The rapid retreat of polar ice is drawing intense attention as scientists map the seafloor beneath the Thwaites Glacier, a massive ice stream the size of England, located in West Antarctica. New high-resolution images indicate strong thinning and a potential for substantial sea-level rise, with estimates suggesting the loss of this glacier and its surrounding basins could lift sea levels by one to three meters. The finding was highlighted in a Nature Geoscience publication.
Researchers warn that understanding the speed and extent of ice loss is crucial for predicting future changes to coastlines around North America and beyond.
The study, led by marine geophysicist Alastair Graham from the University of South Florida’s School of Marine Sciences, presents a landmark at-seafloor map in front of the glacier. For the first time, scientists reveal how Thwaites retreated and advanced through geological history, offering a clearer window into its behavior under changing ocean conditions.
These striking underwater images reveal features previously unseen by science and serve as a kind of predictive tool for the glacier’s near future. In both ice sheets and natural systems, past behavior informs expectations for what comes next.
The team documented more than 160 parallel ridges formed as the glacier’s edge retreated and rose with the tides. Graham describes the view as if they were watching a tide gauge resting on the seafloor, noting the data’s striking beauty as well as its alarming implications.
The observed retreat rate is only one part of a larger story, as recent measurements show retreat pulses that historically outpace the most recent figures. This places a premium on understanding the timing and magnitude of future changes in the Thwaites system.
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To decipher Thwaites’ history, researchers analyzed rib-like formations lying about 700 meters below the polar ocean surface and accounted for tidal cycles. Computer models suggest daily formation of such ridges, reflecting ongoing interactions between the glacier front and the ocean floor.
In the past two centuries, more than once the glacial front lost contact with a seafloor ridge and surged forward at speeds exceeding two kilometers per year. Between 2011 and 2019, the rate nearly doubled compared with satellite-era estimates.
Graham notes that rapid retreat pulses appear to have occurred in the last two centuries and possibly in the mid-20th century as well.
“We expect big changes from year to year”
Robert Larter, a marine geophysicist with the British Antarctic Survey and a co-author, adds that the glacier is unlikely to keep pace with every shallow ridge in its bed. He predicts notable shifts on short time scales ahead as the ice interacts with deeper features in its bed.
To collect the imagery and supplement the geophysical data, the team used an advanced orange robotic vehicle equipped with imaging sensors, named Rán, launched from the Nathaniel B. Palmer during a 2019 expedition.
The mission, led by scientists from the University of Gothenburg in Sweden, mapped a seafloor area as large as the city of Houston in front of the glacier. The journey took place under extreme conditions, including a rare summer without sea ice, enabling access to the glacier’s front for the first time in history.
Anna Wahlin, a physical oceanographer at the University of Gothenburg, describes the study as a pioneering effort enabled by cutting-edge autonomous ocean mapping and strong support from research funding bodies. The images collected by Rán provide crucial insight into the ongoing processes at the critical boundary where the glacier meets the ocean.
“This was a once-in-a-lifetime task,” says Graham, noting the aim to directly sample seafloor sediments to date the ridge features more accurately. The team faced difficult conditions but pressed on to enhance the understanding of a system that holds global significance.
While many questions remain, scientists emphasize a shift in thinking. Antarctic ice sheets were once thought slow to react, but recent work shows they can respond quickly under certain oceanic conditions. The United Nations highlights that a significant share of the world’s population lives near coastlines, underscoring the importance of this research for coastal planning and resilience.
Tom Frazer, dean of the USF School of Marine Sciences, characterized the project as part of a broader, interdisciplinary effort to illuminate the Thwaites Glacier system and to provide actionable information for decision makers.
Citation of the study: Nature Geoscience, 2022 edition.
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