a method is described for determining Fw from measurements of the temperature and thickness of sea ice. Results obtained using this method and data collected in the fall of 1988 during a drift in the eastern Arctic northeast of Fram Strait are presented. Estimates of Fw ranged from 0 to 37 W m−2 and varied in both time and space. The gradual variation over the course of the drift reflects transformation of the West Spitsbergen Current into Arctic water masses. A significant intersite variability on horizontal scales of 10 to 100 m is ascribed to the interaction between under-ice topographic features and turbulent energy and mass transfer in the boundary layer. In addition, there is a variability in the ice growth rate on horizontal scales of 0.1 to 1 m which is ascribed to the instability of the ice-ocean phase boundary in the presence of turbulent flow. These observations have implications for modeling and future experiments.