Faster in the Past: New seafloor images of West Antarctic Ice Sheet upend understanding of Thwaites Glacier retreat



For scientists attempting to anticipate the rate of rise in the ocean's surface waters, the Thwaites Glacier in West Antarctica, which is about the size of Florida, has been a major sticking point.

When seen on geological periods, this vast ice stream is already in a phase of rapid retreat, which is known as a "collapse," which has raised a lot of questions about how much ice it will eventually lose to the ocean and how quickly.

The effects of Thwaites' retreat might be terrifying: if the glacier and its surrounding glacial basins completely vanish, sea level could rise by three to ten feet.

Concern is increased by a recent study published in Nature Geoscience that was headed by marine geophysicist Alastair Graham of the College of Marine Science at the University of South Florida. The seafloor in front of the glacier was crucially imaged in high resolution for the first time, providing researchers with a window into how quickly Thwaites advanced and receded in the past.

The breathtaking footage offers a kind of crystal ball to look into Thwaites' future and reveals geologic aspects that are new to science. Understanding previous behavior is essential to predicting future behavior in both humans and ice sheets.

The scientists recorded more than 160 parallel ridges that were formed as the glacier's leading edge retreated and wobbled in response to the tides each day, leaving a footprint-like pattern.

Graham remarked, "It's like staring at a tidal gauge on the seafloor. The beauty of the statistics absolutely astounded me.

Graham added that despite its beauty, Thwaites is troubling because the rate of retreat that scientists have lately discovered is slow compared to the quickest rates of change in its past.

The scientists examined the rib-like structures 700 meters (just under half a mile) beneath the arctic ocean to comprehend Thwaites' previous retreat. They also took into account the region's tidal cycle, as predicted by computer models, to demonstrate that one rib must have formed each and every day.

The front of the glacier lost contact with a ridge on the seafloor somewhere in the past 200 years, and for a period of less than six months, it retreated at a rate of more than 2.1 kilometers per year (1.3 miles per year), which is twice the rate observed by satellites between 2011 and 2019.

As recently as the middle of the 20th century, according to Graham's findings, Thwaites Glacier may have experienced pulses of extremely rapid retreat.

According to marine geophysicist and research co-author Robert Larter of the British Antarctic Survey, "Thwaites is truly hanging on by its fingernails today. We should expect to witness big changes over small durations in the future—even from one year to the next."

The team, which includes researchers from the United States, the United Kingdom, and Sweden, launched a cutting-edge orange robotic vehicle dubbed "Rán" from the R/V Nathaniel B. Palmer during an expedition in 2019 to gather the imagery and accompanying geophysical data.

According to Graham, Rán, which was run by researchers at the University of Gothenburg in Sweden, set off on a 20-hour journey that was both dangerous and fortunate. It did so in harsh conditions during an extraordinary summer remarkable for its absence of sea ice, mapping a region of the seabed in front of the glacier about the size of Houston.                                                                       
For the first time ever, this gave scientists access to the glacier front.

According to Anna Whlin, a physical oceanographer from the University of Gothenburg who deployed Rán at Thwaites, "This was a pioneering study of the ocean floor, made possible by recent technological advancements in autonomous ocean mapping and a bold decision by the Wallenberg foundation to invest into this research infrastructure." The pictures Ran took help us understand the current activities taking place at the crucial intersection of the glacier and the ocean.

The researchers would like to take direct sediment samples from the bottom in order to more precisely date the ridge-like features, which Graham described as "really a once in a lifetime mission."

But on this mission, we had to leave before we could do anything since the ice swiftly surrounded us.

There are still many unanswered concerns, but one thing is certain, according to Graham: The Antarctic ice sheets are not at all what scientists had believed them to be.

He stated, "Just a little kick to Thwaites may cause a major reaction.

About 40 percent of people live within 60 miles of the coast, according to the United Nations.

"Tom Frazer, dean of the USF College of Marine Science, stated that this study is a component of a multidisciplinary effort to better understand the Thwaites Glacier system. "Thwaites cannot be forgotten just because it is out of sight," he added. This study represents a significant advance in the dissemination of crucial data to support efforts at international planning."

Through the International Thwaites Glacier Collaboration, the project was funded by the National Science Foundation and the UK Natural Environment Research Council.

The Thwaites Offshore Research (THOR) project, which has a five-year timeline, was launched with the 2019 expedition. Team members from TARSAN, a related project known as the Thwaites-Amundsen Regional Survey and Network Integrating Atmosphere-Ice-Ocean Processes, also participated.

University of South Florida

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