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ANNOUNCER: You’re listening to Short Wave from NPR.
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REGINA BARBER: Around 20,000 years ago, the world was cold. Temperatures around the world averaged 10 degrees Fahrenheit cooler than they are today, and most of North America was covered in ice. Humans were surviving, though, mastering fire and making friends with wolves.
FRANKIE PAVIA: There’s places where the ice is a kilometer thick sitting on top of North America, the Northern US, and Canada.
BARBER: That’s Frankie Pavia, a geochemist at the University of Washington. And he says because the Earth’s climate was so different during that time, the winds and oceans moved differently than they do now.
PAVIA: And the sort of background state of Earth’s climate, right, is just different as a result both of these changes to the Earth’s surface and, right, because there’s 100 parts per million less carbon dioxide in the atmosphere during this time.
BARBER: But in the couple thousand years to follow, carbon dioxide levels in the atmosphere and temperatures started to climb, and the Earth’s climate began to change.
PAVIA: It’s a transition period. It’s trying to get itself back to sort of a stable baseline state.
BARBER: Today, our climate is changing, too. But to understand that and the amount of ice we’re losing, we need to know more about the past. That’s where Frankie comes in.
PAVIA: We’re trying to figure out how ice coverage in the Arctic Ocean responds to climate change events in the past. Sea ice in the Arctic is a really fundamental part of the Arctic system as a whole, and it’s declining quite quickly. And we would like to be able to predict what ice is going to be like in the future as we continue to warm the planet with fossil fuels.
BARBER: So naturally, Frankie wondered, what if space could help us know more about Earth, specifically using something called cosmic dust?
PAVIA: Cosmic dust is a debris that forms from collisions of things like asteroids and comets in the solar system.
BARBER: Cosmic dust blankets Earth’s surface at a constant rate. And Frankie realized that this material from space could be key to finding out how the Arctic ice is melting now.
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BARBER: So today on the show, what space dust is telling scientists about the history of ice in the Arctic and what that could tell us about the Earth’s future. I’m Regina Barber. And you’re listening to Short Wave, the science podcast from NPR.
BARBER: So Frankie, in a new study, you and your team try to figure out how Arctic ice basically covered the Earth and how it’s impacted by climate change. How do you get the sediment to study that?
PAVIA: Yeah, so to get the sediment, you have to send a boat out, right, to the part of the ocean where you want to collect mud. And essentially, what you’re doing is, you’ve got a big tube on the end of a long wire with some weight on top of it and a little device that self-closes at the end of it, so that when you fill up that tube with mud, the mud doesn’t all come sliding out when you raise it back up. And so you basically ram a big tube into the seafloor, fill it up with mud, right, with the oldest mud at the bottom and the youngest mud at the top. And then you haul that sediment back up to the ship that you’re on.
BARBER: If I was to look at these tubes, how big would they be?
PAVIA: The diameter of the tube is probably a little bit smaller than your or my face. And the length of the tube can vary from anywhere from, like, a foot to hundreds of feet long.
BARBER: How are you analyzing these? Like, are they, like, in a lab, and you’re, like, looking at them? Or, like, how are you studying them?
PAVIA: OK, so the sediments are taken– you know, raised up. They’re processed either on the ship or on land. They’re sort of sliced up about a centimeter at a time. And each layer, right, each of those centimeter-layers is analyzed to figure out what time period that that mud is from and what sort of characteristics of the environment are recorded in the chemical signatures of that sediment.
BARBER: OK, so you’re basically, like, going into, like, the database and, like, looking at, like, information from all of these, like, centimeter-thin disks.
PAVIA: Yeah, so–
BARBER: Wow.
PAVIA: –there’s– you know, there’s– there are repositories. There’s basically huge libraries of mud that’s been collected at the sea floor since the 1950s, more or less. Arctic mud is– hasn’t been getting collected quite as long as that. But right across the global ocean, you know, since the 1950s, and even back to, like, the Challenger expedition in the 1800s, people were taking samples–
BARBER: Wow.
PAVIA: –of seafloor mud.
BARBER: Wow. How much time is represented in this database of these, like, centimeter disks?
PAVIA: From these sediment cores specifically that we worked on in this paper?
BARBER: Yeah.
PAVIA: We are going back about 30,000 years.
BARBER: Wow. OK. And in your study, you looked at something called cosmic dust inside the sediment cores. And cosmic dust is that debris that forms from collision of things, like asteroids and comets in the solar system. How does this debris help you determine the age of ice?
PAVIA: Yeah, so when that debris forms, right, it gets bombarded with the solar wind, which is, right, blowing out from the sun. And it’s enriched in rare forms of helium because the sun is burning hydrogen to make helium. And so that helium, with a sort of distinct fingerprint, gets implanted into these cosmic dust grains. And those cosmic dust grains enter the Earth’s atmosphere. So when they come in, they get heated. And only the really tiny grains, you know, less– you know, about 1/100 of a millimeter, keep their distinct helium fingerprint. And, you know, these cosmic dust grains then blanket Earth’s surface at a constant rate in space and time over hundreds of thousands of years. And we can use measurements of that distinct helium fingerprint to tell us about how much cosmic dust is in sediment layers in the past.
BARBER: And knowing how fast it settles on the sea floor depends on how much ice was covering that area. How do you figure that out?
