Wind-Driven Waves Are Breaking Up Antarctic Sea Ice From the Inside Out, Study Finds
Buoys that drifted into East Antarctica's Vincennes Bay Polynya revealed that storm waves fracture surrounding ice, cutting ice concentration by up to 30% for at least a week.
Strong winds that keep an Antarctic ice-free patch open also build waves inside it, and during extreme events those waves can shatter the sea ice around it. That is the finding of a study in Nature Communications led by Dr. Joey Voermans, an experimental oceanographer at the University of Melbourne. The authors describe the effect as ice breaking up "from the inside out."
The paper, "Inside-outward breakup of sea ice by locally generated waves in the Vincennes Bay Polynya," looks at an area of open water off East Antarctica. A polynya is a region of open ocean surrounded by sea ice, kept clear by winds that push new ice away. Until now, most research on waves breaking ice has focused on swell arriving from the open ocean, not waves generated inside the polynya itself.
The discovery began by accident. Voermans and colleagues had placed buoys on coastal landfast ice to study Southern Ocean waves. When the ice carrying the buoys broke away and drifted into the polynya, the instruments recorded noticeably higher wave heights. That showed waves could grow large over the open water, steep enough to fracture the edges of the ice around it.
The team then turned to more than two decades of satellite data. After the most extreme wind events, sea-ice concentration around the polynya fell by up to about 30%, and the decline lasted at least a week. Concentration rose farther downwind, consistent with broken ice being carried away. The changes did not appear during similarly strong winds when conditions were less favorable for wave growth, which supports the role of waves rather than wind alone.
Breakup has a second effect. It exposes more open water to the cold atmosphere, which speeds the formation of new ice. Satellites showed more actively forming frazil ice, the slushy crystals that are the first stage of sea ice, after extreme events. In that way, the same storms that open the ice can also help produce more of it nearby.
The authors are careful about the limits. The findings come from one polynya, and the buoy crossings occurred during particularly strong wind events. How often this happens under typical conditions, and how important it is at other Antarctic polynyas, remains uncertain.
The result matters because previous research suggests Antarctic polynyas have grown over recent decades. A larger stretch of open water gives waves more room to build, which could make this breakup mechanism more common. Sea-ice models that leave out locally generated waves may be missing a process that shapes where ice sits and how much of it there is.
