The R/V Nathaniel B. Palmer photographed by a drone on the Thwaites Glacier ice front in February 2019. Image credit: Alexandra Mazur/University of Gothenburg When viewed in geologic timescales, this massive ice stream is already in a stage of rapid retreat known as “collapse,” which has raised many questions about how much ice it will eventually lose to the ocean, and how quickly. The effects of Thwaites’ retreat could be terrifying: if the glacier and surrounding ice basins were to disappear completely, sea levels could rise by three to ten feet. The concern is heightened by a recent study published in Nature Geoscience led by marine geophysicist Alastair Graham of the College of Marine Science at the University of South Florida. The floor in front of the glacier was imaged in vital high resolution for the first time, providing researchers with a window into how quickly the Thwaites advanced and retreated in the past. The fascinating material offers a kind of crystal ball into which to look into the future of Thwaites and reveals aspects of geology that are new to science. Understanding past behavior is essential to predicting future behavior in humans and ice sheets. The crew recorded more than 160 parallel ridges left behind when the front edge of the glacier receded and swayed with the daily tides. It’s like looking at a tide gauge at the bottom of the sea. It blows my mind how beautiful the data is. Alastair Graham, Marine Geophysicist, College of Marine Science, University of South Florida Graham added that despite its beauty, Thwaites is worrisome because the rate of retreat scientists recently discovered is slow compared to the faster rates of change in its past. Scientists examined the rib-like structures 700 meters (just under half a mile) below the Arctic Ocean to understand Thwaites’ previous retreat. They also looked at the region’s tidal cycle, as predicted by computer models, to prove that one side should develop each day. The front of the glacier lost contact with a ridge on the sea floor sometime in the last 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). it is double the rate observed by satellites between 2011 and 2019. “Our results suggest that pulses of very rapid retreat have occurred on Thwaites Glacier over the past two centuries, and possibly as recently as the mid-20th century,” Graham said. “Thwaites is currently holding on by its claws, and we should expect to see big changes over short periods of time in the future – even from one year to the next – once the glacier retreats beyond a shallow ridge in its bed.” said Robert Larter. a marine geophysicist and co-author of the British Antarctic Survey study. The team, which includes researchers from the United States, the United Kingdom, and Sweden, deployed a cutting-edge orange robotic vehicle named “Rán” from the R/V Nathaniel B. Palmer during a 2019 mission to collect the images and accompanying geophysical data. According to Graham, Rán – led by researchers at the University of Gothenburg in Sweden – embarked on a 20-hour journey that was both dangerous and lucky. He did so in harsh conditions during an unusual summer notable for the absence of sea ice, mapping an area of the seabed in front of the glacier the size of Houston. This enabled scientists to reach the front of the glacier for the first time. “This was a ground-breaking 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 Anna Wåhlin, a physical oceanographer from the University of Gothenburg. developed Rán at Thwaites. “The images collected by Ran give us vital information about the processes occurring at the critical junction between the glacier and the ocean today,” said Wåhlin. It was truly a once in a lifetime mission. Alastair Graham, Marine Geophysicist, College of Marine Science, University of South Florida Graham said that to more precisely date the ridge-like features, researchers would like to directly sample the bottom sediments. “But the ice closed in on us very quickly and we had to leave before we could do that on this mission,” he said. There are still many unanswered concerns, but one thing is certain, according to Graham: The Antarctic ice sheets are not at all what researchers thought. “Just a small kick to Thwaites could lead to a big response,” he said. According to the United Nations, about 40% of people live within 60 miles of the coast. “This study is part of a multidisciplinary collaborative effort to better understand the Thwaites Glacier system, and just because it’s not visible, we can’t keep Thwaites out of our minds. This study is an important step forward in providing key information to inform global planning efforts,” said Tom Frazer, dean of the USF College of Marine Science. The National Science Foundation and the UK’s Natural Environment Research Council funded the project through the Thwaites International Glacier Collaboration.
Journal Reference:
Graham, AGC, et al. (2022) Rapid retreat of Thwaites Glacier in the pre-satellite era. Geoscience of nature. doi.org/10.1038/s41561-022-01019-9. Source:
