GODAR: a new discrete element sea ice model

Sea ice is a highly heterogeneous, granular material whose mechanical behavior arises from interactions among individual floes. This granular nature makes discrete element methods (DEMs) a natural choice for modeling sea ice dynamics. In principle, DEMs can resolve discontinuities, such as fractures and leads, and directly capture deformation, ridging, and dilatation processes without relying on parameterizations. However, several challenges (e.g., contact detection, floe geometry, open water treatment) limit their applicability to large-scale simulations. For these reasons, computational efficiency, and historical precedent, continuum models have long been the community’s choice for simulating sea ice at larger scales, even though they face their own challenges. Although running high-resolution (<2 km) state-of-the-art continuum models improves the representation of linear kinematic features (LKFs) and deformation statistics, this is computationally expensive, and Earth system models running at coarser resolutions can’t benefit from this. Thus, they are supplemented with parameterizations to account for subgrid-scale processes that cannot be captured by rheological models alone. Therefore, a modeling framework that bridges the gap between particle-resolving and continuum scales is required.

We present a new sea ice discrete element model, the Granular flOe Dynamics for seA ice Rheology (GODAR) model, to bridge the gap between the engineering and pan-Arctic scales. The purpose of this model is to support the development of parameterizations representing the granular behavior of sea ice in continuum sea ice models. GODAR includes a ridging parameterization, a rolling-resistance model that captures complex geometries, and a novel sheltering parameterization. The model explicitly resolves the formation and evolution of LKFs and reproduces the dilatant behavior observed in granular materials, while maintaining computational tractability suitable for regional domains by using cylindrical particles. Results from shear experiments demonstrate that ridges are highly localized along the failure planes and that the ridge build-up coincides with a positive angle of dilatancy (compressive regime). The novel geometric sheltering coefficient can reduce the total form drag of the sheltered floes, resulting in a non-zero moment on assemblies of floes. Finally, GODAR could be easily improved to run basin-scale simulations in the near future, and be extended to a seamless model capable of representing all ice types – sea ice, icebergs, ice shelves, and land ice – within a unified framework.