Antarctica is melting from below and scientists say it’s worse than expected

Ice shelves are massive floating extensions of glaciers that help slow the movement of enormous amounts of ice into the ocean. Scientists in Norway have now identified a process that may be speeding up their deterioration. According to the study, long channels carved into the undersides of these ice shelves can trap relatively warm ocean water, intensifying melting in specific areas.

The findings raise concerns far beyond Antarctica. As ice shelves become thinner and weaker, they lose some of their ability to hold back the glaciers behind them. That can allow more land ice to slide into the ocean, potentially accelerating global sea level rise.

Researchers say this kind of instability has already been seen in other parts of Antarctica. The Intergovernmental Panel on Climate Change (IPCC) has previously identified weakening polar ice shelves as a major uncertainty in sea level projections and a potentially serious climate risk.

Hidden Channels Beneath Antarctic Ice

The research focused on the Fimbulisen Ice Shelf in East Antarctica. Scientists discovered that the shape of the underside of the ice shelf strongly affects how seawater circulates below it.

Where deep channels exist beneath the ice, ocean currents can form small circulation patterns that keep warmer water trapped against the ice instead of allowing it to move away quickly. This concentrated warmth dramatically increases melting in those locations.

The researchers found that melting within these channels can increase by roughly an order of magnitude in some areas. In other words, the structure of the ice shelf itself helps determine where heat collects and how much damage that heat can cause.

"We found that the shape of the ice shelf underside is not just a passive feature. It can actively trap ocean heat in exactly the places where extra melting matters most," lead author Tore Hattermann from the iC3 Polar Reseach Hub in Tromsø, Norway explains.

Fimbulisen Ice Shelf sits in East Antarctica, a colder region that has generally been viewed as less vulnerable than other parts of the continent.

"We observed beneath the Fimbulisen Ice Shelf that even small amounts of warmer water can substantially increase melting within the channels," Tore Hatterman says. "As a result, the channels can grow and, in the worst case, weaken the stability of the entire ice shelf."

Qin Zhou, who co-led the study, adds that "What is striking is that even modest inflows of warmer deep water can have a large effect when the ice shelf base is channeled. That means some ice shelves that scientists usually think of as cold may be more fragile than expected."

How Scientists Studied the Ice Shelf

To investigate the process, the team combined a highly detailed map of the underside of the Fimbulisen Ice Shelf with a high resolution computer model of the ocean cavity beneath it.

The researchers tested both smoother ice shelf bases and more realistic channelled formations under cooler and slightly warmer ocean conditions. By comparing the different scenarios, they were able to isolate the effects of the channels on ocean circulation, mixing, and melting.

The study also incorporated earlier field observations collected in the region. According to the researchers, combining long term measurements with advanced modeling is essential for understanding the small scale features hidden beneath Antarctic ice shelves. Hattermann himself has spent hundreds of days living and working on Antarctic ice shelves during research expeditions.

Why Faster Antarctic Ice Melt Matters

Scientists warn that intensified melting inside the channels could create a dangerous feedback effect. As the channels deepen and widen, parts of the ice shelf may thin unevenly, reducing the shelf's overall structural stability.

If the ice shelves weaken enough, they may no longer effectively slow the glaciers flowing into the ocean behind them.

"Current climate models do not capture this effect," Tore Hattermann warns. "This means that they risk underestimating the sensitivity the 'cold' ice shelves along East Antarctica's coastline to small changes or warming in coastal waters. Such changes have already been observed, and are projected to increase in the future."

Researchers say the findings are important not only for improving climate and ice sheet models, but also for coastal planning and adaptation efforts around the world that rely on accurate sea level rise projections. The changes could also affect ocean circulation patterns and marine ecosystems surrounding Antarctica as meltwater enters the Southern Ocean.

The study, "Channelized topography amplifies melt-sensitivity of cold Antarctic ice shelves," was published in the journal Nature Communications.

The research was led by Tore Hattermann of the iC3 Polar Research Hub and Qin Zhou of Akvaplan-niva (joint first authors). Both scientists are based in Tromsø, Arctic Norway. Hattermann also serves as an assistant lead of the iC3 research group focused on developing new technologies for cryospheric science.