Using radar surveys, researchers took a look beneath the East Antarctic ice sheet and thus into the continent's past. Accordingly, the landscape in an area near the east coast of Antarctica was formed by large rivers more than 14 million years ago, probably even 34 million years ago - before Antarctica completely iced over. The mountains and valleys have been preserved under the ice sheet to this day. Since only minor changes caused by later ice movements can be seen, the researchers assume that the ice cover formed quickly and has been untouched for at least 14 million years. Given climate change, it could melt in the future and reveal the underlying landscape for the first time.
At the transition from the Eocene to the Oligocene around 34 million years ago, the first glaciers formed in Antarctica. Since the temperatures were significantly higher than today, the extent of the ice changed again and again over the following millions of years until, around 14 million years ago, the atmosphere cooled enough to form a stable ice sheet that still covers the continent today. Sediment studies indicate that the ice sheet retreated further inland during warm phases, but to what extent this occurred is still unclear.
Evidence of past and future changes
A team led by Stewart Jamieson from Durham University in Great Britain has now analyzed the landscape beneath the East Antarctic ice sheet using radar surveys and the shape and movement of the ice surface. “The land beneath the East Antarctic ice sheet is less well-known than the surface of Mars,” says Jamieson. "And that's a problem because this landscape affects the way the ice in Antarctica flows and how it might respond to past, present and future climate changes."
The research team focused on an approximately 32,000 square kilometer land area in the Aurora Schmidt subglacial basin in eastern Antarctica, near the coastal Denman and Totten glaciers. “This area of the East Antarctic ice sheet is considered vulnerable to climate change and ocean warming, both in the past and potentially in the future,” explain Jamieson and his team. “We examined this part of the landscape in more detail to find out what it can tell us about the evolution of the landscape and the ice sheet.”
Ancient landscape under the ice
The radar surveys revealed beneath the ice a landscape of three highland blocks separated by deep valleys. “This landscape was not eroded by the ice sheet and was apparently created by rivers before the ice appeared,” Jamieson says. “We believe that this land surface is at least 14 million years old. It may even date back to the transition from warm to glacial conditions 34 million years ago.”
Because the surface of the landscape formed by rivers is still preserved beneath the ice, the researchers conclude that the transition to full ice cover occurred quickly and that the ice sheet in this region has been stable since then. “The state of preservation of the landscape makes it unlikely that the ice boundary retreated inland to this location during the warm periods of the last 14 million,” writes the team of authors. “The landscape is more consistent with the idea that this region of East Antarctica requires more warming for the ice retreat to reach that far.”
Ice sheet retreat?
These results are also important for forecasting possible changes in the face of climate change. “As modern CO2 and temperature conditions have reached levels unprecedented since the Pliocene, with continued burning of fossil fuels we are on track to develop atmospheric conditions similar to those between 34 and 14 million years ago, when it occurred “It was about three to seven degrees warmer than today,” the researchers write. “According to our work, this anthropogenic influence and the associated global warming could cause the East Antarctic ice sheet to retreat to such an extent that the landscapes on the edge of the Aurora Schmidt Basin would only be covered by local ice caps.”
Source: Stewart Jamieson (Durham University, UK) et al., Nature Communications, doi: 10.1038/s41467-023-42152-2