Scientists have detected an ancient river landscape that dates back millions of years and is now buried under more than a mile of ice in Antarctica, reports a new study.
The discovery offers a rare glimpse of a long-lost Antarctic world shaped by rivers and plants, while also helping scientists predict how this critical continent might respond to human-driven climate change in the future.
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Antarctica is almost entirely covered by ice sheets, making it by far the most frigid and otherworldly landmass on Earth. But tens of millions of years ago, dinosaurs and other animals roamed this far-flung continent when it was part of a much warmer patch of the supercontinent Gondwana. Even after the breakup of Gondwana, Antarctica hosted lush vegetation and tundra ecosystems until it finally became mostly glaciated within the past 20 million years. While some hardy lifeforms still exist here, including the iconic Emperor penguin, the continent’s hospitable heyday is long over.
Now, scientists led by Stewart Jamieson, a glaciologist at Durham University in the United Kingdom, have used satellite observations to peer under two kilometers (1.25 miles) of a region called the East Antarctic Ice Sheet (EAIS). With this approach, the team detected “an extensive relic pre-glacial landscape preserved beneath the central EAIS despite millions of years of ice cover” which hints there are “other similar, as yet undiscovered, ancient landscapes beneath the EAIS,” according to a study published on Tuesday in Nature Communications.
“We’ve had a longtime interest in, effectively, the shape of the land beneath the ice sheet in Antarctica, and in particular, how the shape of that landscape interacts with the ice itself in terms of controlling it, but also in terms of recording how it has behaved in the past, so that it leaves a signature, or a fingerprint,” Jamieson said in a call with Motherboard.
“What we’re trying to do is identify where we can really see an obvious picture in the land beneath the ice, and map it out,” he continued. “The East Antarctic Ice Sheet has existed for 34 million years. It’s a very long-lived chunk of ice and we want to use the landscape to try and understand if we actually can see anything about the stability of the ice sheet.”
In order to probe this buried landscape, Jamieson and his colleagues had to figure out how to gaze through this extremely thick and ancient slab of ice. Aerial and ground expeditions to the EAIS can provide some insight into subglacial landscapes in these areas, but this approach is expensive and only covers relatively small areas.
To get a broader view, the researchers turned to data collected by the Canadian satellite constellation RADARSAT. These spacecraft can detect tiny anomalies in the surface of the ice that hint at the topography below. For example, mountains that are buried under the sheet can produce very subtle bumps on the ice that might not be detectable from the ground or the air, but that can be seen from space.
Jamieson used this technique to fill in some of the missing gaps of survey observations taken in recent decades. The results revealed the remains of a bygone landscape roughly the size of Wales, which was sculpted by rivers that once flowed in the deep past. The researchers think that this ancient world might date back more than 34 million years old, making it older than the EAIS.
“The implication is that this must be a very old landscape that was carved by rivers before the ice sheet itself grew,” Jamieson explained. “That’s why we can say that the landscape itself is likely older than 34 million years. That’s a time when the climate was a bit warmer. There was vegetation and plants growing on Antarctica and there wasn’t big-scale ice.”
“Although in a lot of areas, landscapes like this would be scrubbed away by glacial erosion that’s happening underneath the ice sheet, in this particular location, glacial erosion doesn’t seem to be switched on,” he added. “That’s effectively because there is no water layer, lubricating the interface between the ice and the bed, so it’s not sliding. It’s not filing off the landscape. It’s just frozen sitting there, like a protective cap. Because we can still see a river imprint, we think it must have basically been doing that for pretty much all of ice sheet history in Antarctica.”
It’s tantalizing to imagine this ancient terrain, once resplendent with life, that is now entombed in intricate detail under the ice sheet. In the future, it may even be possible to drill down through the EAIS to procure a sample of the landscape, which could help to confirm its ancient age.
In the meantime, though, Jamieson and his colleagues hope to extract more details about the terrain using remote-sensing methods so that they can reconstruct the evolution of the ice sheet over time. Because the EAIS is “known to be sensitive to past and potentially future climate and ocean warming,” this information could, in turn, help scientists understand how this massive sheet might respond to human-driven climate change, according to the study.
“A deglaciation of this area is not going to happen anytime soon,” Jamieson said, noting that the landscape they studied is more than 200 miles inland from the ice sheet edge. “But the key point is that between the coast where the ice margin sits now, and our landscape, is the zone in which we would expect that maybe there will be some possibility for the ice margin to retreat in the future. That’s where computer modeling and simulations of the future are going to help us really investigate this in more detail.”
“What is going to happen around the fringes of the ice sheet in the relatively near future—the future that’s going to impact us and our grandchildren and the next several generations? That initial retreat, how fast and how much that can happen, that’s going to be the important thing for us,” he concluded. “We want to be in a situation where that retreat isn’t happening. It’s still a possibility that we can avoid that retreat, but it does involve some pretty rapid action on emissions.”
