Observations from ESA’s CryoSat mission have helped scientists to investigate the long-term evolution of the Thwaites Glacier ice shelf in West Antarctica, delivering new insight into the complex mechanisms that are contributing to its continued retreat. 

The Thwaites Glacier is a vast expanse of flowing ice spanning more than 150,000 square kilometres and experts have warned that its partial or total collapse could trigger a significant rise in sea levels.

Part of what keeps the glacier in place is an ice shelf that juts out into the ocean, acting as a barrier that holds the glacier back and tempers sea level rises caused by melting glacial ice.  

In recent decades researchers have established that this critical ice shelf is highly vulnerable to warming global sea temperatures, with the greatest melt rates observed at the point where the ice shelf meets the ocean floor, known as the grounding line. 

As part of the study – published in the EGUspheres scientific repository – researchers from US institutes used a digital surface model, named the Reference Elevation Model of Antarctica (REMA), to observe the retreat of the grounding line and identify channels of flowing melt water under the ice. This analysis covered from 2010 to 2022. 

REMA is composed of data from high resolution optical satellites, but ice elevation data from CryoSat’s interferometric radar altimeter play a crucial role in ensuring its accuracy. 

Allison Chartrand, scientist at the University of Maryland and lead author of the study, explains, “One of the main challenges in working with the REMA digital surface model is that it must be compared, or ‘registered’, with control points from other data sources to remove biases in its outputs. 

“CryoSat is the only mission that has continuous coverage of surface elevations in Antarctica over the same time period as REMA, so it is the go-to dataset for this application.”

The team used CryoSat observations collected between 2011 and 2018, to register REMA digital surface models covering the same timescale. Elevation data collected by NASA’s ICESat-2 mission were used to register models covering later periods. 

CryoSat elevation data enabled the researchers to improve the vertical accuracy of the REMA digital surface models from 4 metres to less than 1 metre, allowing a more detailed investigation of ice shelf and the channels of melt water beneath it. 

The team found that the areas of the ice shelf that experienced the highest rates of grounding line retreat (up to 0.7 kilometres per year) also displayed the highest rates of ice thickness losses (up to 250 metres per year). This mainly occurred where channels carrying melt water meet the grounding line and where the land beneath the ice exhibits a retrograde slope.

Benjamin Smith, scientist at the University of Washington and contributor to the study, added, “This analysis was made possible thanks to the complementary attributes of CryoSat and REMA, with CryoSat providing continuous surface elevation data and REMA providing high resolution optical data on the ice shelf’s channels, rifts and crevasses.

“By combining these strengths, we can measure precise changes at very small scales.”
In the future, the team plan to use the method developed in the current study to further investigate areas in which both grounding line retreat and sub-surface channels are observed. It is hoped that elucidating these complex interactions will enable more accurate estimates of current and future changes to the Thwaites Glacier ice shelf. 

The Thwaites Glacier study was completed as part of a collaboration between the following research institutes: the Earth Science Systems Interdisciplinary Center, University of Maryland; the NASA Goddard Space Flight Center Cryosphere Lab; the Byrd Polar and Climate Research Center, Ohio State University; the Polar Science Center, Applied Physics Laboratory, University of Washington.