Scientists measure 16% of Southern Ocean sea ice waves affect
Scientists have measured the southern ocean's wave-affected Antarctic sea-ice edge for the first time, using satellite radar to map how waves reach into the Marginal Ice Zone. The study found that around 16% of the Antarctic sea-ice zone is wave-affected, giving a direct estimate of a region that had long been described with proxy thresholds rather than wave penetration.
Dr. Alex Fraser, lead author from the Australian Antarctic Program Partnership at the University of Tasmania, said the work answers basic questions about where the MIZ really is. "Traditionally, the MIZ has been defined as the region with sea-ice concentration between the arbitrary thresholds of 15% and 80%, as seen by satellites. However, sea-ice concentration has nothing to do with the actual MIZ definition from the World Meteorological Organization (WMO): 'the region of ice cover which is affected by waves and swell penetrating into the ice from the open ocean.'"
Satellite radar over 12 years
The researchers used a 1980s technique on a radar altimeter aboard an orbiting French-Indian satellite launched in 2013, then measured wave heights entering the sea ice over a 12-year period from 2013 to 2024. Radar altimeters can see through cloud cover, which let the team trace the wave-affected zone across seasons rather than rely on surface ice concentration alone.
The result is a wave-affected Marginal Ice Zone that averages about 35 to 180 kilometers wide and forms a nearly 200-kilometer-wide ring of ice floes influenced by Southern Ocean waves. Winter and early spring are the times when that zone is widest.
University of Tasmania study
The research was led by the University of Tasmania in collaboration with the University of Melbourne and other institutions, and it was published in Nature Communications. Fraser said the study shows why the area is more than a boundary line on a map. "The wave action makes the MIZ a highly dynamic region of intensive ocean-ice-atmosphere interaction, but before our study, we didn't really know how the Antarctic MIZ varies seasonally in space and time."
Fraser also said the zone affects what happens when sea ice either blocks or opens exchange with the atmosphere. "That's important because when sea ice isn't affected by waves, it forms a more complete 'cap' on the ocean, limiting the exchange of heat, moisture and gases (e.g., carbon dioxide) with the atmosphere. When waves jostle the ice and break it up, gaps between ice floes allow these exchanges to increase."
Antarctic ice shelves and marine life
Fraser added that the Marginal Ice Zone helps shield inner-pack ice, fast ice, and ice shelves from waves, and supports marine life when meltwater at the retreating ice edge drives phytoplankton blooms that feed krill, penguins, seals and whales. The study places a number on how much of Antarctica's sea-ice zone is exposed to that process: 16% of the Antarctic sea-ice zone is wave-affected, a figure drawn from the 2013 to 2024 measurements.
For readers following Antarctic sea ice, the practical shift is that the outer edge can no longer be treated as a broad satellite threshold alone. The new measurement gives researchers a way to compare seasons, track change in the southern ocean, and judge where the wave-driven transition into the ice is widest as winter and early spring set the outer boundary most dramatically.
