A New Energy Balance Formulation for Greenland’s Melting Bare Ice Surface

Abstract:

Greenland’s ablation zone is a complex surface during the melt-season characterized by seasonal snow cover, exposed solid bare ice, outcropping dust, surficial communities of microorganisms, and an interconnected network of melt ponds, lakes, and rivers that route meltwater into the sub/englacial system. Presently, however, surface mass balance models used to forecast Greenland’s contribution to sea-level rise treat this system simply as a solid impermeable surface with nearly constant thermal, radiative, and hydrologic properties. Here, we present a new energy balance formulation for Greenland’s melting bare ice surface which couples radiative and thermodynamic heat transfer with mass redistribution in the upper twenty meters of Greenland’s bare ice ablation zone. The model contains no tunable parameters and is constrained by in situ measurements of shortwave radiation extinction coefficient with an associated optical grain size inversion for bare ice. We test our model against multiple lines of observational evidence including direct measurements of ice sheet surface meltwater runoff, ice surface ablation, near-surface ice density, and near-surface englacial ice temperatures. We find that our model explains these observations with greater fidelity than the current generation of surface mass balance models, indicating its unique predictive ability. We conclude that reconciling modeled and observed surface mass balance in the bare ice zone is substantially improved by incorporating the radiative and thermodynamic heat transfer processes presented by this study.