A team led by glaciologists from UC Irvine used satellite radar data to reconstruct the impact of warm ocean water upwelling in a grounding zone stretching several kilometers beneath the Thwaites Glacier in West Antarctica. Research, the subject of an article published in PNAS, will help climate modelers derive more accurate projections of sea-level rise from melting glaciers around the world that end up in the oceans. Credit: NASA/James Yungel
Satellite radar data show substantial intrusion of seawater beneath Antarctica Thwaites Glaciercausing the ice to rise and fall.
Using data from high-resolution satellite radars, a team of glaciologists led by researchers from the University of California, Irvine has uncovered evidence of warm, high-pressure seawater penetrating many kilometers beneath the grounded ice of the Thwaites Glacier in West Antarctica. This glacier is often referred to as the “doomsday glacier” because of its critical role in potential global sea level rise and the catastrophic consequences such a rise would have worldwide. The nickname reflects the glacier’s enormous size and its significant rate of melting, which scientists believe could contribute substantially to sea level rise if it were to collapse or melt completely.
The UC Irvine-led team said the large-scale contact between ocean water and glaciers — a process replicated throughout Antarctica and Greenland — is causing “vigorous melting” and may require a reassessment of global sea-level rise forecasts. Their study was published on May 20 in Proceedings of the National Academy of Sciences,
Data and observations
Glaciologists relied on data collected from March to June 2023 by Finland’s commercial satellite mission ICEYE. ICEYE satellites form a “constellation” in polar orbit around the planet using InSAR – Synthetic Aperture Interferometer Radar – to continuously monitor changes in the Earth’s surface. Many spacecraft passes over a small defined area provide smooth data results. In the case of this study, it showed the rise, fall and bend of the Thwaites Glacier.
“These ICEYE data provided a long-term series of daily observations that closely match tidal cycles,” said lead author Eric Rignot, professor of Earth systems science at UC Irvine. “In the past, we had sporadic data available, and with just these few observations, it was hard to figure out what was 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 receding and sometimes going deeper under the glacier and getting stuck. Thanks to ICEYE, we are witnessing this tidal dynamic for the first time.”
Screenshot of a 3D view of the tidal movement of Thwaites Glacier, West Antarctica recorded by the ICEYE Synthetic Aperture Radar (SAR) constellation based on images taken on 11, 12 and 13 May 2023. Contours are bottom topography contours at 50 m intervals. Each interferometric fringe color cycle is a 360-degree phase change, equivalent to a 1.65 cm shift in sight distance of the ice surface. The interferogram is overlaid on a Landsat 9 image taken in February 2023. In this study, we show that the tidal flexure limit changes by kilometers during the tidal cycle, suggesting that pressurized seawater is able to penetrate beneath the grounded ice for kilometers and strongly settle down heat exchange with the glacier base. On the right-hand side of the screen, a separate bull’s-eye pattern shows seawater intrusion spreading another 6 km beyond the 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 Analytics Michael Wollersheim, a co-author, said: “Until now, it has not been possible to observe some of the most dynamic processes in nature in sufficient detail or frequency to understand and model them. Observing these processes from space and using radar satellite imagery, which provides centimeter-accurate InSAR measurements at a daily frequency, represents a significant leap forward.”
Rignot said the project helped him and his colleagues better understand the behavior of seawater on the underside of the Thwaites Glacier. He said seawater arriving at the base of the ice sheet, combined with freshwater generated by geothermal flow and friction, accumulates and “has to flow somewhere.” Water is distributed through natural conduits or collected 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,” Rignot said. “The water is then squeezed out enough to pick up a column of more than half a mile of ice.”
And it’s not just any seawater. Rignot and his colleagues have been gathering evidence for decades about 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 basal ice, the study found.
Impact on 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 and includes 60 centimeters of sea level rise. We worry that we are underestimating the rate at which the glacier is changing, which would be devastating to coastal communities around the world.
Rignot said he hopes and expects the results of this project to spur further research into conditions beneath Antarctic glaciers, exhibits involving autonomous robots and other satellite observations.
“The scientific community is very excited to go into these remote polar regions to collect data and build our understanding of what’s going on, but funding is lagging,” he said. “We’re working with the same budget in 2024 in real dollars as we were in the 1990s. We need to expand the community of glaciologists and physical oceanographers to solve these observational problems sooner rather than later, but right now we’re still climbing Mount Everest in sneakers.”
Conclusion and implications for modeling
In the near future, Rignot, who is also a senior project scientist at the company NASAJet Propulsion Laboratory (JPL), stated that this study will provide a 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 projections,” he said. “If we could add this process, which we outline in the paper and which is not included in most current models, the model reconstructions should match the observations much better. It would be a great victory if we could achieve that.”
Dow added: “We don’t have enough information at this point to say one way or the other how much time is left before ocean water intrusion becomes irreversible. By improving the models and focusing our research on these critical glaciers, we will try to at least fix these numbers to decades versus centuries. This work will help people adapt to changing ocean levels, while focusing on reducing carbon emissions to avoid the worst-case scenario.”
Reference: “Widespread seawater intrusions beneath the grounded ice of Thwaites Glacier, West Antarctica” by Eric Rignot, Enrico Ciracì, Bernd Scheuchl, Valentyn 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 the project by Enrico Ciraci, a UC Irvine assistant specialist in Earth systems science and a NASA postdoctoral fellow; Bernd Scheuchl, a UC Irvine researcher in Earth system sciences; and Valentyn Tolpekin of ICEYE. ICEYE is headquartered in Finland and operates in five international locations, including the United States of America. The research received financial support from NASA and the National Science Foundation.