Science Friday - Deep-Sea ‘Nodules’ May Produce Oxygen | A Bird’s Physics Trick For High-Altitude Flying

Episode Date: August 7, 2024

New research suggests that polymetallic nodules found 13,000 feet deep produce “dark oxygen” by electrolyzing water. Also, at higher altitudes, the air is less dense, which makes it harder for birds in flight to generate lift. The turkey vulture has a solution. Deep-Sea ‘Nodules’ May Produce Oxygen, Study FindsAn international team of researchers recently discovered that some 13,000 feet below the ocean’s surface, oxygen may be produced through natural electrolysis. The group found that small lumps called polymetallic nodules at the bottom of the ocean appeared to act as geo batteries, producing enough electricity to break down water and make oxygen.That observation challenges the idea that photosynthesis is necessary to produce enough oxygen for living organisms. The researchers hypothesize that this could be a source of oxygen for deep-sea creatures. But while it gives some answers as to how life can thrive at the bottom of the sea, it also raises a lot of new questions.Science Friday guest host and producer Charles Bergquist is joined by the lead electrochemist of the study, Dr. Franz Geiger, the Charles E. and Emma H. Morrison Professor of Chemistry at Northwestern University, to answer some of these questions.One Bird’s Physics Trick For Flying At High AltitudesIf you’ve ever taken a trip to a higher elevation, you know that the air gets thinner as you go up. If you’re not acclimated to the altitude, it can feel harder to breathe. That thinner air also makes it more difficult for birds and airplanes to fly, because it’s harder to produce the lift forces in thinner air. But it turns out that turkey vultures have a way of dealing with that problem.Researchers observed turkey vultures in flight at different altitudes and found that rather than flapping harder or more rapidly to deal with decreased lift, the turkey vulture exploits the lower drag in thinner air to fly faster, using increased speed to help balance the lift equation. Dr. Jonathan Rader, a postdoctoral research associate in biology at the University of North Carolina Chapel Hill and an author of a report on this research published in the Journal of Experimental Biology, joins SciFri’s Charles Bergquist to explain how flying things work to adapt to different flight conditions.Transcripts for each segment will be available after the show airs on sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

On the cold, dark ocean floor, layered metallic lumps might be producing oxygen without photosynthetic life. The team decided this can't be right, and they didn't believe they were data for a long time. It's Wednesday, August 7th, and you're listening to Science Friday. I'm SciFRI producer Kathleen Davis. Coming up, how potato-sized objects called polymetallic nodules, millions of years old, might be an unseen source of oxygen. for the deep ocean, and what that might mean for the search for life elsewhere in the universe. But first, how a trick of physics lets Turkey vulture soar sky high, as high as some airplanes. Here's guest host Charles Berkwist.

If you've ever taken a trip to a higher altitude, you know that the air is thinner up there. And if you're not used to it, you might want to take it easy. Maybe don't plan to go running the first day you arrive in the mountains. that thinner air also makes it more difficult to fly. But it turns out that a bird, the turkey vulture, has a way of dealing with that problem. Here to explain is Dr. Jonathan Rader, a postdoctoral research associate in biology at the University of North Carolina Chapel Hill, and an author of a report on this research published in the Journal of Experimental Biology. Welcome to Science Friday, Dr. Rader.

Hi, Charles. Thank you. It's lovely to be here with you today. Thanks for being here. So for listeners who may not be totally up on their birds, what is a turkey vulture? These are not small birds. No, they're a large bird, I don't know, about a foot and a half tall when they're sitting on the ground, and they've got a wingspan of around six feet. Wow. And they weigh somewhere between three and four pounds, about the size of a small dog. You know, most people have probably seen a turkey vulture.

They're common across all of the Americas. They're all over North America, Central, South America. And as you're driving down the road, they're going to be the large blackbird that's just kind of hanging out, cruising around in the air somewhere above the highway. When I see those vultures circling over the highway, what are they doing? Are they just looking for roadkill? Yeah, when they're circling like that, they probably found a thermal, which is a highly localized rising updraft of warm air.

