Scientists call this the marginal ice zones (MIZ). It is located at the very southernmost tip of the globe where ocean meets massive ice walls.
The region of the sea ice is heavily influenced by ocean processes and waves, especially in open waters.
For many years, scientists have been trying to locate the “outer edges” of sea-ice. They used to use satellite-derived concentration maps of sea-ice, which were divided into thresholds.
These maps are informative but they do not have the MIZ’s key characteristic: the waves. The MIZ, without waves, is a mere cartographic membrane.
With them, however, it becomes a physical and climatic interface.
Early laser altimetry studies confirmed the waves’ penetration of ice. However, cloud coverage limited such measurements.
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Scientists have developed a technique that allows them to determine, for the very first time, an important and understudied region in the Antarctic sea-ice. The technique relies on advanced radar altimetry data, namely Ka-band altimeter (obtained between 2013-2024), that can penetrate the atmospheric veil and obtain observations in this crucial yet understudied area of the Antarctic Sea-Ice System.
The first 10 year climatological definition of the MIZ affected by waves was produced.
This description is constrained to the physical processes that are responsible.
About 16% of Antarctica’s sea-ice is influenced by waves. It is an area of ocean that constantly interacts with waves and ice.
It does not cover the entire space.
MIZs change with seasons and are affected by local conditions. The position of the edge of the ice in relation to the true north also has a great impact on its size. The angle of the waves hitting the ice is a major factor in the MIZ’s width.
The Antarctic MIZ is described by this climatology as an interesting mix, not just a ridge along the ice edge. Waves can reach deep into the ice in certain places, creating an even wider MIZ. Other times, the ice prevents waves from reaching the boundary, creating a smaller one. Wave-affected MIZ surface widths average 35-180 km.
The widths of these patterns change according to the season and the longitude.
This pattern is also affected by seasonal cycles. The MIZ shrinks during winter due to the thick sea ice. When the sea ice recedes in summer, the MIZ becomes more exposed to waves.
The nuanced image challenges outdated assumptions. The MIZ, as shown here, is not passive, but an active system that’s driven by seasonal changes, geography and the directionality of waves.
Alex Fraser from the Australian Antarctic Program Partnership is the lead author of this article. The MIZ is traditionally defined by the satellites as the area with a concentration of sea ice between 15% and 80%. The World Meteorological Organization’s (WMO) definition of the MIZ is not based on sea-ice density. It refers to the region where waves penetrate the ice and cause it to melt.
The wave action in the MIZ makes it a dynamic area of intense ocean-ice and atmosphere interaction.
But before our study we did not know exactly how the Antarctic MIZ varied seasonally, both spatially and temporally.
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What is the significance of this? The MIZ plays a vital role in Earth’s climate, regulating sea ice breaking up, controlling heat and carbon transfer between ocean and atmosphere and supporting ecosystems along the edge of the ice.
The MIZ’s impact and width could be used to model the response of Antarctic sea ice to climate change.
“Dr. Fraser” said Dr. Fraser When waves don’t affect the sea ice, the ice forms a complete “cap” on the ocean. This limits the exchange of gases, such as carbon dioxide, with the air. The exchanges increase when waves break up the ice.
The MIZ also protects inner-pack, fast, and shelves of ice from the waves and supports marine life by allowing strong phytoplankton to bloom at retreating edges, which feeds krill, and in turn penguins and seals.
By improving the radar altimetry, it is possible to extend MIZ records by decades, or even decades, earlier than previously recorded data, and up until a few years before satellite coverage. The retrospective record provides an opportunity to determine whether the Southern Ocean is experiencing stronger storms that are pushing back ice edges more than in previous times.
This could have implications on future Antarctic climate.
Noah Day, co-author of the study from the School of Mathematics and Statistics of the University of Melbourne, tested satellite data against a model of wave-ice.
The model explained 85% of variance with its predictions.
The modeling revealed that simple wave-ice dynamics can capture accurately the seasonal variation of MIZ thickness, which suggests that large-scale MIZ variations are primarily controlled by incoming waves.
The seasonal cycle identified by this study is different from the traditional concentration-based definitions that often predict MIZ to be at its widest during summer. “The strong agreement between wave-ice model and observations is encouraging for future research investigating the MIZ’s role in the Southern Ocean climate system.” “Dr. Day”
It may appear to be a tiny section of ocean but the marginal ice zone is of vital importance for our planet. Here, the energy of the ocean interacts delicately with the cryosphere. Here, the effects of climate change are first seen.
The new Antarctic climatology is more than just data; it gives us a peek into Antarctica’s living edge.
The MIZ is a complex, dynamic region that regulates waves and occupies one-sixth the area of sea-ice. This shows us how the ocean moves at the edge of our planet.
The study is a key resource for Dr. Klaus Meiners of the Australian Antarctic Division. He uses it to plan a trip in 2028 aboard Australia’s RSV Nuyina national icebreaker.
Now that we know the seasonal MIZ’s width in Antarctica and have observed them for a decade, we can steer our ship accordingly. He said. “During our voyage, we will use real-time data analysis using new methods that were developed for this study. This information will guide us and help adapt to the changing conditions of the ocean.”
Understanding the main drivers for the Antarctic MIZ’s width and the impact of varying swell direction on MIZ’s width helps us develop the most effective survey design to conduct our fieldwork in East Antarctica.
Journal Reference
- Alexander D.
Fraser, et. al., “Revealing Antarctic marginal ice zones with a decade long wave-in ice climatology”, Nature Communications, 2026. DOI: 10.1038/s41467-026-73203-z
