I remember learning about the existence of lakes under the Antarctic ice sheet a while back. It was something that just hadn’t occurred to me as a possibility, but if they’re there, they’re there, and that’s pretty neat. I think part of my brain insists on forgetting that while Greenland is big, Antarctica is quite a bit bigger. It makes sense that the diversity of sub-ice conditions on a continent would lead to liquid water in some places. I thought, “Cool! I bet there’s interesting microbial life down there”, and didn’t really give it much thought after that.

But, now that I think of it, if there are conditions for liquid water under billions of tons of ice, then it makes sense that those melt points wouldn’t necessarily be where water would pool into lakes. If there are sub-ice lakes, then there must also be water flowing under there, right? Still, there hasn’t been actual evidence for them, beyond the discovery of lakes. Now, a team of researchers has discovered a large river system under the ice.

The 460km-long river is revealed in a new study, which details how it collects water at the base of the Antarctic ice sheet from an area the size of Germany and France combined. Its discovery shows the base of the ice sheet has more active water flow than previously thought, which could make it more susceptible to changes in climate.

The discovery was made by researchers at Imperial College London, the University of Waterloo, Canada, Universiti Malaysia Terengganu, and Newcastle University, with the details published today in Nature Geoscience.

Co-author Professor Martin Siegert, from the Grantham Institute at Imperial College London, said: “When we first discovered lakes beneath the Antarctic ice a couple of decades ago, we thought they were isolated from each other. Now we are starting to understand there are whole systems down there, interconnected by vast river networks, just as they might be if there weren’t thousands of metres of ice on top of them.

“The region where this study is based holds enough ice to raise the sea level globally by 4.3m. How much of this ice melts, and how quickly, is linked to how slippery the base of the ice is. The newly discovered river system could strongly influence this process.”

Currently, Antarctica doesn’t have the same kind of surface melting seen in Greenland, where summer meltwater flows down through cracks and holes in the ice, and then flows along the ground underneath it. I guess there’s also been no clear sign of rivers emptying into the seas around the continent before now, so it has been impossible to calculate what effect, if any, sub-surface water could have on ice melt and sea level rise. It seems pretty unequivocal – these rivers are not caused by global warming. They’ve always been there, we just haven’t been able to detect them. What scientists need to figure out is how these rivers are or are not represented in past calculations about ice movement, and what role they will play as the temperature continues to rise.

That such a large system could be undiscovered until now is testament to how much we still need to learn about the continent, says lead researcher Dr Christine Dow from the University of Waterloo.

She said: “From satellite measurements we know which regions of Antarctica are losing ice, and how much, but we don’t necessarily know why. This discovery could be a missing link in our models. We could be hugely underestimating how quickly the system will melt by not accounting for the influence of these river systems.

“Only by knowing why ice is being lost can we make models and predictions of how the ice will react in the future under further global heating, and how much this could raise global sea levels.”

For example, the newly discovered river emerges into the sea beneath a floating ice shelf – where a glacier extending out from the land is buoyant enough to begin floating on the ocean water. The freshwater from the river however churns up warmer water towards the bottom of the ice shelf, melting it from below.

Co-author Dr Neil Ross, from the University of Newcastle, said: “Previous studies have looked at the interaction between the edges of ice sheets and ocean water to determine what melting looks like. However, the discovery of a river that reaches hundreds of kilometres inland driving some of these processes shows that we cannot understand the ice melt fully without considering the whole system: ice sheet, ocean, and freshwater.”

If Antarctic surface melting starts catching up to Greenland, that would cause the existing river systems to “flood”, just like a big storm does on warmer continents, but it’d be more constant. Presumably that would speed up the movement of ice, which would itself increase heat generated from friction, which would melt more ice, and so on. This isn’t the kind of thing that’s going to happen overnight, but it could be a process that, once started, would be difficult or even impossible to stop. As with so much else in the climate crisis, momentum matters.

I do want to end on a more speculative note, however. Since we now know that these rivers do connect with the oceans, are there fish that use them? Anadromous fish exist in every other continent, so far as I’m aware, but I don’t know if there’s enough food in these rivers’ microbial ecosystem for the babies to feed themselves. On the other hand, there would be no danger of aerial or terrestrial predators. I know we’ve already solved the eel mystery, but are there any other fish that seem to just sort of disappear for part of the year?

I’m not going to lie – I’m very much hoping they discover ecosystems based on sub-ice volcanic activity, similar to deep-water hydrothermal vents. There could be all sorts of critters just living out their lives in complete darkness under there!

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