The recent rapid retreat of an Antarctic glacier could be unprecedented, a new study suggests, a finding which could have major implications for future sea-level rise.
The researchers found that Hektoria Glacier retreated by more than 8 km (5 miles) in just two months in late 2022.
The authors believe it could be the first modern example of a process where the front of a glacier resting on the seabed rapidly destabilises.
But other scientists argue that this part of the glacier was actually floating in the ocean – so while the changes are impressive, they are not so unusual.
Floating tongues of glaciers extending into the sea – called ice shelves – are much more prone to breaking up than glacier fronts resting on the seabed.
That Hektoria has undergone huge change is not contested. Its front retreated by about 25 km (16 miles) between January 2022 and March 2023, satellite data shows.
But unravelling the causes is like a 'whodunnit' mystery, according to study lead author Naomi Ochwat, research affiliate at the University of Colorado Boulder and post-doctoral researcher at the University of Innsbruck.
The case began way back in 2002 with the extraordinary collapse of an ice shelf called Larsen B in the eastern Antarctic Peninsula. About 3250 sq km (1250 sq miles) of ice shelf was lost, roughly the size of Cambridgeshire or Gloucestershire.
Larsen B had been effectively holding Hektoria Glacier back. Without it, Hektoria's movement sped up and the glacier thinned.
But the bay vacated by the ice shelf was eventually filled with sea-ice fastened to the seabed, helping to partly stabilise Hektoria. That was until early 2022, when the sea-ice broke up.
What followed was further loss of floating ice from the front of Hektoria, as large, flat-topped icebergs broke off or 'calved', and the ice behind sped up and thinned.
This extraordinary change, the authors say, could be thanks to an ice plain - a relatively flat area of bedrock on which the glacier lightly rests.
Upward forces from the ocean water could lift the thinning ice essentially all at once, they argue - causing icebergs to break off and the glacier to retreat in quick time.
What we see at Hektoria is a small glacier, but if something like that were to happen in other areas of Antarctica, it could play a much larger role in the rate of sea-level rise.
But other researchers have contested 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 starts to float in the ocean.
The location of the grounding line may sound trivial, but it is crucial to determine whether the change was truly unprecedented. If this section of the ice sheet was in fact floating, the punchline would instead be that icebergs calved from an ice shelf, which is much less unusual behaviour.
While we disagree about the process driving this change at Hektoria, we are in absolute agreement that the changes in the polar regions are scarily rapid, quicker than we expected even a decade ago.
