An energy-conserving thermodynamic model of sea ice

We introduce an energy-conserving sea ice model for climate study that accounts for the effect of internal brine-pocket melting on surface ablation. Sea ice models that parameterize latent heat storage in brine pockets often fail to reduce the energy required for surface ablation in proportion to the internal melting that has already occurred. These models do not conserve energy during the summer melt season. Compared with our energy-conserving model, a nonconserving model underestimates top-surface ablation of multiyear ice by 12-22% and overestimates the equilibrium ice thickness by 50-124 cm. In addition, a nonconserving model is less sensitive to perturbative forcing than our energy-conserving model is: The equilibrium thickness changes 22-44% less owing to surface albedo perturbations and 13-31% less owing to downward longwave radiation perturbations. The smaller differences are associated with a model that has a time-independent, vertically varying salinity profile, and the larger differences are associated with a model that assumes the ice is isosaline with a salinity of 3.2 parts per thousand. Simulations with a vertically varying salinity profile have low salinity at the top surface compared to isosaline cases, which leads to reduced heat conduction, less internal brine-pocket melting, and more surface ablation.