Distinct and synergistic influences of sea ice rheology and basal stress on the simulation of Arctic landfast ice

Arctic landfast ice (LFI) is sea ice that remains mechanically immobilized along Arctic coastlines for prolonged periods. LFI influences the stability of the Arctic halocline by displacing coastal polynyas offshore and modifying the mixing of river plumes. In large-scale ocean–sea ice models, a realistic representation of Arctic LFI relies on two interacting modelling components: a grounding (basal stress) parameterization, which establishes anchor points in shallow waters, and the sea ice rheology, which controls ice deformation between these anchors. Here we examine the sensitivity of simulated Arctic LFI to these components and to their interaction. Simulations are performed using the Nucleus for European Modelling of the Ocean–Sea Ice Modelling Integrated Initiative (NEMO-SI³) platform on a 0.25° global grid. Two contrasting rheological formulations are considered: the adaptive elastic-viscous-plastic rheology with tensile strength (aEVPts) and the brittle Bingham-Maxwell rheology (BBM), each tested with and without a grounding scheme. Owing to its elastic component, BBM exhibits a more rigid mechanical behaviour than aEVPts and more readily immobilizes sea ice between anchor points, resulting in enhanced LFI formation. However, this increased rigidity of BBM also limits ice thickening in convergence zones, thereby reducing the effectiveness of the grounding scheme through a decrease in the number of anchor points. Comparison with in situ observations of Arctic LFI thickness further highlights the importance of accurately representing the timing and duration of sea ice immobilization. When sea ice becomes immobilized early and subsequently grows predominantly through thermodynamic processes, model biases in LFI thickness are significantly reduced, consistent with Stefan’s law for thermodynamic ice growth.