Rapid Antarctic glacier retreat sparks scientific ‘whodunnit’

A new study suggests that the recent rapid retreat of the Antarctic glacier may be unprecedented, a finding that could have major implications for future sea level rise.

The researchers found that Hectoria Glacier retreated by more than 8 kilometers (5 miles) in just two months in late 2022.

The authors believe it could be the first modern example of a process in which the front of a seafloor glacier is rapidly destabilized.

But other scientists argue that this part of the glacier was already floating in the ocean, so although the changes are impressive, they are not unusual.

The floating tongues of glaciers extending out to sea — called ice shelves — are more vulnerable to breaking up than the fronts of glaciers resting on the sea floor.

This is because they can be eaten more easily by the warm water underneath.

The fact that Hectoria has undergone tremendous changes is indisputable. Satellite data show that its front retreated by about 25 kilometers (16 miles) between January 2022 and March 2023.

But unraveling the causes is like a mystery to the “crime,” according to the study’s lead author Naomi Oshawat, a research affiliate at the University of Colorado Boulder and a postdoctoral researcher at the University of Innsbruck.

The case began in 2002 with the extraordinary collapse of an ice shelf called Larsen B on the East Antarctic Peninsula. About 3,250 square kilometers (1,250 sq mi) of the ice shelf were lost, roughly the size of Cambridgeshire or Gloucestershire.

Larsen B was effectively holding back the Hectoria Glacier. Without this, Hectoria’s movement would accelerate and the glacier would weaken.

But the bay vacated by the ice shelf eventually filled with sea ice “anchored” to the sea floor, helping to partially stabilize Hectoria.

That was until early 2022, when the sea ice broke up.

What followed was the loss of more floating ice from Hectoria’s front, as large, flat-topped icebergs broke off or “snapped off,” and the ice behind them accelerated and thinned.

This is not unusual. The calving of icebergs is a natural part of the behavior of ice sheets, even though it is man-made Climate change It makes the loss of ice shelves more likely.

What was unprecedented, the authors argue, was what happened in late 2022, when they suggested that the front of the glacier was “anchored” – resting on the sea floor – rather than floating.

In just two months, Hectoria retreated by 8.2 km. That would be nearly 10 times faster than any glacier ever recorded before, according to the study published in 2019. Natural Earth Sciences.

The authors say this extraordinary change could be thanks to the ice plain, a relatively flat area of ​​rock on which the glacier rests lightly.

They say rising forces from ocean water can “lift” thin ice all at once, causing the icebergs to break off and the glacier to retreat in quick time.

“Glaciers don’t usually retreat that quickly,” said co-author Adrian Lockman, professor of geography at Swansea University.

He added: “The conditions may be a little special, but this rapid retreat shows us what may be happening elsewhere in Antarctica, where glaciers stabilize slightly and sea ice loses its grip.”

What makes this idea even more exciting, the authors say, is that this process has never been observed in the modern world. but Marks on the sea floor It suggests that they may have caused rapid ice loss to the ocean in Earth’s past.

“What we’re seeing in Hectoria is a small glacier, but if something like this happens in other areas of Antarctica, it could play a much bigger role in the rate of sea level rise,” Dr Oshawat said.

This could include Thwaites – the The so-called “Doomsday” glacier. Because it contains enough ice to raise global sea levels by 65 cm (26 in) if it melted completely.

“It’s really important to understand whether or not there are other areas of ice plains that might be vulnerable to this type of retreat and calving,” Dr Oshawat added.

But other researchers disputed the study’s results.

The debate revolves around the location of the “grounding line” or “grounding zone” – where the glacier loses contact with the sea floor and begins to float into the ocean.

“This new study provides a tantalizing glimpse into what could be the fastest rate of retreat ever observed in modern Antarctica,” said Dr. Fraser Christie, glaciologist and senior Earth observation specialist at Airbus Defense and Space.

“But there is significant disagreement within the glaciological community about the exact location of the grounding line for Hectoria Glacier, because it is very difficult to obtain accurate records from radar satellites in this fast-flowing region,” he added.

The location of the grounding line may seem trivial, but it is important to determine whether the change is truly unprecedented.

“If this part of the ice sheet is actually floating [rather than resting on the seabed]Dr Christine Batchelor, senior lecturer in physical geography at Newcastle University, said: “The important thing is that the icebergs broke off from the ice shelf, which is a much less unusual behaviour.”

She added: “I think the proposed mechanism and rate of retreat is reasonable in Antarctic ice-flat regions, but because of the uncertainty about the location of the grounding zone in Hectoria, I am not completely convinced that it has been observed here.”

But there is little debate that the fragile white continent – ​​once thought to be largely immune to the effects of global warming – is now changing before our eyes.

Anna Hogg, professor of Earth observation at the University of Leeds, said: “While we disagree about the process that led to this change in Hectoria, we are in complete agreement that the changes in the polar regions are frighteningly rapid, faster than we expected even a decade ago.”

“We must collect more data from satellites, so we can better monitor and understand why these changes occur and what their effects are [for sea-level rise]”.

Additional reporting by the Visual Journalism team