Arctic Sea Ice Sensitivity to Lateral Melting Representation in a Coupled Climate Model

Abstract:

The melting of sea ice floes from the edges (lateral melting) results in open water formation and increased absorption of energy from the sun. However, lateral melt plays a small role in the sea ice mass budget in both hemispheres in most climate models. This is likely a result of simple parameterizations of this process in sea ice models that are constrained by limited observations. Here we use a coupled climate model (CESM2) to understand the sensitivity of modeled sea ice state to the lateral melt parameterization. Increasing the lateral melt rate within the range of reasonable values is largely compensated by decreases in the basal melt rate, but still results in a significant decrease in sea ice concentration and thickness (particularly at the margins). One reason may be the coarse representation of the upper ocean structure, which does not allow for the development of thin, warm layer of water in the surface of leads during summer melt season.

Results of model experiments motivated observation of the evolution of near-surface lead structure and ice edge evolution during the summer of the MOSAiC campaign in the central Arctic. The evolution of a thin (<1 m) fresh and warm layer was observed. The structure of this layer and its impact on the ice was a function of the surrounding ice characteristics, as well as the mixing and persistence of open water areas. We suggest an improved lateral melt parameterization incorporating the build-up of heat in the surface water of leads. Lateral melt is likely to become more efficient at forming open water with future sea ice loss, as both open water fraction increases and average floe size decreases.