Maximum concern in the face of the melting of an icy mass as large as the United Kingdom
The melting of the poles is accelerating at a breakneck pace. The huge Thwaites Glacier, a massive ice stream the size of the UK and located in the Antarctica Occidental, is already in a phase of rapid retreat, according to new images of the seafloor taken with the highest resolution so far. A total loss of the glacier and surrounding ice basins could raise sea level by 1 to 3 metersas published by the researchers in the journal ‘Nature Geoscience’.
This rapid retreat has prompted widespread concern about exactly how much, or how quickly, its ice may yield to the ocean.
The new study, led by marine geophysicist Alastair Graham of the University of South Florida School of Marine Sciences, add cause for concern. For the first time, scientists have mapped in high resolution a critical area of the seafloor in front of the glacier that allows them to understand how quickly Thwaites retreated and moved in the past.
The stunning images show geological features new to science, and also provide a kind of crystal ball to see into Thwaites’ future. In both people and ice sheets, past behavior is key to understanding future behavior.
The team documented more than 160 parallel ridges that were created, like an imprint, as the leading edge of the glacier retreated and rose. and went down with the daily tides. “It’s like you’re looking at a tide gauge at the bottom of the sea,” Graham explains. “I’m really amazed at the beauty of the data.”
Beauty aside, what’s alarming is that the rate of Thwaites’ retreat that scientists have documented most recently is small compared to the faster rates of change in its past, Graham said.
To understand Thwaites’s past retreat, the team analyzed the submerged rib-like 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 ‘rib’ must have formed each day.
Sometime in the last 200 years, in a duration of less than six months, the glacier front lost contact with a seafloor ridge and retreated at a rate of more than 2.1 kilometers per yeardouble 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,” says Graham.
“We expect to see big changes from year to year”
“Thwaites is barely holding up today, and we expect to see big changes on small time scales in the future – even from year to year – once the glacier recedes beyond a shallow ridge in its bed,” adds marine geophysicist and study co-author Robert Larter of the British Antarctic Survey.
To collect the imagery 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 imaging sensors called ‘Rán’ from the R/V Nathaniel B. Palmer during an expedition in 2019.
Rán, operated by scientists from the University of Gothenburg, Sweden, embarked on a 20-hour mission that was “as risky as it was serendipitous,” according to Graham. The team mapped an area of seafloor in front of the glacier the size of Houston, and it did so under extreme conditions during an unusual summer, characterized by the absence of sea ice. This allowed them to access the front of the glacier for the first time in history.
“This is a pioneering study of the ocean floor, made possible by recent technological advances in autonomous ocean mapping and the Wallenberg Foundation’s bold decision to invest in this research infrastructure,” said Anna Wahlin, a physical oceanographer at the University of Gothenburg– The images that the Rán has collected give us a vital insight into the processes that occur at the critical junction between the glacier and the ocean today.”
“It was really a once-in-a-lifetime mission,” says Graham, who says the team would like to sample the seafloor sediments directly so they can more accurately date the ridge features. “But the ice closed in on us very quickly and we had to leave before we could do that on this expedition.
Although many questions remain, one thing is certain and that is that before scientists used to think the Antarctic ice sheets were lazy and slow to respond, but that’s just not trueGraham indicates.
According to the United Nations, approximately 40% of the human population lives within 100 kilometers 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 School of Marine Sciences, “and just because it’s out of sight, we can’t have Thwaites out of mind. This study is an important step in providing essential information to inform global planning efforts.”
Reference study: https://www.nature.com/articles/s41561-022-01019-9
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