Short Wave - The Algae That Thrive in Arctic Darkness

Episode Date: March 26, 2025

Microalgae are tiny organisms that convert energy from sunlight into fuel. The arctic ecosystem depends on them. In springtime, the algae bloom brilliant shades of green and draw tiny crustaceans, fish, birds and more to arctic waters. But what happens in wintertime, when the sun goes down and darkness reins for months? In the depths of the polar night, biogeochemist Clara Hoppe has found evidence that some microalgae are still ready to photosynthesize. Today on the show: how tiny microalgae limbo for their lives and come out more powerful than scientists ever imagined. Want to hear more stories of nature pushing the boundaries of what scientists previously thought possible? Let us know by emailing [e-mail]!Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Hey, shortwavers, I'm Moli Quang here, and today we are headed north to Norway, the land of the midnight sun. This guy looks like cotton candy the whole day, because you have a sunrise that doesn't stop. It's just a full day of sunrise or a sunset. Because Earth rotates on a tilt, there is a period of time during the summer where the North Pole always faces the sun in creating a polar day, or perpetual sunlight. But in exchange, there's also a period of time during the winter of perpetual darkness. That's called the polar night. So the polar night is the period between the last sunset in fall and the first sunset in spring, during which the sun never rises

in the Arctic for several months. This is Clara Hopa. She's a biogeochemist at the Alfred Wegener Institute in Germany. But a lot of her fieldwork is based here around the Arctic Circle. During the polar night, she says, it's like everything is in gray scale. When it's really dark, it's really a black

and white world, I would say, where you see some gray shades of things and you see stars in the moon. It's really quiet. There's wind. There's instrument noise.

There's, you know, ship sounds and snowmobiles. But like natural sounds, it's probably mostly the wind and the snow moving. It's a very big, dark world. And because you're only seeing what you see with your little headlamp, you see very, very little, and you feel very small. In the winter of 2020, Clara, embarked on an expedition into the heart of the polar night. To study microalgae, these photosynthesizing microorganisms that are super small and delicate.

The most intriguing and beautiful group of organisms have we found are diatons. They are a group of microalgae that build these little boxes out of glass, out of silica, that they use as grazer protection. Clara thought that these micrology might be the key to understanding the limits of photosynthesis. That's the process used by plants and micrology to turn light into food. When there's absolutely no light, we can be sure that there is no photosynthesis. But we don't know how low this lower limit of light actually is where photosynthesis is possible. You know, you describing this what immediately comes to mind is limbo. Like how low can you go?

Yes. It's almost like you were studying like photosynthetic limbo or something. Yeah, but we really didn't know how low they could really go. So today on the show, we're headed into the polar night. How tiny microalgae

stare into the abyss limbo for their lives and come out more powerful than scientists ever imagined. You're listening to Shorewave, the science podcast from NPR. Clara, thanks to your work I have learned, that microalgae are found in the Arctic. They exist up there.

And for a long time, scientists thought that microalgae were basically dormant for much of the year. Can you tell me what the traditional thinking was about their existence? So the traditional thinking was very much when there is no light, there can't be active life of these microalgae.

So what people have assumed is happening is that these cells hibernate. So they are in a resting stage. Some of them form actual resting spores that are very durable. And then they can overwinter, for example, in the sea ice. So those resting stages can be frozen into the sea ice in the fall and then be stuck in the sea ice and then get released in the spring when the sun comes back. That was a very traditional way of thinking of microalgae up there in the high north. Is it almost like hibernation? Yes. Were people thinking they like crawled into their ice caves and just kind of went to sleep? Yeah, exactly. And then what happened when springtime

comes around? So they get, the light comes back and the light serves as a cue to emerge from, from this resting stage, from their little cave. And then they can, yeah, continue photosynthesizing and dividing again. And there are algae. microalgae that actually do that. It's just that it's not all of them. Right. And you set out to find those micrology that were more active to challenge this traditional view of micrology as these wintertime sleeping beauties. So in 2015, you set out on a research trip to the Svalbard Archipelago in Norway. What did you find up there? So when we looked at them in the microscope, we saw that they were active vegetative cells.

So they were loaded with chlorophyll. So the chlorophyll is the pigment that is used for photosynthesis and it's a big, costly compound in the cell. So we would have expected that

they wouldn't invest energy into this pigment in a period where they can't use it. Oh, okay, that makes sense. So seeing them so ready to photosynthesize, suggested to me that, you know, they were in this physiologically active stage and not in this resting stage. Right. So like, why were they active? So let's fast forward to 2020 and you find

yourself with an opportunity to do more research on photosynthesizing microalgae as part of the mosaic expedition. You went far north, even further north, aboard the polar stern, which is this ship wedged into a piece of Arctic sea ice that's just like floating along. How did you and your team go about measuring the activity of microalgae up there? So on a weekly basis, we sampled the microalgae in the water column, so in the water under the ice, and then in the ice itself. So we took water samples and we drilled, we drilled cores out of the ice flow to study which algae are there and in which physiological state. Science is fun. Yeah.