And this is one of the ways the vultures can take advantage of energy from the environment. They put themselves into one of those thermals, the air is rising, and they just hang out and rise with the air. It's a really energetically inexpensive way to gain some altitude, and then they can glide around and look for roadkill or carrying lane on the landscape. They live in places then with very different elevations. How big a range of elevation do they need to deal with? What's the span here? Well, so like I said, they live all across the Americas, which means that they live at the coast.

They live at the highest mountains in the Rockies, the Andes. So we're talking about, you know, up to 15,000 feet of elevation change just on the land. And then they also have been observed flying at ridiculous heights. So airline pilots have reported seeing them as high as 11, 12,000 feet in the air. There are some reports of seeing them higher, but unsure about those. Wow. You know, we recently visited Colorado, and I felt that the air was thinner. But how much thinner is it at 11,000 feet up or wherever these turkey.

Fulchers are flying. Oh, it's at 11,000 feet, it's almost 40% thinner. Wow. So if you need to be able to fly in all of these different conditions, what does that do to your flight capabilities? Is it 40% harder to fly at 40% less air? Yeah, so the decrease in lift is kind of linear. You take any individual flying thing. There are three main things that go into how much lift it can produce. It's the size of their wings, the density of the air, and how fast they're flying. And there's some other things that go into it, but those are mostly comparisons among different kinds of flyers. And so if you've got a 40% reduction in air density, yeah, that means that you're making 40% less lift. And so you have to do something about it.

So how does the Turkey Vulture then stay aloft even in these low lift conditions? Well, that was the point of our study. We got interested in this when I was starting my PhD work, also at UNC Chapel Hill with Ty Hedric. and some other work has been done showing that individual birds fly faster as they climb up in altitude. And we were interested in whether or not that same kind of pattern happens across different populations of birds that live at different elevations. So we started at home in Chapel Hill, which is about 80 meters of elevation, 400-ish feet, and recorded a bunch of birds flying there. And then we went up to high elevation in Wyoming and recorded the birds there. and what we found is that the birds in Wyoming at high elevation fly faster.

Is that linear too? I mean, do you have to fly 40% faster to make up for the 40% less lift? No, this one actually kind of works out better in the vulture's favor. If you look at the lift equation, the amount of lift that you get out of an increase in speed is actually speed square. So they don't have to increase linearly. A smaller amount of increased speed will give them the appropriate amount of extra lift. So this faster flight, does this come at a big metabolic cost for the birds?

Do they have to consume more when they're in higher elevations to deal with increased energy expenditure or something? That's the lovely thing about vultures. They're kind of lazy. And so this increase in airspeed is a way of getting around having to do something energetically expensive, like flapping more or flapping harder. By just increasing their air speed, they're able to. get around this lift problem without expending a lot of energy. That's great because there's vultures eat carry-on, which means there's not a lot of foraging available on the landscape. So, wait, how do you get a higher air speed without flapping faster or harder? It turns out that the drag forces that are restraining vulture flight also decrease with air

density and by about the same amount. So they don't have to do anything to go faster that just they are going faster at these higher elevations. Yeah, that's kind of how it works out. I mean, it didn't have to be that way. We could have gone up to the high elevation, or we could have found similar adaptation of higher elevation birds having larger wings or something like that. But we didn't find any evidence of that,

and we didn't find any evidence that they're flapping more or flapping harder at high elevation. So you mentioned other adaptations that birds have for this flight problem. Do you need bigger wings or different feathers or something? something than low elevation birds? Yeah, exactly. Some other studies have found that high elevation birds have proportionally larger wings when you compare them to low elevation birds.

