The audacious engineering ideas to save Antarctic ice

How are Cambridge’s engineers helping to tackle some of the biggest questions facing Antarctica? From seabed curtains to slowing glaciers, to thickening sea ice - these are bold, radical, and sometimes controversial ideas that just might make a difference. I’ve been speaking with Shaun Fitzgerald and Hugh Hunt from Cambridge University's Department of Engineering. I began by asking Hugh about an audacious sounding idea to channel glacier meltwater away from problem areas on the seafloor...

Hugh - The glaciers are sliding on the bedrock, and in the same way as your car tyres might slide on a wet road, you might want to have more grip at the bottom of the glaciers on the bedrock. Now, having meltwater at that interface between the glaciers and the bedrock is making it easier for the glaciers to slip. Can we pump out that meltwater? Or perhaps even can we create channels for that meltwater to go through, a bit like putting tread on your tyres to increase the grip?

Chris - The concept being then that rising temperatures mean more meltwater. The meltwater finds its way under the glacier, and then it's the lubricant between the ice and the bedrock. But this is huge, isn't it? Are we not talking absolutely massive scales here? Is it realistic to think that we could carve a tunnel under a glacier to take that water away?

Hugh - If we target the really bad places and find particular points in that glacier where grounding them in some way would make a difference, and it's really about trying to manage expectations. We can't do every single glacier everywhere, but we can perhaps do a few important ones.

Chris - Have we got the technology to do the engineering, though? Presumably we have. If we can build big tunnels under the ocean, presumably we can melt holes under ice.

Hugh - I think we have to assume that we can until such time as we prove that we can't.

Chris - Shaun, let's come over to you and go topside for a minute, because one of the things you're advocating for is the fact that if we're losing ice during the summer when temperatures are high, can we make up for that in wintertime and therefore start with more to start with? Therefore we've got more to lose, as it were. How do you propose to do that?

Shaun - One of the ideas is by after the sea ice has, say, formed and you've got 50 centimetres of thickness, how about then pumping seawater on top of the sea ice? The reason is that the sea ice is a pretty good insulator, and therefore as the sea ice forms naturally, what happens is that any new sea ice that forms on the underside of it, well, the latent heat of solidification has to be conducted up to the very cold Arctic air and then radiated out to space through an ever thickening layer of insulating sea ice. So if you bypass that insulating effect and just pump seawater on top, then the freezing process will then occur in direct contact with the very cold Arctic air and be able to radiate out to space. This is the question that we are asking as to whether that is possible. Does the sea ice that forms, which would then possibly be thicker by the end of the winter, does it actually last longer? Because we have then brought brine, seawater, including the salt, up to the surface and we've got to be sure that we haven't just made the sea ice thicker, but it actually does last longer over the course of the summer.

Chris - What's the energetic argument? If you actually do the calculations, how much energy have you got to expend to pump that water to then make that ice? And how feasible is that when you look at the amount of energy involved? Because this is going to be presumably diesel or electric pumps. Ultimately, there's going to be a big footprint of energy that's going to be expended to get that ice back.

Shaun - So there's a twist, Chris. One of the ideas is if you think sea ice is a good insulator, well, any snow that falls on the sea ice is an even better insulator. So the twist is this. If you just pump seawater on top of the sea ice, but just enough to flood any snow that is there and then allow that to freeze, you've converted what was a super insulating material, namely snow, into a less insulating material, namely ice, and that will then allow sea ice to form naturally on the underside of the sea ice more quickly. And the initial estimates are that the amount of energy that you need to expend for a given amount of ice thickness accumulation is lower. So that's a more energy efficient way of doing this. And we're looking at both approaches in this research.

Chris - Back to you, Hugh, and back underwater, I've never heard of a subsea curtain to stop a glacier falling apart. Tell us more.

Hugh - These glaciers are more and more vulnerable to warm water. You might think that warm water is less dense, so it'll float up to the surface of the oceans, but warm, salty water can be pretty dense and it gets down to the bottom of the oceans and fresh, cold water, which is coming off the glaciers, rises up to the surface. And there's this circulation that, as it were, sucks the warm water to the toes of the glaciers. Now, imagine if you could put some kind of barrier, a dam of some sort, to hold that warm water back. Well, you might not want to build concrete dams and things, but you might want to hang, as it were, upside down some curtains, some fabric curtains. So you would anchor this curtain on the seafloor and it would be held up maybe a quarter of the way up towards the surface of the ocean, deflecting the warm water away, getting it to mix with the cooler water and that way protecting the glaciers from the warm water melting.

Chris - But you've got very cold, fresh water melting off the bottom of the glacier. You told us about that earlier, about the importance of trying to deflect that into channels so we un-lubricate the glaciers. That would normally hit the seafloor and mix with this more dense brine that's there, that's warmer. Is there not a threat that you're therefore going to get this very cold fresh water hitting the seafloor, becoming concentrated on the seafloor? There's lots of life down there, sea spiders that Lloyd Peck at the BAS is very keen on telling us about, he loves those. Is this not going to be environmentally disastrous because we will upset that natural circulation?

Hugh - It is very important to make sure that whatever interventions we even start to think about, let alone do, are respectful of the unintended consequences. The places where this kind of intervention would be useful is where that flow that you've been talking about, the cold water moving away from the glaciers along the seafloor, where that flow has been reversed and where what is happening is that it happens at that location that the warm, salty water is more dense than the cold, fresh water. So the circulation, which normally goes down the face of the glacier and away from the glacier, where that has been disturbed and reversed. And so that is where you need to intervene and try to disturb, deflect the warm, salty water.

Chris - This sounds also a bit like a material science problem because those curtains are presumably going to have to be pretty tough and pretty extensive to take the environment, but also take what will be quite a big force down on them by this very heavy, dense water that's trying to displace downwards.

Hugh - So the engineering aspects of designing seabed curtains is huge. The big forces involved. It's a little bit like when you go to the supermarket and you see maybe a forklift truck going into through a plastic curtain wall that goes into the warehouse, which is refrigerated. Well, you can imagine that upside down where these curtains might not be a fixed curtain, but might be made up of slats, which means that ships and icebergs and for that matter, fish and other things can get through the curtains.