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Satellite radar data show significant intrusion of seawater beneath that of Antarctica Thwaites Glacierwhich causes the ice to rise and fall.

Using high-resolution satellite radar data, a team of glaciologists led by researchers from the University of California, Irvine, has found evidence of high-pressure warm seawater entering many kilometers beneath the grounded ice of the Thwaites Glacier in West Antarctica. This glacier is often called the “Doomsday Glacier” because of its critical role in potential global sea-level rise and the catastrophic consequences such a rise would have on a global scale. This nickname reflects the glacier’s enormous size and its significant melting rate, which scientists believe could significantly contribute to sea level rise if it collapses or melts completely.

The team, led by the University of California, Irvine, said that widespread contact between ocean water and ice – a process repeated in Antarctica and in Greenland – is causing “vigorous melting” and may require a reassessment of global sea-level rise projections . Their research was published on May 20 in Proceedings of the National Academy of Sciences,

Data and observations

Glaciologists rely on data collected from March to June 2023 by the Finnish commercial satellite ICEYE mission. The ICEYE satellites form a ‘constellation’ in polar orbit around the planet, using InSAR – Synthetic Aperture Radar Interferometer – to continuously monitor changes in the Earth’s surface. Many spacecraft passes over a small, defined area produce smooth data results. In the case of this study, it shows the rise, fall and bending of the Thwaites Glacier.

“These ICEYE data provided a long-term series of daily observations closely matching the tidal cycles,” said lead author Eric Rignot, professor of Earth system science at UC Irvine. “In the past, we’ve had some sporadically available data, and with just those few observations, it’s been hard to figure out what’s going on.” When we have a continuous time series and compare it to the tidal cycle, we see seawater coming in at high tide and retreating, and sometimes going further up under the glacier and being trapped. Thanks to ICEYE, we are beginning to witness these tidal dynamics for the first time.”

Screenshot of a 3D view of the tidal motion of Thwaites Glacier, West Antarctica, recorded by the ICEYE Synthetic Aperture Radar (SAR) radar constellation based on images acquired on 11, 12 and 13 May 2023. Contour levels are bed relief contours at 50 m intervals. Each interferometric fringe color cycle is a 360-degree change in phase, equivalent to a 1.65 cm shift in sight distance on the ice surface. The interferogram is overlaid on a Landsat 9 image acquired in February 2023. In this study, we show that the tidal flexure margin varies by kilometers over the tidal cycle, indicating that pressurized seawater can penetrate beneath ground ice for kilometers and to enhance heat exchange with the base of the glacier. On the right-hand side of the screen, a separate bull’s-eye pattern shows seawater intrusion spreading a further 6 km beyond a protective ridge, indicating that glacier retreat is still ongoing, at a kilometer per year in this critical sector of Antarctica. Credit: Eric Rignot / UC Irvine

Advanced satellite observations

ICEYE Director of Analysis Michael Wollersheim, co-author, said: “Until now, some of nature’s most dynamic processes have been impossible to observe in sufficient detail or frequency to allow us to understand and model them. Observing these processes from space and using radar satellite imagery, which provides InSAR measurements with centimeter-level precision at a daily frequency, marks a significant leap forward.”

Rigneault said the project helped him and his colleagues better understand the behavior of seawater at the base of Thwaites Glacier. He said seawater entering the base of the ice sheet, combined with fresh water generated by geothermal flow and friction, is accumulating and “has to flow somewhere.” Water spreads through natural conduits or collects in cavities, creating enough pressure to lift the ice sheet.

“There are places where the water is almost under the pressure of the overlying ice, so it only takes a little more pressure to push the ice out,” Rigneault said. “The water is then squeezed out enough to lift a column of more than half a mile of ice.”

And it’s not just seawater. For decades, Rigneault and his colleagues have collected evidence of the impact of climate change on ocean currents that push warmer seawater toward the shores of Antarctica and other polar ice regions. Circumpolar deep water is salty and has a lower freezing point. While fresh water freezes at zero degrees Celsiussalt water freezes at minus two degrees, and that small difference is enough to contribute to the “vigorous melting” of the underlying ice, the study found.

Impacts on sea level rise and future research

Co-author Christine Dow, professor in the Faculty of Environment at University of Waterloo in Ontario, Canada, said: “The Thwaites is the most unstable place in Antarctica and contains the equivalent of 60 centimeters of sea level rise. The concern is that we are underestimating the rate at which the glacier is changing, which would be detrimental to coastal communities around the world.

Rigneault said he hopes and expects the results of this project to spur further research into conditions beneath Antarctic ice sheets, exhibitions involving autonomous robots and more satellite observations.

“There’s a lot of enthusiasm from the scientific community to go to these remote, polar regions to collect data and build our understanding of what’s going on, but funding has lagged,” he said. “We’re operating on the same budget in 2024 in real dollars as we were in the 1990s. We need to grow the community of glaciologists and physical oceanographers to tackle these observational problems sooner rather than later, but right now we’re still climbing Mount Everest in tennis shoes.”

Conclusion and implications for modeling

In the near future, Rignot, who is also a senior project scientist at the NASAJet Engine Laboratory (JPL), said this study will provide lasting benefit to the ice sheet modeling community.

“If we put this type of ocean-ice interaction into ice sheet models, I expect we’ll be able to do a much better job of reproducing what’s happened over the last quarter century, leading to a higher level of confidence in our predictions.” “, he said. “If we can add this process that we outlined in the paper, which is not included in most current models, the model reconstructions should match the observations much better.” It would be a big win if we can achieve that.”

Dow added: “We don’t have enough information right now to say one way or the other how long it is before the intrusion of ocean water becomes irreversible. By improving the models and focusing our research on these critical glaciers, we will try to get these numbers to at least be fixed for decades versus centuries. This work will help people adapt to changing ocean levels, along with focusing on reducing carbon emissions to prevent the worst-case scenario.

Reference: “Widespread seawater intrusions beneath the grounded ice of Thwaites Glacier, West Antarctica” by Eric Rignot, Enrico Chiracci, Bernd Scheuhl, Valentin Tolpekin, Michael Wollersheim, and Christine Dow, 20 May 2024. Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2404766121

Rignot, Dow, and Wollershiem were joined on this project by Enrico Ciraci, a UC Irvine assistant professor of Earth system science and a NASA postdoctoral fellow; Bernd Scheuhl, a UC Irvine researcher in Earth system science; and Valentin Tolpekin of ICEYE. ICEYE is headquartered in Finland and operates from five international locations, including the United States. The research received financial support from NASA and the National Science Foundation.