And then in some species of hummingbirds, particularly, when they're flying at high elevation, they're just flapping harder. They're putting out more muscular power in order to move enough air to keep themselves aloft. When we talk about birds needing bigger wings for dealing with different elevations, is that just a species level thing? Like, you know, robins have smaller wings than vultures? Or do you find that vultures living in Wyoming have larger wings than vultures living in North Carolina? Well, it happens across species.

So high elevation birds in general, and this has mostly been started. studied in songbirds. There's no evidence that there's, there are differences in wing size among among vultures, at least not turkey vultures. So vulture is a vulture. You don't have highland vultures and lowland vultures. Kind of, yeah. Yeah, but it's a great question because, and it has, exactly what you're asking, it has been found in songbirds. High-eolation birds have bigger wings, low-elevation birds have comparatively small wings. And then there are a couple of species that have been studied in detail across elevations, and the ones that live in the ones that live in at higher elevation do seem to have bigger wings.

Interesting. On a human level, do airplanes also need to speed up when they're up higher? Do human engineers use a different way to get around this problem? No, the same airplane will increase its cruising speed at higher altitudes than when they're flying at lower altitude. Staying with aircraft, I know that heat can lead to a similar sort of thin air problem. Do birds have to fly faster when it's hotter out? Yes.

So in our study, we had to correct for a thing that's called density altitude. And so there are a number of things that go into affecting air density. One of them is, of course, the elevation question that we were directly after. But also humidity reduces air density, even though on a humid day that feels like you're walking through P-Soup. The air density is actually lower when it's really humid. And then heat also reduces the air density. What about winds up there?

I mean, it can get pretty windy at high elevations. Yeah, and in fact, many of the days that we spent recording in Wyoming were quite windy. In fact, the wind speeds sometimes approached the flight speeds of the birds. And so we were interested in how the birds deal with that. And it turns out that in that case, they also increase their airspeed enough that they can still make some forward progress into the strong headwind. So where do you go with this next? What's the next question that you want to answer about this problem? problem. So I'm really, I've become really interested in just how lazy vultures can be. Like I said,

they live a life that is sort of resource poor. And that means that they have to be absolute masters at extracting as much energy from the world around as they can, which means that I suspect that they're exquisitely adapted to taking advantage of small air currents. We know that they take advantage of rising thermals in order to gain altitude. So I think that a really interesting thing to do would be to track a bunch of different vultures flying around the landscape and try to build sort of an energy budget for the birds for each day that they're out foraging. Dr. Jonathan Raider is a postdoctoral research associate in biology at the University of North Carolina Chapel Hill. Thanks so much for being with me today. You're very welcome. It's been an honor to be here. Thank you.

The deepest parts of the ocean are home to some of the most incredible creatures. on our planet. Though it's dark and cold, you've got things like anglerfish, bioluminescent jellyfish. It can feel like a completely different world. And the creatures down there don't just look different. They've developed unusual ways to survive the harsh conditions of the super deep. An international team of researchers recently discovered that some 13,000 feet below the surface, oxygen can be produced in a way that they weren't expecting without photosynthetic life. Small lumps called polymetallic nodules at the bottom of the ocean, were able to produce enough electricity to break down water and make oxygen.

That challenges the idea that photosynthesis is necessary to produce much oxygen. But while it gives some answers as to how life can thrive at the bottom of the sea, it also raises a whole load of new questions. Here to answer some of them is the lead electrochemist of that research team, Dr. Franz Geiger. He's the Charles E. and Emma H. Morrison, Professor of Chemistry, at Northwestern. Welcome to Science Friday, Dr. Geiger. Thank you so much. and thank you for covering this exciting story.

Oh, it's our pleasure. It's very cool. Tell me up a little bit about how the team came to this discovery. This goes back about 10 years when the lead author on this work, Professor Andrew Sweetman of the University of Highlands and Islands and Scotland, had a interesting discovery that he didn't believe, which was that when they analyzed oxygen readings down below at the abyssal seafloor, the oxygen increased over time. And that shouldn't have happened because there was no light to produce photosynthesis.