Okay, so you're out there gathering ice, gathering seawater. Where is this all happening? Yeah, so the water sampling initially happened mostly at a hole next to the ship, which was very convenient because then the samples were directly on the boat. But then in beginning of March, we had a lot of dynamics in the ice and it destroyed our hole. So we couldn't sample anymore. And then we moved to Ocean City, which existed throughout the whole winter. Ocean City is like a different location on the ice where you all gather examples.

But it meant us dragging hundreds and hundreds of liter of water over the flow, up the gangway and into the labs. So it was really, you know, us pulling those buckets and buckets of water on little pulkas or little sledges behind us through this. storm to the boat. So it was a lot of physical work involved, getting those samples. Wow, science is not fun sometimes, actually. Well, at least you can do it in the cold. You know, if people that work in the tropics have to do that in like hot human conditions. So I much rather do that at minus 20. Absolutely. So what did you find within these samples? What was the biggest finding? So the biggest finding for me was this super early increase in the biomass and activity of these macroalgae.

So we found just a few weeks after the first sunrise, we found the biomass of the microalgae increasing, both in the water column and the sea ice. So the microalgae were growing. Yes, they were growing. That's so cool. And just such a big deal that you found evidence of photosynthesis. more north than even darker conditions than you did in Svalbard back in the day. And a key part of this, of course, was working with scientists to measure the actual levels of light under the Arctic sea ice, the levels at which this photosynthesis was happening.

And you documented a very low level of light, about 0.04 micromoles per second per square meter. So why was that such a big deal that you caught that, that you caught Arctic microalgae photosynthesizing? at that low of a level. Because it's several orders of magnitude lower than what people usually assume, for example, what is put into those big global ecosystem and ocean models. And if this light level is really several orders of magnitude lower, that means that there is a lot more productivity in parts of the oceans that we thought wouldn't be productive.

So, Clara, how are micro-euroids? algae able to do this? How are they able to, you know, fire up their photosynthetic engines the moment the tiniest bit of light hits? I mean, they must be incredibly efficient. They must, yeah, transfer all that energy that comes in into biomass production. And I guess to some extent, we need to solve the riddle of what they actually do to survive the polar night, the proper darkness. But there seem to be a range of different mechanisms that allows them to survive the polar night. And those mechanisms don't respond to the increase in light, but they may give them some background energy that allows them to then start growing as soon as the light comes back.

Oh, can you give me an example of one of those mechanisms that might give them that background energy? So phytoplankton, even though they do photosynthesis, they are not. only plants in a traditional way, we call them mixotrophs. So while they do photosynthesis, they can also eat like an animal. Oh, so some species can do something we call phagotrophy, which is basically eating bacteria or other small phytoplankton cells. And then other species can do, or probably most species can do something we call osmotrophy, which is taking up dissolved organic compounds from the seawater.

So dissolved sugars or amino acids or something like that. They're like omnivores. They like eat plants and meat. Yes. I think they do whatever they can to like, you know, fill up their energy reserves. They're the ultimate survivors. Well, this is just such a paradigm shift from what has been sad about Arctic life, polar nights and what's really going on in our ocean.

How has this shaped your view of the polar night and what's really going on there? I think it's mostly shaped a feeling of not knowing. I mean, if you have those paradigms and then you realize that they can't really explain your observations, then you're in this, what is, you know, the magical science. location where you are like, whoa, I don't understand this at all. And there's so many things I want to study and find out. So it's really, you know, the beginning of solving this riddle is understanding that it's a riddle. So you start thinking about a lot of different things that you haven't really been thinking before. And that's really the most fun. Yeah. And that maybe

the wintertime ocean is just far more alive than people. Yeah. Clara, thank you so much for coming on Shortwave to talk about this. Thank you for the interest. If you liked this episode, make sure you never miss a new one by following us on whichever podcasting platform you're listening from. And if you have a science question, you'd like us to investigate, send us an email at Shortwave at npr.org. This episode was produced by Hannah Chin and edited by our showrunner Rebecca Ramirez. Tyler Jones checked the facts. Robert Rodriguez was our audio engineer.

Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Emily Kwong. Thank you for listening to Shortwave, the science podcast from NPR.