Rapid Antarctic glacier retreat sparks scientific ‘whodunnit’

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

Researchers found that the Hectoria Glacier retreated more than 8 km (5 miles) in just two months at the end of 2022.

The authors believe this may be the first modern example of a process in which a glacier front lying on the seafloor rapidly destabilizes.

But other scientists argue that this part of the glacier was actually floating in the ocean – so the changes, while impressive, are not that unusual.

Floating tongues of glaciers extending out to sea, called ice shelves, are much more prone to collapse than glacier fronts resting on the seafloor.

This is because they are easier to corrode under warm water.

That Hectoria has undergone enormous changes is not in dispute. From January 2022 to March 2023, its front retreated approximately 25 km (16 mi), according to satellite data.

But uncovering the reasons is like a detective mystery, according to the study's lead author Naomi Ochwat, a postdoctoral researcher at the University of Colorado Boulder and a postdoctoral fellow at the University of Innsbruck.

The case began back in 2002 with the extraordinary collapse of the Larsen B ice shelf on the eastern 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 effectively contained the Hectoria Glacier. Without this, Hectoria's movement accelerated, and the glacier thinned.

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

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

This was followed by further loss of floating ice in front of Hectoria as large flat-topped icebergs calved or “calved” and the ice behind accelerated and thinned.

There is nothing unusual about this. Iceberg calving is a natural part of ice sheet behavior, even though it is caused by human activity. climate change makes the loss of ice shelves much more likely.

What was unprecedented, the authors say, was what happened in late 2022 when they suggested that the front of the glacier was “grounded” – resting on the seafloor rather than floating.

In just two months, Hectoria retreated 8.2 km. According to a study published in the journal Nature, this would be almost ten times faster than any previously recorded glacier. Nature.

According to the authors, this unusual change may have occurred due to an ice plain—a relatively flat area of ​​rock on which a glacier rests lightly.

They argue that the rising forces of ocean water can “lift” thinning ice almost immediately, causing icebergs to calve and the glacier to rapidly retreat.

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

“The circumstances may be a little special, but this rapid retreat shows us what can happen elsewhere in Antarctica, where glaciers ground down slightly and sea ice loses its grip,” he added.

What makes this idea even more enticing is that this process has never been observed in the modern world, the authors say. But seabed markings suggest that this may have triggered the rapid loss of ocean ice in Earth's past.

“What we're seeing in Hectoria is a small glacier, but if something similar happens in other areas of Antarctica, it could play a much larger role in the rate of sea level rise,” Dr Coverage said.

This may include Thwaites – 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 will be important to understand whether there are other areas of the ice plains that may be susceptible to such retreat and calving,” Dr. Coverage added.

But other researchers have disputed the study's findings.

The controversy surrounds the position of the “grounding line” or “grounding zone” – where the glacier loses contact with the seabed and begins to float in the ocean.

“This new study provides a tantalizing insight into what may be the fastest retreat rate 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 in the glaciological community about the exact location of the Hectoria Glacier grounding line because it is very difficult to obtain accurate data from radar satellites in this fast-flowing region,” he added.

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

“If this piece of ice sheet really floated [rather than resting on the seabed]Instead, it will culminate in icebergs breaking off from the ice shelf, which is much less unusual behavior,” said Dr Christine Batchelor, senior lecturer in physical geography at Newcastle University.

“I think the proposed mechanism and rate of retreat are plausible in Antarctic ice plain conditions, but due to the uncertainty of where the Hectoria landing zone was located, I am not entirely convinced that it was observed here,” she added.

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.

“While we don't agree on the process causing these changes in Hectoria, we absolutely agree that changes in the polar regions are happening alarmingly quickly, faster than we expected even a decade ago,” said Anna Hogg, professor of Earth observation at the University of Leeds.

“We need to collect more data from satellites so we can better monitor and understand why these changes are happening and what their consequences are. [for sea-level rise]”

Additional reporting from the Visual Journalism team