The R/V Nathaniel B. Palmer photographed from a drone on the ice front of the Thwaites Glacier in February 2019. Credit: Alexandra Mazur/University of Gothenburg
Faster in the past: New seafloor images – the highest resolution of any taken on the West Antarctic ice sheet – are shaking up understanding of the retreat of the Thwaites Glacier.
At times in its past, the massive Thwaites Glacier retreated even faster than it does today, heightening 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 of global sea level rise. world.
This massive ice flow is already in a phase of rapid retreat (a “collapse” on a geological time scale). This has led to widespread concern over exactly how much or how quickly it can give up its ice to the ocean.
A 3D view of depth-colored multibeam bathymetry (shape of the seafloor) collected by Rán on 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 frightening: a total loss of the glacier and surrounding icy basins could raise sea levels three to 10 feet. The glacier is about the size of Florida.
“Thwaites is really holding today by its fingernails, and we should expect to see big changes on small time scales in the future – even from year to year – once the glacier retreats to the beyond a shallow ridge in its bed.” — Robert Larter
A new study published in Nature Geoscience is a monthly peer-reviewed scientific journal published by the Nature Publishing Group that covers all aspects of the Earth sciences, including theoretical research, modeling, and fieldwork. Other related work is also published in fields that include atmospheric sciences, geology, geophysics, climatology, oceanography, paleontology, and space science. It was established in January 2008.
” data-gt-translate-attributes=”[{” attribute=””>Nature Geoscience on September 5, adds cause for concern. For the first time, scientists mapped in high-resolution a critical area of the seafloor in front of the glacier, providing them with a window into how fast Thwaites retreated and moved in the past. The research was led by marine geophysicist Alastair Graham at the University of South Florida’s College of Marine Science.
The stunning imagery reveals geologic features that are new to science, and also provides a kind of crystal ball to see into Thwaites’ future. In people and ice sheets alike, past behavior is key to understanding future behavior.
The research team documented more than 160 parallel ridges that were created, like a footprint, as the glacier’s leading edge retreated and bobbed up and down with the daily tides.
“It’s like looking at a tide gauge on the seabed,” Graham said. “It’s truly mind-blowing how beautiful the data is.”
Beauty aside, what’s alarming is that Thwaites’ rate of decline that scientists have documented more recently is small compared to the fastest rates of change in its past, Graham said.
To understand Thwaites’ past retreat, scientists analyzed submerged rib-like formations 700 meters (about 2,300 feet or just under half a mile) below the polar ocean and considered the cycle of the region’s tides, as predicted by computer models, to show that a coast must have been formed each day.
Rán, a Kongsberg HUGIN autonomous underwater vehicle, among the sea ice in front of the Thwaites Glacier, after a 20-hour seafloor mapping mission. Credit: Anna Wåhlin/University of Gothenburg
At some point in the past 200 years, over a span of 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). This is double the rate documented using satellites between 2011 and 2019.
“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,” Graham said.
“Thwaites is really hanging on to his nails today, and we should expect to see big changes on small time scales in the future – even from year to year – once the glacier settles. will retreat past a shallow ridge in its bed,” the marine geophysicist said. 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 path of the autonomous underwater vehicle mission is shown in orange. Changes in the positions of the Thwaites Glacier grounding lines in the recent past illustrated 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, United Kingdom and Sweden, launched a state-of-the-art orange robotic vehicle tasked with imaging sensors called “Rán” from the R/V Nathaniel B. Palmer during an expedition in 2019.
Rán, which is operated by scientists at the University of Gothenburg in Sweden, embarked on a risky and fortuitous 20-hour mission, Graham said. He mapped an area of seafloor the size of Houston in front of the glacier – and did it in extreme conditions during an unusual summer notable for its lack of sea ice.
This allowed 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 said Anna Wåhlin, a physical oceanographer at the University of Gothenburg. deployed Rán to Thwaites. “The images Ran collected give us essential insight into the processes taking place today at the critical glacier-ocean junction.”
“It was truly a once-in-a-lifetime mission,” said Graham, who said 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.
THOR scientists Alastair Graham (right) and Robert Larter (left) gaze in awe at the crumbling ice face of the Thwaites Glacier margin, from the bridge deck of the R/V Nathaniel B. Palmer. Credit: Frank Nitsche
While many questions remain, one thing is certain: Scientists once 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 lead to a big response,” he said.
According to the United Nations, approximately 40% 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 Science, “and just because it’s out of sight, we don’t We cannot have Thwaites out of mind. This study is an important step forward in providing critical information to inform global planning efforts.
Reference: “Rapid retreat of the 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 geoscience.
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. .