It's completely dark down there. And the surprise was such that the team decided this can't be right. And they didn't believe they were data for a long time. And kept going on tours out in the ocean, repeating measurements with different instrumentation and getting the same increases in oxygen as they did in the first set of measurements. And so Andrew contacted me about a year ago and had read a paper of ours that we published on electricity generation on metallic nanolayers. And I said, I don't think that's enough power that can lead to the electrolysis of water or water splitting. You need about one and a half volts or one volt for that for seawater.

And our earlier paper had shown only 10 millivolds 100 times or 10 times smaller voltages. But I said, why didn't you send some samples and the rest is history? So what are these polymetallic nodules? Would I know one if you put one on my desk? What does it look like? They are fascinating structures. They look like truffle, large truffles, for which you would pay a king's ransom, but they don't have the nice aroma.

They are not as dense as a big chunk of metal, let's say iron of the, same size, but much lighter. Many people liken them to a potato. They have about that size on average. And when you go down there and take pictures with the camera that's got a light attached to it, because again, it's completely dark otherwise, you see hundreds and hundreds of miles off these nodules on the seafloor. They look like a sack of potatoes thrown on the floor. Yeah. Where do they come from? How does one of these nodules form in the first place? they come from the ocean. Believe it or not, we've got many metals in ionic form that are dissolved in seawater. And that goes back hundreds of millions of years. And under the conditions of high pressure and low temperature

that are met down there at three to four kilometers depth, over the years, these ions precipitate out onto sharp objects. often it's literally a shark tooth that has fallen to the ground from high above. And many times people in fact find those nucleation sites, shark teeth from 10, 20, 50 million years ago at the center of one of these nodules. And they grow at about one millimeter per one million years. That's very slow. And given the size and isotope measurements, et cetera, that can determine their age, they're about 100 million years old.

The one I have in my lab and that we did measurements on that set of samples is about 100 million years old. It's the oldest thing I've ever worked with in my lab. It's absolutely fascinating. Wow. So you've got deep seawater. You've got your 100 million-year-old potato. How does that work into oxygen production?

What's the actual process going on here? We hypothesized that it's because of electrochemistry. And the reason is that when Andrew had... sent his nodules to us. We used this high sensitivity volt meter that we used for our previous study and attached it to platinum electrodes that we then attached to the nodules sitting inside a beaker that simply had ocean water simulant in it. And the readings were off the charts. I had expected a few millivolds at most. We read 50 millivolds, 150 millivoles. We read 50 millivoles. 950mmivolts, so close to what you get out of the double A battery, which is the classic

kindergarten or high school experiment that people do in a science class where you take your battery, you hook it up with wires and stick the wires into salt water. And on one side you get hydrogen bubbles coming out. On the other wire, you get oxygen bubbles coming out. Now, our sensors were only sensitive to oxygen. They were not sensitive to hydrogen. So we have evidence for oxygen production through those sensors, meaning evidence for what is called the oxygen evolution reaction.

That's one half of water splitting. And how that exactly occurs within the nodules, we hypothesize is because of the layered structure of the nodules. When you cut one open, it almost looks like an onion or perhaps a tree. So it's got a ring structure where there's more cobalt. Delt deposited for the first 10 million years, then manganese, the next 10 million years, a little bit more iron the next 10 million years. And so every time you've got these gradients of metal concentrations, you effectively have a

battery that's been known since Alessandro Volta, when he built the, will take, pile, over 200 years ago. Wow. So these nodules are sort of acting like their own batteries. If I did my kindergarten-level science experiment and hooked one up, would I actually see bubbles coming off of these potatoes, how much oxygen are they producing? The bubbles are seen when you take the nodules and water from the ocean floor, again, at these very, very high pressures to the surface. Professor Sweetman has done that measurement,