PAVIA: So I was actually studying cosmic dust in a part of the ocean that had nothing to do with ice. And I was using it in concert with one other sort of chemical index that we measure that nominally both tell you the same thing about how sediments accumulate at the seafloor. But they have different sources. So cosmic dust comes from space, through the atmosphere to Earth’s surface. And the other index chemical marker that we were looking at is produced in seawater. And when you have ice covering the Arctic, that cosmic dust that’s coming in through space and then through the atmosphere gets intercepted by the ice and can’t reach the seafloor. And we can detect that by measuring both our radioactive index and our helium fingerprint for cosmic dust.
BARBER: Yeah. What did you find?
PAVIA: Yeah, so, right, I got together with my main sort of collaborator on this, Jesse Farmer, who’s a professor at UMass Boston. And he had been working on Arctic climate change in the past for some years. And we were sort of spitballing this idea. And I was like, Jesse, is this, like, a good idea? Is this really dumb? Is there some way to, like– that we can get some Arctic sediments to test this? And Jesse–
BARBER: Mm, OK.
PAVIA: –like, had– Jesse sort of had the ideal set of samples for us to give this a whirl with.
BARBER: Just sitting around.
PAVIA: Yeah, truly. And so he sent me some little bags that had powdered sediment–
BARBER: Whoa.
PAVIA: –in them. Yep.
BARBER: And the Postal Service was not mad about that at all?
PAVIA: You know, this is sort of a funny thing when you’re shipping these sorts of things. You do have to be like, this is, you know, marine mud. It has no commercial value, blah, blah, blah. It doesn’t look as insidious or suspicious as you might think, but there are geologic samples that do.
BARBER: [LAUGHS] So you’re looking at these baggies, you’re looking at these samples, and you’re like–
PAVIA: Yeah.
BARBER: –is this method going to work?
PAVIA: So we maybe measured, like, 10 samples to compare the top of the core, right, the most recent interval, with samples that were from the last Ice Age, right, 20,000–
BARBER: OK.
PAVIA: –years ago. And we found sort of immediately that there was a big deficit in the amount of cosmic dust–
BARBER: Wow.
PAVIA: –based on helium, right, that we would have expected during the Ice Age.
BARBER: OK, so that amount that you would just assume would be, like, just accumulating on the– you know, on the ocean surface was just not right.
PAVIA: Yeah. There was, like, a 300% deficit in how much–
BARBER: Wow.
PAVIA: Yeah, exactly. And so that’s, like, in the world– in the world of, like, geochemistry and paleoclimate, that is, like– that is a real–
BARBER: That’s pretty concrete.
PAVIA: –that is a real big signal, right?
BARBER: Yeah.
PAVIA: And so that was, like– that’s what set us off to the races of, like, OK, we are– we might be on to something here.
BARBER: So this deficit in cosmic dust says there– you know, or implies that there was ice there. Why do we, as a human race, need to, like, know about the ice coverage during the Ice Age?
PAVIA: Yeah, so that helps us say, OK, we’ve had these major shifts in climate, including conditions in the Arctic that were a little bit warmer than today. How does sea ice coverage respond? Because we’ve seen that over that last 40, 45 years, ICE coverage in the Arctic has dropped by about 40%. And, right, climate models try and make predictions of when the Arctic will be ice-free. And an ice-free Arctic has consequences for things like shipping and navigation–
BARBER: Mm, yeah.
PAVIA: –for, right, geopolitics of Arctic-bordering countries that are jostling for superiority there for, right, fisheries, for coastal erosion of communities that live on Arctic coastlines. And so our goal is to figure out where there are major changes in climate in the geologic past that can help us, right, supplement the record of ice change that we’ve seen from satellites over the last 40 years, right, with longer timescales, with changes in climate that might be akin to where we’re heading in the not-so-distant future.
BARBER: So one of the findings that kind of surprised me is that what was melting the ice was maybe more clear than you thought. Like–
PAVIA: Well, it was and it wasn’t. We were able to rule out one, right? So in order to melt the– melt this ice, you got to bring heat in from somewhere, right? That’s what’s going to melt the ice. And we had a few options, right? One was heat from warm waters entering the Arctic from the Pacific. One was heat from warm waters entering the Arctic from the Atlantic. And one was heat from the atmosphere. And based on the timing of when the Bering Land Bridge opened up and allowed Pacific waters to enter the Arctic, we could show that heat from Pacific waters entering the Arctic was not the cause of this ice breakup. And so that left us with atmospheric warming, so direct atmospheric heating, or heat coming in from Atlantic waters. And we can’t conclusively, you know, make a call between Atlantic-sourced heating and atmospheric heating. But more work that tries to unpack, right, the mechanism for how you deliver heat to break up sea ice coverage during past Arctic climate change events would be really, really important to understand how that might be affecting ice coverage today.
BARBER: So we’re going to use your method more, and we’re going to find out more.
PAVIA: Yeah, and other methods, right? Like, other reconstructions that are looking at how different processes in the Arctic work.
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PAVIA: It takes a really holistic understanding of, right, a lot of different things in the climate system and how they all operate together.
BARBER: Frankie, thank you so much for talking with us today.
PAVIA: Yeah, thank you. This was fun.
BARBER: This episode was produced by Rachel Carlson with a little bit help from Hannah Chinn. It was edited by our showrunner, Rebecca Ramirez. And Tyler Jones checked the facts. Robert Rodriguez was the audio engineer. Beth Donovan is our vice president for podcasting. I’m Regina Barber. Thank you for listening to Short Wave, from NPR.
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