We describe energy fluxes involved in melting ice in the proglacial lake Jökulsarlon and the transport of thermal energy into the lake from the atmosphere and the sea. Data from earlier fieldwork and campaigns have been used to estimate the net radiation balance, the turbulent fluxes, the heat provided by inflowing seawater, and the glacial meltwater flux. From aerial photographs, DGPS measurements, and mass balance measurements, we calculated a calving flux of 260 × 106 m3 yr−1 for the present. The total energy required to melt all the ice in the lake is approximately 160 W m−2 assuming that all the calved ice is melted during 1 yr. The most important contribution is heat from seawater. Radiation provides approximately 70 W m−2. The albedo depends on the ice-covered fraction of the lake and ranges from 22% in summer to 41% in winter. The turbulent fluxes are around 10 W m−2. Difficulties occurred in finding an appropriate range for the roughness parameter z0, but the most likely values are in the range of a few centimeters. We considered different future scenarios with respect to inflow of seawater and air temperature, albedo, and even inhibition of seawater intrusion, which would have a significant impact on ice cover in the lake.