and you can see once you vent that benthic chamber, that instrument that collected the nodules with the water, it looks like a glass of sparkling water. Down at the ocean's floor, the pressure, are so enormous and the temperatures so low that oxygen does not bubble out of these nodules. Oxygen dissolves into the seawater. The solubility goes up with pressure. And just like sugar dissolves in the water, the oxygen will dissolve in the water. So no bubbles are seen, but you can still measure them using the oxygen sensors that we have. So what does this discovery mean in terms of chemistry and deep ocean research? How does it challenge preconceived notions here? It does so in a number of ways, and we're in the process of putting grant proposals

together for a variety of institutions, because this is obviously opening up lots of questions, as you indicated in your introduction. The nice thing is that the picture now is less murky than what it was before, because we have this new information, but we don't know, for example, the rates at which oxygen is produced, so we don't know how it competes with other oxygenation pathways, such as photosynthesis. We also don't know whether the nodules are all. always active through their entire lifetime, or if they have active periods that may have lasted for a million years, 50 million years ago, but are now inactive. And other ones that we are currently active only came to life, so to say, maybe a million years ago. The other thing we don't

know is whether or not that oxygen could act as a source for living organisms at this very diverse area of the ocean, which is the abyssal seafloor. Should I be thinking of these nodules as something like a battery that is being consumed in the course of this electrochemical reaction, or is it a catalyst that just facilitates the reaction? That's an excellent question, and one of the center questions we have here in one of the proposals that we're currently putting together, and we don't know the answer yet. It's likely that these structures are active for some time and then deactivate, which means that if they're catalytic in nature, that extent of catalytic action is time-dependent. It could also be that it's just simply acting as a

battery, and at that point, just like any battery, will empty out at some point, some of these nodules, or many of them will probably not be active today. So I know that there are companies that have proposed doing deep-sea mining, essentially, to gather these nodules. Do you think that that's an environmental risk if these nodules might be providing valuable oxygen to the deep-sea environments? We hope that this study will inform on when, where, and how to mine if mining licenses are given out. It's important to state that no mining licenses have been issued, but only exploratory licenses. This is a classic dilemma. We desperately need the minerals for preparing the energy transitions out of a fossil fuel economy into one that's powered by batteries.

And at the same time, if we open up the seafloorferm mining, again, we hope that the study informs on how to do that with the least environmental and biological and ecological impact. So if this is a sort of previously unknown way of producing oxygen on Earth, might this tell us anything about other planets? Like, if you see free oxygen in a planet's atmosphere, it doesn't necessarily have to have come from life. Correct. So we are very excited about the possibility of having ocean-bearing moons that have been hypothesized to exist with lots of evidence for it, but that are coated by thick shields of ice. Of course, those oceans are entirely dark. So it could be that we now have a double dark scenario where there's dark oxygen being produced in dark oceans on moons that perhaps could serve as an oxygenation form of life on those planets or moons. So what do you want to learn next about this?

What's the next step here? I'm very excited about seeing whether or not there might be a blueprint down there at the bottom of the ocean in these nodules to help us build better catalysts here at the Earth's surface. Many of us in the sciences are working on better water splitting catalysts. The best ones are platinum group elements. They're very rare. So that's not going to be promising for the energy transition. The metals that are electrochemically active in the nodules are common. nickel, iron, manganese, cobalt, and we think that there might be a plan that we can pursue

to build such structures up here. Dr. Franz Geiger is the Charles E. and M.H. Morrison Professor of Chemistry at Northwestern University. Thanks so much for taking time to talk with me today. Thank you so much. I really appreciate being on Science Friday. And that's it for today. A lot of folks helped make the show happen, including Rasha E.Ridi. D. Petersman. Shoshana Bucksbaum.

And many more. Next time, why so many people seem to be catching COVID this summer and how you can keep safe. But for now, I'm SciFri producer Kathleen Davis. See you then.