The R/V Nathaniel B. Palmer photographed from a drone on the ice front of Thwaites Glacier in February 2019. Credit: Alexandra Mazur/University of Gothenburg
Faster in the past: New seafloor images, the highest resolution of any taken from the West Antarctic Ice Sheet, improve understanding of Thwaites Glacier retreat.
At times in the past, the massive Thwaites Glacier has retreated even faster than it is today, raising concerns about its future.
The Thwaites Glacier in West Antarctica, also known as the Doomsday Glacier, has been an elephant in the room for scientists trying to make predictions about global sea level rise.
This huge ice stream is already in a phase of rapid retreat (a “collapse” when viewed on geologic time scales). This has led to widespread concern about exactly how much, or how quickly, its ice can be delivered to the ocean.
A 3D-rendered view of depth-colored multibeam bathymetry (shape of the seafloor), collected by Rán across a seafloor ridge, just in front of the Thwaites Ice Shelf. Credit: Alastair Graham/University of South Florida
The potential impact of Thwaites’ retreat is chilling: The complete loss of the glacier and surrounding icy basins could raise sea levels three to ten feet. The glacier is about the size of Florida.
“Thwaites is really holding on with his nails today, and we should expect to see big changes on small timescales in the future, even from one year to the next, once the glacier recedes beyond a shallow ridge in its bed.” . — Robert Larter
A new study, which was published in
“It’s like you’re looking at a tide gauge on the seafloor,” Graham said. “It really amazes me how beautiful the data is.”
Beauty aside, what’s alarming is that the rate of Thwaites’ reversal that scientists have most recently documented is small compared to the faster rates of change in the past, Graham said.
To understand Thwaites’ earlier retreat, scientists analyzed rib-like formations submerged 700 meters (about 2,300 feet or just under half a mile) below the polar ocean and took into account the region’s tidal cycle, as predicted by computer models, to show that a rib must have been formed every day.
Rán, a Kongsberg HUGIN autonomous underwater vehicle, breaks through the sea ice off Thwaites Glacier, after a 20-hour seafloor mapping mission. Credit: Anna Wahlin/University of Gothenburg
Sometime in the last 200 years, during a period of less than six months, the glacier front lost contact with a seafloor ridge and retreated at a rate of more than 1.3 miles per year (2.1 kilometers per year). year). This is double the rate documented using satellites between 2011 and 2019.
“Our results suggest that very fast retreat pulses have occurred in Thwaites Glacier in the last two centuries, and possibly as recently as the mid-20th century,” Graham said.
“Thwaites is really holding on with his nails, and we should expect to see big changes on small timescales in the future, even from one year to the next, once the glacier recedes beyond a shallow ridge in its bed,” said the marine geophysicist. and study co-author Robert Larter of the British Antarctic Survey.
Map of Thwaites Glacier shown in Landsat 8 satellite imagery collected in February 2019. The autonomous underwater vehicle’s mission path is shown in orange. Changes in the positions of the Thwaites Glacier grounding line in the recent past are shown by colored lines. Credit: Alastair Graham/University of South Florida
To collect the images and supporting geophysical data, the research team, which included scientists from the United States, the United Kingdom and Sweden, launched a state-of-the-art orange robotic vehicle loaded with imaging sensors called ‘Rán’ from the R/V Nathaniel B. Palmer during an expedition in 2019.
Rán, which is operated by scientists from the University of Gothenburg in Sweden, embarked on a 20-hour mission that was as risky as it was fortuitous, Graham said. He mapped an area of seafloor the size of Houston in front of the glacier, and he did so under extreme conditions during an unusual summer notable for its lack of sea ice.
This allowed the researchers to access the front of the glacier for the first time in history.
“This was a pioneering study of the ocean floor, made possible by recent technological advances in autonomous ocean mapping and a bold decision by the Wallenberg Foundation to invest in this research infrastructure,” said Anna Wåhlin, a physical oceanographer at the University of Gothenburg which deployed Rán to Thwaites. “The images that Ran collected give us vital information about the processes occurring at the critical junction between the glacier and the ocean today.”
“It really was a once-in-a-lifetime mission,” said Graham, who said the team would like to sample the seafloor sediments directly so they can more precisely date the ridge-like features.
“But the ice closed in on us pretty quickly and we had to leave before we could do that on this expedition,” he said.
THOR scientists Alastair Graham (right) and Robert Larter (left) gaze in awe at the crumbling ice face on the margin of Thwaites Glacier, from the bridge deck of the R/V Nathaniel B. Palmer. Credit: Frank Nitsche
While many questions remain, one thing is for sure: It used to be that scientists thought Antarctica’s ice sheets were sluggish and slow to respond, but that’s simply not true, according to Graham.
“Just a little kick to Thwaites could spark a big response,” he said.
According to the United Nations, approximately 40 percent of the human population lives within 60 miles of the coast.
“This study is part of a collective, interdisciplinary effort to better understand the Thwaites Glacier system,” said Tom Frazer, dean of the USF College of Marine Sciences, “and just because it’s out of sight, we can’t have Thwaites out.” of the mind. This study is an important step forward in providing essential information to inform global planning efforts.”
Reference: “Rapid Retreat of Thwaites Glacier in the Pre-Satellite Era” by Alastair GC Graham, Anna Wåhlin, Kelly A. Hogan, Frank O. Nitsche, Karen J. Heywood, Rebecca L. Totten, James A. Smith, Claus-Dieter Hillenbrand , Lauren M. Simkins, John B. Anderson, Julia S. Wellner, and Robert D. Larter, September 5, 2022, geoscience of nature.
DOI: 10.1038/s41561-022-01019-9
The study was supported by the National Science Foundation and the UK Natural Environment Research Council through the International Thwaites Glacier Collaboration.
The 2019 expedition was the first of a five-year project called THOR, which stands for Thwaites Offshore Research, and also included team members from a sister project called Thwaites-Amundsen Regional Survey and Network Integrating Atmosphere-Ice-Ocean Processes, or TARSAN. .
