A team led by UC Irvine glaciologists used satellite radar data to reconstruct the effects of warm sea water rising in a several-kilometer-long run-up zone beneath the Thwaites Glacier in West Antarctica. The research that is the subject of a in PNAS, will help climate modelers derive more accurate forecasts of sea level rise caused by the melting of glaciers that limit the ocean around the world. Photo credit: NASA/James Yungel
Satellite radar data show significant intrusion of seawater beneath Antarctica Thwaites Glacierwhich causes ice to rise and fall.
Using high-resolution satellite radar data, a team of glaciologists led by researchers at the University of California, Irvine discovered evidence of warm, high-pressure seawater intruding many kilometers beneath the bed ice of the Thwaites Glacier in West Antarctica. This glacier is often referred to as the “Doomsday Glacier” because of its critical role in possible global sea level rise and the catastrophic impact such a rise would have worldwide. This nickname reflects the glacier’s enormous size and its significant melt rate, which scientists believe could contribute significantly to sea level rise if it collapses or melts completely.
The UC Irvine-led team said widespread contact between seawater and the glacier – a process repeated throughout Antarctica and Greenland – is leading to “severe melting” and potentially a reassessment of global warming forecasts sea level required. Their study was published on May 20th Proceedings of the National Academy of Sciences,
Data and observations
The glaciologists relied on data collected from March to June 2023 by the Finnish commercial satellite mission ICEYE. The ICEYE satellites form a “constellation” in polar orbit around the planet and use InSAR – synthetic aperture interferometer radar – to continuously monitor changes on the Earth’s surface. Many spacecraft flybys over a small, defined area produce smooth data results. In the case of this study, the rise, fall and bend of the Thwaites Glacier were shown.
“These ICEYE data provided a long-term series of daily observations that closely matched tidal cycles,” said lead author Eric Rignot, professor of Earth system science at UC Irvine. “In the past we had some sporadic data available, and with just these few observations it was difficult to figure out what was happening. If we have a continuous time series and compare it to the tidal cycle, we see how the seawater intrudes and recedes at high tide, sometimes traveling further up beneath the glacier and becoming trapped there. Thanks to ICEYE, we can observe these tidal dynamics for the first time.”
Screenshot of a 3D view of the tidal movement of the Thwaites Glacier in West Antarctica recorded by the ICEYE Synthetic Aperture Radar (SAR) constellation based on images captured on May 11, 12 and 13, 2023. Contour planes are ground topography contours at 50 m depth interval. Each interferometric fringe color cycle is a 360 degree phase change, which corresponds to a 1.65 cm shift in the line of sight of the ice surface. The interferogram is overlaid on a Landsat 9 image captured in February 2023. In this study, we show that the limit of tidal bending varies by kilometers over the tidal cycle, suggesting that pressurized seawater can penetrate over kilometers beneath stuck ice and undergo vigorous heat exchange with the glacier base. On the right side of the screen, a separate bull’s-eye pattern shows seawater intrusion extending a further 6 km beyond a protective ridge, suggesting that glacier retreat is still ongoing in this critical part of Antarctica, at a rate of one kilometer per Year. Photo credit: Eric Rignot / UC Irvine
Advanced satellite observations
Michael Wollersheim, co-author, Director of Analytics at ICEYE, said: “Until now, some of the most dynamic processes in nature have not been observed with sufficient detail or frequency to understand and model them. Observing these processes from space and using radar satellite images that enable InSAR measurements with centimeter-level precision at a daily frequency represents a significant advance.”
Rignot said the project helped him and his colleagues develop a better understanding of how seawater behaves at the bottom of the Thwaites Glacier. He said seawater intruding at the base of the ice sheet accumulates along with freshwater generated by geothermal flow and friction and “has to go somewhere.” Water is distributed through natural channels or collects in cavities, creating enough pressure to lift the ice sheet.
“There are places where the water has almost the pressure of the ice above it, so only a little more pressure is needed to lift the ice,” Rignot said. “The water is then compressed so much that it creates a column of ice more than half a mile high.”
And it’s not just any sea water. For decades, Rignot and his colleagues have been gathering evidence about the effects of climate change on ocean currents that push warmer sea water toward the coasts 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 this small difference is enough to contribute to the “severe melting” of the basal ice, the study found.
Implications for sea level rise and future research
Co-author Christine Dow, Professor at the Faculty of Environment University of Waterloo in Ontario, Canada, said: “Thwaites is the most unstable place in Antarctica, experiencing 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 is affecting coastal communities on the would have devastating consequences throughout the world.”
Rignot said he hopes and expects that the results of this project will stimulate further research into conditions beneath Antarctic glaciers, exhibitions involving autonomous robots and more satellite observations.
“The scientific community is very enthusiastic about traveling to these remote polar regions to collect data and improve our understanding of what is happening there, but funding is inadequate,” he said. “We are operating on the same budget in real dollars in 2024 as we were in the 1990s. We need to expand the community of glaciologists and physical oceanographers to address these observational problems sooner rather than later, but for now we are still climbing Mount Everest in tennis shoes.”
Conclusion and implications for modeling
In the near future, Rignot, who is also senior project scientist at NASAThe Jet Propulsion Laboratory (JPL), said this study will provide lasting benefits to the ice sheet modeling community.
“If we incorporate this type of ocean-ice interaction into ice sheet models, I think we will be able to reproduce the events of the last quarter century much better, which will lead to a higher level of confidence in our ice sheet predictions “, he said. “If we could add this process described in the paper, which is not included in most current models, the model reconstructions should agree much better with the observations. It would be a great victory if we could do that.”
Dow added: “Right now we don’t have enough information to say one way or another how much time will pass before seawater intrusion is irreversible.” By improving the models and our research on these critical glaciers focus, we will try to set these numbers at least for decades rather than centuries. This work will help people adapt to changing sea levels while focusing on reducing carbon emissions to prevent the worst-case scenario.”
Reference: “Widespread seawater intrusions beneath the grounded ice of the Thwaites Glacier, West Antarctica” by Eric Rignot, Enrico Ciracì, Bernd Scheuchl, Valentyn Tolpekin, Michael Wollersheim and Christine Dow, May 20, 2024, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2404766121
Rignot, Dow and Wollershiem were joined in this project by Enrico Ciraci, assistant specialist in Earth system science at UC Irvine and a NASA postdoctoral fellow; Bernd Scheuchl, UC Irvine researcher in Earth system science; and Valentyn Tolpekin of ICEYE. ICEYE is headquartered in Finland and operates in five international locations, including the United States. The research received funding from NASA and the National Science Foundation.