Seafloor images shed new light on retreating Thwaites Glacier

Seabed images shed new light on retreating Thwaites Glacier (Anna Wahlin/University of Gothenburg)

Scientists have mapped a critical area of ​​the seafloor in front of the Thwaites Glacier in West Antarctica in high resolution for the first time, giving them a window into how fast it retreated and moved in the past.

The glacier has been an important consideration for scientists trying to make predictions about global sea level rise.

This massive ice flow is already in a phase of rapid retreat, prompting widespread concern about exactly how much or how fast it may be giving up its ice to the ocean.

Experts suggest that a total loss of Thwaites and the surrounding icy basins could raise sea levels by three to 10 feet.

Thwaites is really holding on today by its fingernails, and we should expect to see big changes on small time scales in the future…

Robert Larter, British Antarctic Survey

However, the study indicates that the glacier could experience large changes on small timescales in the future.

Alarmingly, analysis of the new images indicates that Thwaites’ rate of recoil that scientists have documented more recently is small compared to the fastest rates of change in its past.

Marine geophysicist and study co-author Robert Larter of the British Antarctic Survey said: “Thwaites is really holding on today by his fingernails, and we should expect to see big changes on small time scales at the future – even from year to year – once the glacier retreats past a shallow ridge in its bed.

The images show geological features new to science and also provide a kind of crystal ball to see the future of the glacier.

The researchers documented more than 160 parallel ridges that were created, like an imprint, as the leading edge of the glacier retreated and rose and fell with the daily tides.

Marine geophysicist Alastair Graham, from the College of Marine Science at the University of South Florida, said: ‘It’s like looking at a tide gauge on the seabed.

“It’s truly mind-blowing how beautiful the data is.”

The team analyzed formations 700 meters below the polar ocean and took into account the region’s tidal cycle – as predicted by computer models, to show that a coast must have formed every day.

They suggest that at some point in the last 200 years, in less than six months, the glacier front lost contact with a seabed ridge and retreated at a rate of more than 2.1 kilometers. per year (1.3 miles per year) – twice the rate documented using satellites between 2011 and 2019.

Dr Graham said: “Our results suggest that very rapid retreat pulses have occurred at Thwaites Glacier over the past two centuries, and possibly as recently as the mid-20th century.”

To collect the images and supporting geophysical data, the team – which included scientists from the US, UK and Sweden – launched a state-of-the-art orange robotic vehicle loaded with sensors to imagery called Ran during an expedition in 2019.

Managed by scientists from the University of Gothenburg in Sweden, Ran embarked on a 20-hour mission to map an area of ​​the seafloor in front of the Houston-sized glacier – and did it in extreme conditions at the during an unusual summer notable for its lack of sea ice.

Anna Wahlin, physical oceanographer from the University of Gothenburg who deployed Ran to Thwaite, said: “This was a pioneering study of the ocean floor, made possible by recent technological advances in autonomous mapping oceans and a bold decision by the Wallenberg Foundation to invest in this research infrastructure.

“The images Ran collected give us essential insight into the processes taking place today at the critical glacier-ocean junction.”

Dr Graham said it was a “once in a lifetime mission”, adding that the team would like to sample seafloor sediments directly so they can date the ridge-like features more precisely.

“But the ice closed in on us pretty quickly and we had to leave before we could do that on this expedition,” he said.

He explained that scientists used to think Antarctica’s ice sheets were slow and slow to respond, but that’s simply not true.

The results are published in the journal Nature.

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