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| Natura: | Recurso digital |
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Zenodo
2026
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| Accesso online: | https://doi.org/10.5281/zenodo.19236596 |
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Sommario:
- <p><span lang="EN-GB">Icebergs play a key role in the climate system by distributing about half of the glacial freshwater released by Antarctica to the Southern Ocean. Some icebergs get grounded on shallow ridges and play the role of an anchor for sea ice, with thicker sea ice often fastened to them. Such fast ice favours the opening of coastal polynyas, where most Antarctic sea ice is produced. The climatic importance of icebergs has motivated the development of models that treat icebergs as Lagrangian particles driven by forces exerted by the atmosphere, ocean, and sea ice. In current models, however, these Lagrangian icebergs do not interact with bathymetry, i.e., they do not ground on shallow bathymetric ridges as observed. This limits our ability to project future sea-ice production rates and water mass transformation, including Antarctic Bottom Water formation.</span></p> <p><span lang="EN-GB">Here, we present the development of a new-generation Lagrangian iceberg model capable of interacting with bathymetry. First, this has required additional work to improve estimates of iceberg thickness. Most previous studies used a thickness of 250 m for the largest iceberg classes, following the typical ice-shelf thickness suggested by a limited number of ship observations, and independently of the calving location. In the new model version, icebergs inherit the thickness of their calving ice shelf, and their keel depth often exceeds 400 m, making them more likely to ground on bathymetric ridges. The second part of our work has involved explicitly representing the dissipative forces at the base of the iceberg as it moves over shallow bathymetry. This includes the representation of both the energy dissipation when icebergs penetrate into a sediment layer of a few meters thick, and the Coulomb friction against the solid bedrock if the iceberg penetrates all the way through the sediment layer. In the case of a contact with the solid bedrock, the iceberg's kinetic energy is converted into potential energy, and the iceberg is lifted above floatation.</span></p> <p><span lang="EN-GB">From these developments, we show that the first effect of iceberg grounding is to keep the meltwater closer to Antarctica, and the second effect is to favour the formation of fast ice and polynya. Both significantly affect the vertical structure of the ocean around Antarctica. We were also able to propose a quantitative force balance for both freely floating and grounding icebergs. A three-force balance between wind stress, the ocean pressure gradient and the Coriolis force largely explains the motions of freely floating icebergs, with little net acceleration, as all these forces are nearly perpendicular to motion. The interaction with sediments alters this: icebergs are mostly pushed forward by wind, with strong deceleration due to sediment resistance. In cases where icebergs interact with the solid bedrock, they usually stop within a day.</span></p>