Melting at the fringes

When it comes to melting ice, the process in the oceans isn’t as straightforward as it is in a glass of water. In a new review, scientists reveal the multitude of ocean processes that contribute to ice shelf melt. The combined effect of these processes will determine future climate and sea-level rise.

Ice shelves are the result of Antarctic glaciers flowing into the ocean, where they can be melted from below (basal melting). But just how this occurs is so far, unclear.

Lead author Dr Madi Rosevear from the ARC Australian Centre for Excellence in Antarctic Science (ACEAS) and the University of Melbourne, says Antarctica is under- studied and under-sampled. She said more work needs to be done on how melting and freezing features evolve.

“One of the reasons we don’t know very much about how the oceans melt Antarctic ice shelves is because they’re hundreds of kilometres wide and hundreds of meters thick,” Dr Rosevear says.

“The ocean beneath an ice shelf is hugely difficult to access. To make matters worse, most of the important action happens within meters of the base of the ice.”

Antarctica is notoriously challenging for fieldwork, given its remote location and often harsh conditions. Many areas of the continent have never been seen by a human, which means scientists have had to find other ways to observe and understand what is happening there.

“When studying the fundamentals of how ice melts into seawater, there is a lot of important work going on in lab experiments and computer models,” says co-author Dr Bishakhdatta Gayen, also at the University of Melbourne.

“These methods complement direct observations,” she says. “In this field, it feels like each new study challenges our understanding of how melting works. It’s super exciting, and also a little daunting. That’s why we wrote this review.”

Co-author Dr Cat Vreugdenhil, also from the University of Melbourne, says “it’s clear that our old models of melting are outdated.”

“We wanted to lay the groundwork for the next generation of melting models,” Dr Vreugdenhil says. “So we could better capture Antarctica’s effect on sea level and climate.”

So, does this mean current climate models are unreliable?

“No,” says Dr Rosevear. “They’re our current best estimate. We’re always trying to refine them though, to make our projections more accurate.”

As the world warms, Antarctica’s contribution to sea level is one of the biggest sources of uncertainty. The latest IPCC report estimates that Antarctica will contribute anywhere between 3 and 34cm to sea level by 2100.

“If we lose ice shelves, the glaciers that feed them accelerate, and flow faster into the ocean, raising sea level,” Dr Rosevear says.

She says this process also makes the ocean fresher in key regions around Antarctica.

“This freshening affects the global ocean circulation,” Dr Rosevear says. “And it has important climate effects downstream.”

She says to improve climate models, the effect of fine scale melt processes needs to be integrated – and collecting more observations from the field will help.

“We’ve learned in the last decade that the under-ice landscape is very complex. There are many features in the base of the ice that remain difficult to model—but are key to understanding how quickly ice shelves melt.”

The review paper, titled “How do the oceans melt Antarctic ice shelves?” is a collaboration between ACEAS researchers at the University of Melbourne and the Australian Antarctic Division, and is available in the Annual Review of Marine Science.

REVIEW

Madelaine G. Rosevear, Bishakhdatta Gayen, Catherine A. Vreugdenhil and Benjamin K. Galton-Fenzi. (2025) ‘How Does the Ocean Melt Antarctic Ice Shelves?’ Annual Review of Marine Science.’ DOI: 10.1146/annurev-marine-040323-074354