Thwaites glacier is a growing concern | Polarjournal
The Thwaites Glacier in West Antarctica is currently undergoing dramatic changes. In 2019, two interdisciplinary research teams deployed an autonomous underwater vehicle (AUV) from the U.S. research icebreaker R.V. Nathaniel B. Palmer deployed at the ice edge to study the glacier’s history and understand how it is affected by the ocean. Photo: Alexandra Mazur, University of Gothenburg/Rob Larter, British Antarctic Survey

The Thwaites Glacier in West Antarctica, colloquially known as the “Doomsday Glacier” because of its high risk of collapse, is increasingly worrying researchers. Already, its ice shelf is losing mass at a rapid pace, and new findings suggest it is hanging by a thread. The new research shows that it has the potential to retreat even faster in the coming years.For global sea levels, the collapse would mean a massive rise. The new study was published in the journal Nature Geoscience.

If the Thwaites Glacier ice shelf were to collapse, this alone would release so much ice that sea levels worldwide could rise by up to 65 centimeters. However, together with Pine Island Glacier, it acts as a kind of brake on the much larger West Antarctic Ice Sheet. If the two glaciers can no longer fulfill this task one day, the sea level will rise again by more than one meter.

In geological time scales, a collapse of Thwaites Glacier is already taking place, which is why there is great concern among scientists. To learn more about its past evolution, a team of researchers from the University of South Florida, the University of Gothenburg, the British Antarctic Survey and other institutions has mapped the seafloor off the glacier in high resolution for the first time. Using images taken by the underwater robot “Ran,” they were able to determine how fast the glacier retreated in the past.

The University of Gothenburg’s Kongsberg HUGIN AUV “Ran” undertook 20-hour deployments at two sites, combining seafloor mapping and mid-water column profiling and sampling programs. Photo: Graham et al. 2022

The team documented more than 160 parallel ridges at a depth of about 700 meters, created like a footprint as the glacier’s grounding line retreated and moved up and down with the daily tides. Computer models calculated that such a “rib” must have formed every day.

“It’s as if you are looking at a tide gauge on the seafloor,” says lead author Dr. Ali Graham of the University of Florida. “It really blows my mind how beautiful the data are.”

However, it is alarming that recent rates of glacier retreat documented by researchers are low compared to the fastest rates of change in the past, Graham said. They suspect that the current phase will be followed by a period of even more rapid retreat.

A side-scan sonar shows the “ridges” in the seafloor discovered by Ran. Photo: Ali Graham

Sometime in the last 200 years, the glacier front lost contact with the seafloor over a period of less than six months, retreating at a rate of more than 2.1 kilometers per year – twice the rate documented by satellites between 2011 and 2019.

“Our results suggest that pulses of very rapid retreat have occurred at Thwaites Glacier in the last two centuries, and possibly as recently as the mid-20th Century,” Graham explains.

3D view of high-resolution multibeam echosounder bathymetry acquired by Ran. Image: Graham et al. 2022

Dr. Robert Larter, a marine geophysicist at the British Antarctic Survey and co-author of the study, adds, “Thwaites is really holding on today by its fingernails, and we should expect to see big changes over small timescales in the future – even from one year to the next – once the glacier retreats beyond a shallow ridge in its bed.”

Although many questions remain unanswered, one thing is now certain: Scientists used to think the Antarctic ice sheets were sluggish and slow to respond, but that’s simply not true, Graham said. “Just a small kick to Thwaites could lead to a big response.”

“This was a pioneering study of the ocean floor, made possible by recent technological advancements in autonomous ocean mapping and a bold decision by the Wallenberg Foundation to invest into this research infrastructure. The images Rán collected give us vital insights into the processes happening at the critical junction between the glacier and the ocean today,” says Anna Wåhlin, physical oceanographer at the University of Gothenburg and co-author of the study.

Julia Hager, PolarJournal

Link to the study: Graham, A.G.C., Wåhlin, A., Hogan, K.A. et al. Rapid retreat of Thwaites Glacier in the pre-satellite era. Nat. Geosci. (2022).

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