Here’s one for the record books: an article about a massive hole in the Antarctic sea ice… and it doesn’t rant about climate change. In fact, it only fleetingly refers to ‘warming’, without attributing blame on humans. All this, on a media site for “those who care about our planet and environment and want to make a difference”.
I’ll pause for a moment while you pick yourselves up from the floor…
No, I’m not making this up. The article, on the website earth.com, actually manages to discuss the phenomenon of a country-sized hole in Antarctic sea ice in a rational and cool-headed scientific manner. Such instances must be saluted as the rare diamonds that they are.
Antarctica’s winter sea ice usually forms a bright lid over millions of square miles. So when a massive, black patch was spotted by NASA scientists for the first time, satellite operators were taken aback, to say the least.
Then roughly a year later, the situation got even stranger. The gap, called a polynya, swelled to the size of Switzerland and stayed open for weeks.
Only after it refroze did researchers start piecing together how such an enormous opening in the ice could appear hundreds of miles from the nearest shoreline – right above a submerged plateau named Maud Rise.
A polynya is an area of open water surrounded by sea ice. They were named with a Russian loan-word by polar explorers in the 19th century, but humans have known about them for millennia and, indeed, often depended on them for marine food sources in harsh, high latitude environments. In the Arctic, the North Water Polynya has helped human populations survive for thousands of years.
The Maud Rise polynya was first documented in the 1970s, thanks to remote-sensing satellites that began monitoring sea ice over the Weddell Sea in the Southern Ocean for the first time.
It persisted through consecutive winters from 1974 to 1976, and oceanographers at the time assumed it would become an annual occurrence. But since the 1970s, it has occurred only sporadically and for brief intervals.
So, what causes a polynya?
The Southern Ocean is normally a layer cake. A thin cap of cold, relatively fresh water floats over saltier, warmer layers, and that slight density difference keeps the column from churning.
A mid‑ocean polynya needs the cake to collapse. Salt must slip into the surface, make the top layer heavier, and flip the stack.
Once that happens, convection kicks in, the lid fractures, heat pours skyward, and the ocean “breathes” gases.
Coastal versions manage something similar each year because fierce winds shove ice away from land. Out on the high seas, though, the phenomenon is much less common.
Maud Rise, a 4,600‑foot‑tall seamount, may provide the missing ingredient by diverting currents and trapping water in tight spirals.
From 2017, scientists like Aditya Narayanan of the University of Southampton began studying the phenomenon with robotic floats, tagged elephant seals and a high‑resolution ocean model. They found that in some Antarctic winters, the Weddell Gyre, a clockwise-rotating current formed by interactions between the Antarctic Circumpolar Current (ACC) and the Antarctic Continental Shelf, sped up.
That spin drew a deep layer of warm, salty water nearer the surface, softening ice from below. Yet the meltwater should have freshened the lid and shut down mixing.
Which means multiple additional inputs.
Roaring extratropical storms supplied part of that punch. Their swirling winds flung sea ice outward and dragged briny water toward Maud Rise.
Atmospheric rivers – plumes of moist air stretching a thousand miles – added warmth from above, helping strip away stratification.
A final push came from physics first described a century ago. When wind blows across the ocean, Earth’s rotation deflects the surface flow roughly 90 degrees, a process called Ekman transport.
The model showed this flow steering salt‑laden water onto the northern flank of Maud Rise, exactly where the 2017 hole opened.
Like the rest of the Antarctic, the climatic effects of phenomena like the Maud Rise Polynya can be felt much further afield.
“The imprint of polynyas can remain in the water for multiple years after they’ve formed,” noted Professor Sarah Gille from University of California San Diego (UCSD), another co-author of the research.
“They can change how water moves around and how currents carry heat toward the continent. The dense waters that form here can spread across the global ocean.”
The more we learn about the drivers of the global climate, the less we (should) realise we understand.
