Modelling the Antarctic Marginal Ice Zone: Classification and Evolution in Response to Storms and Waves
Date
2025
Authors
Day, Noah Shepherd
Editors
Advisors
Bennetts, Luke
O’Farrell, Siobhan
O’Farrell, Siobhan
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Thesis
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Abstract
The Antarctic marginal ice zone (MIZ) is the dynamic outer region of the sea ice pack, where interactions with the open ocean—such as incoming surface waves and polar storms—drive complex processes and determine its width. Sea ice modulates wave energy loss through attenuation, while waves break up sea ice and constrain the size of newly formed ice floes during winter. This coupling enhances sea ice susceptibility to melting, rapid drift and deformation, influencing heat and momentum exchanges between the ocean and atmosphere and, potentially, broader climate processes. However, the pervasiveness of wave-ice processes across the ice pack remains poorly understood due to sparse observations, motivating the use of numerical models for further investigation. The first study in this thesis addresses the absence of a pragmatic method to distinguish the Antarctic MIZ from the interior sea ice pack. Traditional approaches rely on sea ice concentration thresholds due to observational constraints. This study leverages the recent implementation of wave-ice interactions in the global sea ice model, CICE6, by including a floe size distribution. Key sea ice properties indicative of MIZ processes, such as floe size, are classified statistically, and the resulting predictions of MIZ widths—defined as the distance from the ice edge to the interior pack—align with satellite-derived observations of wave activity in sea ice. This framework supports an evaluation of the MIZ width and the seasonal roles of its primary drivers in shaping its boundaries. The second study statistically evaluates the influence of storms and accompanying waves on the width of the MIZ. Findings suggest that cyclone-generated winds and transported temperatures primarily affect the ice edge, driving rapid expansion and compaction through a combination of sea ice drift and thermodynamic processes (growth and melt). In contrast, waves govern the interior boundary location, delineating the transition to the less dynamic and consolidated interior pack. These impacts exhibit strong seasonal dependence, so storms slightly expand the ice edge during winter but drive considerable retreat by early summer. Extreme changes in the MIZ width and ice edge location are attributed to wave heights and wind direction changes, respectively. The third study is motivated by recent theories suggesting a marked transition in wave-ice physics from the MIZ to a consolidated pack, driven by impedance and altered attenuation rates. A wave-ice interaction model is used to evaluate the impact of considering this transition on further ice breakup and wave attenuation. Sensitivity tests indicate that treating MIZ ice as having distinct physical properties from interior ice increases the sensitivity of breakup to wave parameters. If wave directionality is unknown, statistical methods can misidentify attenuation regimes. The collective findings demonstrate that the winter Antarctic sea ice pack creates unique conditions that sustain large ocean waves despite high ice concentrations. The MIZ undergoes significant seasonal transformations in sea ice properties and dominant processes from winter to summer. This thesis establishes the requirements for identifying the Antarctic MIZ and provides new insights into its variability and drivers from mesoscale to circumpolar scales.
School/Discipline
School of Computer and Mathematical Sciences
Dissertation Note
Thesis (Ph.D.) -- University of Adelaide, School of Computer and Mathematical Sciences, 2025
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This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at: http://www.adelaide.edu.au/legals