Swirling underwater storms are aggressively melting the ice shelves of two vital Antarctic glaciers, with potentially far-reaching implications for global sea level rise, a recent study has revealed.
Antarctica is like a fist with a skinny thumb stuck out towards South America. Pine Island Glacier is near the base of this thumb. Thwaites — known as the Doomsday Glacier because of the devastating impact its demise would have on global sea level rise — sits next to it.
Over the past few decades, these icy giants have experienced rapid melting driven by warming ocean water, especially at the point where they rise from the seabed and come afloat as ice shelves.
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The new study, published last month in Nature Geosciences, is the first to systematically analyse how the ocean is melting ice shelves over just hours and days, rather than seasons or years, its authors say.
"We are looking at the ocean on very short 'weather-like' timescales, which is unusual for Antarctic studies," said Yoshihiro Nakayama, a study author and an assistant professor of engineering at Dartmouth College.
The underwater storms they focused on — called submesoscales — are fast-changing, swirling ocean eddies.
"Think of these like little water twirls that spin around really fast, kind of like when you stir water in a cup," said study author Mattia Poinelli, an Earth system science researcher at the University of California, Irvine and a NASA research affiliate. However, in the ocean, these eddies are not small — they can span up to 9.5 kilometres.
They form when warm and cold water meet. To return to the cup analogy, it's the same principle as when you pour milk into a cup of coffee and see tiny swirls spinning around, mixing everything together.
The phenomenon is similar to how storms form in the atmosphere — when warm and cold air collide — and like atmospheric storms, they can be very dangerous.
The eddies spin up in the open ocean and race underneath ice shelves. Sandwiched between the complex, rough base of the ice shelf and the seafloor, the eddies churn up warmer water from deeper in the ocean, which enhances melting when it "hits" vulnerable ice, Nakayama said.
The scientists used computer models as well as real-world data from ocean instruments to analyse the impact of these underwater storms.
They found that, together with other short-lived processes, the storms caused 20 per cent of the melting at the two glaciers over a nine-month period.
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"Quantifying the precise contribution of storms alone is challenging because of their chaotic nature," Poinelli said. But these events look to have a big role over short time frames.
The researchers also highlighted a worrying feedback loop. As the storms melt the ice, they increase the amount of cold, fresh water entering the ocean. This mixes with warmer, saltier water beneath, generating more ocean turbulence, which in turn increases ice melting.
"This positive feedback loop could gain intensity in a warming climate," said study author Lia Siegelman of UC San Diego's Scripps Institution of Oceanography.
The consequences could be grave as the ice shelves play a vital role holding back the glaciers, slowing their flow into the ocean. Thwaites Glacier alone holds enough water to raise sea levels by more than 2 feet. But, because it also acts as a cork holding back the vast Antarctic ice sheet, its collapse could ultimately lead to around 10 feet of sea level rise.
The study is important "because it sheds light on the role of small features in the ocean melting the base of ice shelves," said Tiago Dotto, a senior research scientist at the National Oceanography Centre in the UK.
The extent of the ice melt the study found was "astonishing," he told CNN.
There are still huge uncertainties. Antarctic ice shelves are among the least accessible places on Earth, meaning scientists have to rely heavily on simulations. "These kinds of studies are intriguing but they are computer models," said David Holland, a professor of mathematics and atmosphere and ocean science at NYU.
Much more real-world data is needed to really understand the impact of these eddies, along with other ocean weather, he told CNN.
There are also many drivers of ice melt in this vast continent. "Hundreds of things are of similar importance to the decay of the ice sheet," said Ted Scambos, senior research scientist for the Earth Science and Observation Center at the University of Colorado Boulder.
"Awareness of the dynamics of the near-ice-sheet ocean is evolving rapidly," he told CNN.
The study is clear that more data is needed to understand how underwater storms may vary over seasons and years. Nevertheless, these short-term weather-like processes are "far from negligible," Poinelli said.
"Studying these fine-scale ocean phenomena is the next frontier when it comes to the ocean-ice interactions that help us understand ice loss and, ultimately, sea level rise," Siegelman said.
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