5 Jan

Map of the Week: What Does the Land Under Antarctica’s Ice Sheet Look Like?

By Jordan Brennan

A team of glaciologists from the University of California Irvine (UCI) made public the most accurate portrayal of the land underneath Antarctica’s ice sheet yet. In outlining these never before seen contours of the land, the team also shed light on which regions of the continent will be more vulnerable to future climate warming. The new topographical map of Antarctica, BedMachine, and the related findings, were published in the journal Nature Geoscience, and were highly anticipated by the global cryosphere and environmental science communities. BedMachine Antarctica is also available to the public through the National Snow and Ice Data Center in Boulder, Colorado.

BedMachine is a new Antarctic bed topography product that was constructed with ice-thickness data from 19 different research institutes. The data, which dates back to 1967, encompassed nearly one million line-miles of radar soundings. The creators of BedMachine also used ice shelf bathymetry measurements, courtesy of NASA’s Operation IceBridge campaigns, as well as relevant and available seismic information. With the help of BedMachine, researchers were able to zoom into particular regions of Antarctica, enabling the discovery of bumps and hollows beneath the ice that could accelerate, slow down, or even put a temporary stop to the retreat of glaciers. 

Previous methods for mapping Antarctica that relied on radar soundings have been generally effective, though they come with some limitations. Typically, as an aircraft flies in a straight line over certain portions of the continent, wing-mounted radar systems emit signals that penetrate the ice and bounce back from points at which the ice meets solid ground. This data is then used by glaciologists, in conjunction with interpolation techniques, to fill in the areas between the flight tracks. This method however, has proven to be an incomplete approach, especially when fast-flowing glaciers are put into consideration. 

On the other hand, BedMachine relies on mass conservation, a fundamental physics-based method, to estimate what lies between the radar sounding lines. This mass conservation method utilizes satellite data to obtain highly detailed information on ice flow motion and determines how ice moves around the varied contours of the bed. This technique was crucial to their findings regarding the true depth of the Denman trough. Older maps suggested a shallower canyon, however UCI researchers believed that to be impossible, and thought something must be missing. By combining existing radar surveys and ice motion data, they were able to determine how much ice flows through the canyon. According to the calculations, the canyon reaches 3,500 meters below sea level – the deepest point on land. In basing its results on ice surface velocity and ice thickness data from radar soundings, BedMachine is capable of presenting a depiction of the bed topography that is high-resolution and more accurate than others. 

An article published by UCI News reported, “Among the most striking results of the BedMachine project are the discovery of stabilizing ridges that protect the ice flowing across the Transantarctic Mountains; a bed geometry that increases the risk of rapid ice retreat in the Thwaites and Pine Island glaciers sector of West Antarctica; a bed under the Recovery and Support Force glaciers that is hundreds of meters deeper than previously thought, making those ice sheets more susceptible to retreat; and the world’s deepest land canyon below Denman Glacier in East Antarctica.”

According to lead author and UCI associate professor, Mathieu Morlighem, BedMachine will help reduce uncertainty in sea level rise projections from numerical models. He believes that future bed topography mapping on land, which is currently an area of active study, could be greatly improved by charting sea floor depth offshore and beneath floating ice. He also suggests that the study of fast-flowing Antarctic ice sheets would benefit from soundings along flight tracks perpendicular to the flow direction.

Morlighem explained there were many surprises across the continent, especially in regions that hadn’t been mapped in great detail with radar before. Overall, BedMachine presented a mixed picture to researchers. – underlying ground features have kept ice streams in certain areas relatively well-protected, while others on retrograde beds are threatened by potential instability in marine ice sheets.