A new parameterization describing the health of a sea ice floe and its potential influence on wave fracture, ice deformation, and ice motion

The horizontal size of a sea ice floe directly impacts both climatic feedbacks and sea ice dynamics. The floe size distribution (FSD) quantifies how the number of sea ice floes varies with floe size across a domain. The creation of models that can reproduce an accurate representation of the FSD is paramount for both climate prediction and seasonal Arctic forecasts, as floe size contributes to the ice-albedo feedback and sea ice evolution. Within the Community Ice CodE (CICE) sea ice model, sea ice floes are modelled using a prognostic FSD, where five processes may alter the FSD: lateral growth, lateral melt, new ice creation, welding (when two different floes coagulate), and wave fracture. Field notes have observed that when two floes weld together, the two floes may be bridged with younger ice providing an intermediary. We propose that the younger ice will be weaker, making the newly welded floe more likely to fracture. Yet CICE’s prognostic FSD carries no memory of prior welding or interactions, preventing the model from capturing this history-dependent weakness and how it influences dynamical processes, such as wave fracture or floe deformation. To account for this, we introduce a new parameterization for a floe’s health that calculates the fraction of floes in a given grid cell that have recently welded and that will be most susceptible to dynamic fragmentation. The parameterization also accounts for the effects of floes healing over time (with the welded bridge thickening), the effects of dynamic fracture on floe health, and the advection of the floe health metric through the model’s domain. With our accounting of floe health, we create a linear floe health dependent feedback that strengthens the influence of wave fracture and floe deformation. Finally, we use the new floe health metric to couple the FSD to CICE’s ice strength parameterization, weakening the ice in grid cells where many floes are the product of recent welding.