A One-Dimensional Enthalpy Model for Melt and Refreezing of Saline Arctic Melt Ponds Constrained by Two-Dimensional Simulations

Melt ponds formed during summer play a crucial role in the evolution of Arctic sea ice. Observations show that the salinity in melt ponds ranges from 1 to 29 PSU, and saline ponds have different thermal properties from freshwater ponds. During the melt season, ponds with different salinities can exhibit distinct flow regimes and heat-transport efficiencies under the same radiative forcing, which can affect the relative fractions of absorbed heat that is emitted back to the atmosphere versus down into the ice. These feedbacks thus impact the evolution of pond depth. In the freezing season, the brine solution within a pond forms a porous mushy layer as it solidifies. If gravity drainage is triggered, the resulting plumes may induce complex circulation within the remnant unfrozen liquid beneath the ice lid and modify salinity transport within the underlying ice layer. These effects have not yet been fully quantified in existing models, despite their potential impact on the coupled pond–ice system.

We develop a one-dimensional pond-ice model based on an enthalpy method and a brine drainage model to explore how initial pond salinity influences the system over a melting–freezing cycle. We constrain the parameterised fluxes in the one-dimensional model using insight from a suite of two-dimensional high-resolution simulations, including double-diffusive convection and mushy-layer dynamics. Our two-dimensional simulations of double-diffusive convection during the melting stage show that salinity regulates the internal flow regime by controlling stratification, thus inhibiting turbulent convection at relatively high salinities. During the refreezing stage, two-dimensional simulations using the enthalpy method show that gravity drainage can occur across a wide salinity range, initiating turbulence even in the absence of external heat sources. This turbulence leads to highly efficient vertical salt transport. By varying the initial salinity in the one-dimensional model, we find that salinity can consequently influence both the maximum pond depth and the timescale of pond refreezing.