Modelled dynamics of floating and grounded icebergs, with application to the Amundsen Sea

Abstract. Icebergs that ground on the submarine Bear Ridge in the Amundsen Sea are known to block the drift of sea ice, playing a crucial role in maintaining shelf sea ocean conditions. This important iceberg—sea ice—ocean interaction is ubiquitous around the Antarctic shelf seas. To better represent the drift, grounding, and ungrounding of icebergs in the vicinity of such seabed ridges, we introduce new dynamics into the iceberg component of the Nucleus for European Modelling of the Ocean (NEMO) ocean general circulation model. The pre-existing iceberg capability in NEMO did not facilitate iceberg grounding, but here we implement a physically-motivated grounding scheme with parameter choices guided by observations from the Amundsen Sea. When the bergs are grounded, they now experience bottom sediment resistance, bedrock friction, and an acceleration due to gravity acting down topographic slopes. We also improve the representation of ocean turbulent drag and ocean pressure gradients, both for freely-floating and grounded icebergs, by incorporating the depth-dependence of these forces. We examine the diverse set of forces acting on simulated icebergs in the Amundsen Sea, and compare our simulations with iceberg observations near Bear Ridge. The new iceberg physics pave the way for future studies to explore the existence of possible feedback mechanisms between iceberg grounding, changing sea ice and ocean conditions, and iceberg calving from the ice shelves.