R/V Nathaniel B. Palmer photographed from a drone on the Thwaites Glacier ice front in February 2019. Credit: Alexandra Mazur/ University of Gothenburg
Faster in the Past: New seafloor images – the highest resolution of those from the West Antarctic Ice Sheet – are upending understanding of the Thwaites Glacier retreat.
In times past, the massive Thwaites Glacier’s retreat was faster than it is today, raising concerns for 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 of global sea level rise.
This massive ice stream is already in a rapid retreat (a “collapse” on geological time scales). This has led to widespread concern about exactly how much or how fast it could release its ice into the ocean.
A 3D rendered view of multibeam bathymetry colored by depth (seafloor shape) collected by Rán along 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 grisly: complete loss of the glacier and surrounding icy basins could raise sea level from three meters to ten meters. The glacier is the size of Florida.
“Thwaites is really clinging to his claws today, and as he retreats beyond a shallow ridge in the glacier bed, we should expect to see big changes on small timescales in the future – even from one year to the next. Robert Larter
A new study published
“It’s like looking at a tide gauge on the seafloor,” Graham said. “It really blows my mind how beautiful the data is.”
Beauty aside, what’s alarming is that the Thwaites retracement rate that scientists have documented more recently is small compared to the fastest rates of change in the past, Graham said.
To understand Thwaites’ past retreat, the scientists analyzed rib-like formations that lie 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 computer models predicted. Show that a rib should form every day.
In the morning, after a 20-hour mission mapping the seafloor, among the sea ice in front of the Thwaites Glacier, the Kongsberg HUGIN autonomous underwater vehicle. Credit: Anna Wåhlin / University of Gothenburg
At one point in the last 200 years, for less than six months, the front of the glacier lost contact with the seafloor ridge and retreated at a rate of more than 2.1 kilometers per year (1.3 miles per year). This is double the rate documented using satellites between 2011 and 2019.
“Our results show that very rapid retreating pulses have occurred on the Thwaites Glacier in the last two centuries and possibly the mid-20th century,” Graham said. Said.
“Thwaites is really clinging to his claws today, and as he retreats beyond a shallow ridge in the glacier bed, we should expect to see big changes on small timescales in the future – even from one year to the next,” the sailor said. geophysicist and co-author Robert Larter of the British Antarctic Survey.
Map of Thwaites Glacier shown in Landsat 8 satellite images collected in February 2019. The mission route of the autonomous underwater vehicle is shown in orange. Changes in the Thwaites Glacier ground line locations in the recent past are indicated by colored lines. Credit: Alastair Graham/University of South Florida
The research team, which includes scientists from the US, UK and Sweden, has launched a state-of-the-art orange robotic instrument from the US equipped with imaging sensors called ‘Rán’ to collect images and supporting geophysical data. R/V Nathaniel B. Palmer during an expedition in 2019.
Run by scientists at the University of Gothenburg in Sweden, Rán embarked on a 20-hour mission that was as risky as it was accidental, Graham said. He mapped the seafloor in front of the glacier, about the size of Houston, and did so in extreme conditions during an unusual summer notable for the lack of sea ice.
This allowed researchers to access the glacial front for the first time in history.
“This was a pioneering study of the ocean floor made possible by the latest technological advances in autonomous ocean mapping and the Wallenberg foundation’s bold decision to invest in this research infrastructure,” said physical oceanographer Anna Wåhlin from the University of Gothenburg. Deployed Sabah at Thwaites. “The images that Ran collected give us vital information about the processes occurring today at the critical juncture between the glacier and the ocean.”
“This was truly a once-in-a-lifetime task,” said Graham, who said the team wanted to directly sample seafloor sediments to be able to more accurately date ridge-like features.
“But the ice was very quickly on us and this time we had to leave before we could do that,” he said.
THOR scientists Alastair Graham (right) and Robert Larter (left) admire the shattering ice face of the shore of the Thwaites Glacier from the bridge deck of R/V Nathaniel B. Palmer. Credit: Frank Nitsche
While many questions remain, one thing is certain: Scientists used to think the Antarctic ice sheets were slow and slow to respond, but according to Graham, that’s not true.
“A little kick to Thwaites could lead to a big backlash,” he said.
According to the United Nations, roughly 40 percent of the human population lives 60 miles from the coast.
“This work is part of an interdisciplinary collective effort to better understand the Thwaites Glacier system,” said Tom Frazer, dean of the USF College of Marine Sciences. It is an important step in providing the necessary information.”
Reference: “The 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. Nature Geology.
DOI: 10.1038/s41561-022-01019-9
The work was supported by the National Science Foundation and the UK’s 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 Research and Network Integrating Atmosphere-Ice-Ocean Processes, or TARSAN. .
