At times in its past, the massive Thwaites Glacier retreated even faster than it does today, raising concerns about its future – ScienceDaily

The Thwaites Glacier in West Antarctica – the size of Florida – has been an elephant in the room for scientists trying to make predictions of global sea level rise.

This massive ice flow is already in a phase of rapid retreat (a “collapse” when observed on geologic timescales), prompting widespread concern about exactly how much or how quickly it may surrender its ice to the ocean.

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.

A new study in nature geoscience led by marine geophysicist Alastair Graham of the College of Marine Science at the University of South Florida adds cause for concern. For the first time, scientists have mapped a critical area of ​​the seafloor in front of the glacier in high resolution, giving them a window into 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 Thwaites’ future. In humans 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 fell 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, the team analyzed submerged rib-like formations 700 meters (just under half a mile) below the polar ocean and factored in the tidal cycle for the region, as predicted by computer models, to show that a rib must have been formed each day.

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) – twice 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 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,” the marine geophysicist said. and study co-author Robert Larter of the British Antarctic Survey.

To collect 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 sensors imagery called “Rán” from R/V Nathaniel B. Palmer during an expedition in 2019.

Rán, operated by scientists from the University of Gothenburg in Sweden, embarked on a risky and fortuitous 20-hour mission, Graham said. He mapped an area of ​​the seabed in front of the Houston-sized glacier – and did it in extreme conditions during an unusual summer notable for its lack of sea ice.

This gave scientists access to 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.

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, Graham said.

“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 USF College of Marine Science Dean Tom Frazer, “and just because it’s out of sight, we can’t have Thwaites out.This study is an important step forward in providing critical information to inform global planning efforts.

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. .


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