What if the fate of future coastlines is controlled by rivers that vanished a hundred million years ago? Hiding under the East Antarctic Ice Sheet, a system of river-carved plains buried beneath more than two kilometers of ice is a missing puzzle piece in the mystery of ice-sheet behavior and sea-level rise.
New work by Dr. Guy Paxman and others at Durham University, published in Nature Geoscience, mapped a 3,500-kilometer wide belt of these flat areas from Princess Elizabeth Land to George V Land using airborne radio-echo sounding (RES). Scientists combined data from four main surveys WISE-ISODYN, ICECAP, CHINARE, and NASA’s Operation IceBridge with vertical resolutions of 5–10 meters and along-track sampling densities of about 20 meters. This technological advance enabled researchers to identify low-relief, gently coastward-dipping surfaces that have lasted more than 30 million years of glaciation.
Dr. Paxman described the subglacial landscape as “one of the most mysterious not just on Earth, but on any terrestrial planet in the solar system,” pointing to the unexpected preservation of the plains. “The flat surfaces we have found have managed to survive relatively intact for over 30 million years, indicating that parts of the ice sheet have preserved rather than eroded the landscape,” he told Phys.org.
Their origins go back to an age after the break-up of Australia and East Antarctica, around 80 million years ago, but prior to the continent being covered in ice some 34 million years ago. By this time, large river systems had cut out a extensive coastal plain, which is now hundreds of meters below sea level after isostatic adjustment. As advancing ice sheets moved outward, they tended to flow preferentially along existing valleys and tectonic weaknesses, scooping out deep troughs, leaving the higher and broader areas intact.
The implications for ice dynamics are extensive. These intact plains are mechanical brakes on swift ice flow, entrapping glaciers in deep troughs and slowing the overlying ice. As Professor Neil Ross of Newcastle University said, “This study brings the jigsaw pieces of data together, to reveal the big picture: how these ancient surfaces formed, their role in determining the present-day flow of the ice, and their possible influence on how the East Antarctic Ice Sheet will evolve in a warming world.”
It is now a priority to incorporate these features in future ice-sheet models. Current-day most models lack the spatial resolution to see the stabilizing impact of these subglacial plains, which could lead to huge underestimation of ice-sheet resilience during times of warming. Cold-based, slow-moving ice over these plains must have been confined, while swift-flowing glaciers such as Totten and Denman are locked up in the deep troughs. This geometry could potentially stabilize ice in future retreat events and form “ice rises” that buttress the inland ice and slow down grounding-line migration.
It is especially significant to comprehend such processes since East Antarctica holds enough ice to raise the world’s sea level by 52 meters in the event of its melting. Even small changes in the rates of ice flow can potentially generate disproportionate outcomes for coastal societies worldwide. The integration of high-resolution subglacial topography into predictive models, and suggested subglacial drilling and rock sampling programs, will provide us with key constraints on the timing and duration of these landscapes and indicators of ancient warm periods and future sensitivity.
Radio-echo sounding remains the cornerstone of Antarctic subglacial research, but its synergy with seismic tomography, satellite gravimetry, and direct drilling is set to revolutionize the field. As Dr. Tom Jordan of the British Antarctic Survey noted, “Understanding the ancient landscapes that influence present-day ice flow is crucial if we’re to predict how this huge ice sheet will behave in the future”.
Just as with each new line of survey and core sample, the interplay of geology, hydrology, and ice dynamics becomes more apparent. For young modelers and scientists, the challenge now is to integrate these hidden landscapes into the next generation of ice-sheet and sea-level projections, closing the gap between the secrets that lie hidden beneath the ice and the future of a warming planet.
