the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Collision with Seamount Triggers Breakup of Antarctic Iceberg
Abstract. Iceberg A68a calved from Larsen C ice shelf, experienced several major calving when drifting around the South Georgia Island in late 2020. Here, we show for the first time that the decisive factor for its calving was a collision with the surrounding seamount. By treating the iceberg as a deformable body in an established ice-flow model, we show how its collision with the seafloor created huge stresses within the iceberg that led to its disintegration. The drifting and rotating of the iceberg, while grounded, further enhanced its breakup. Moving over a grounded shoal increased the tensile stresses by a factor of almost one hundred more than immobile grounding alone, and rotational motion about the pinning point increased the stresses by another twenty percent. Modeling the fracture and breakup of a large tabular iceberg is an essential step toward better understanding the life cycle of an iceberg. The possible collapse of the marine-based sectors of the great ice sheets in a warming world may lead to a massive increase in the number of icebergs in the surrounding oceans. It will be crucial to be able to understand where such icebergs drift and how they ultimately disintegrate into the ocean.
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Status: open (until 08 Jan 2025)
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RC1: 'Comment on egusphere-2024-2790', Anonymous Referee #1, 22 Nov 2024
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In this study, Wang and co-authors investigate how a piece broke off iceberg A68 when it collided with the seafloor near South Georgia in 2020. While our understanding of iceberg-ground collisions are limited and there is a need to find ways to represent these processes in models, I don't see a clear path for this manuscript to contribute a significant advancement. Two central concerns are
(1) The documentation of the collision and resulting breakup is not new. Huth et al (2022) presented on this rather clearly, including a representation of the breakup in their modeling account, which uses a bonded-particle iceberg [I am not a co-author of that paper]. Therefore, the contribution here would be to gain fundamental insight into the physical processes of how iceberg-ground collisions drive breakup, and I don't believe this is convincingly provided. This brings me to my 2nd comment.
(2) The authors use Ua to model this collision and breakup. This is a rather befuddling choice of model, since Ua is an idealized large-scale ice flow model using a shallow shelf approximation. My understanding is that it is designed to model viscous creep of ice sheets/shelves over long time periods and at large spatial scales, not the rapid and comparatively small-scale fracture of icebergs. The choice of this model is not justified in the text, nor are potential issues with temporal or spatial resolution discussed in any way.
One way forward I can see for this study to become a valuable contribution is through validating that the Ua model can indeed meaningfully represent such fracture events. This could be done for example by comparing it to a model that represents the iceberg as an elastic/brittle object (which is the relevant rheology on the fast time scales of fracture events). This would entail a considerable amount of extra work and lead to a fundamental reframing of the study.Â
Citation: https://doi.org/10.5194/egusphere-2024-2790-RC1
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