The Algae That Thrive in Arctic Darkness

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 https://www.awi.de/en/about-us/organisation/staff/single-view/clara-hoppe.html 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 [email protected] mailto:[email protected]! Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ atplus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://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 https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:00Speaker 00

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• 0:18Emily Kwong?

  You're listening to Short Wave from NPR.

• 0:23Emily Kwong?

  Hey, Shortwavers, Emily Kwong here, and today we are headed north to Norway, the land of the midnight sun.

• 0:31Speaker 02

  The sky 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 sunset.

• 0:40Emily Kwong?

  Because Earth rotates on a tilt, there is a period of time during the summer where the North Pole always faces the sun, 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.

• 0:58Speaker 02

  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.

• 1:13Emily Kwong?

  This is Clara Hoppe. She's a bio-geochemist 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 grayscale.

• 1:28Speaker 02

  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 and the moon. It's really quiet.

• 1:44Speaker 02

  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.

• 2:01Speaker 02

  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.

• 2:17Emily Kwong?

  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.

• 2:30Speaker 02

  The most intriguing and beautiful group of organisms that we found are diatoms. They are a group of microalgae that build these little boxes out of glass, out of silica, that they use as grazer protection.

• 2:49Emily Kwong?

  Clara thought that these microalgae might be the key to understanding the limits of photosynthesis. That's the process used by plants and microalgae to turn light into food.

• 3:00Speaker 02

  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.

• 3:14Emily Kwong?

  You know, you describing this, what immediately comes to mind is limbo. Like, how low can you go?

• 3:20Speaker 02

  Yes.

• 3:20Emily Kwong?

  It's almost like you were studying photosynthetic limbo or something.

• 3:23Speaker 02

  Yeah, but we really didn't know how low they could really go.

• 3:29Emily Kwong?

  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 Short Wave, the science podcast from NPR.

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• 5:04Emily Kwong?

  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?

• 5:21Speaker 02

  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.

• 6:06Emily Kwong?

  Is it almost like hibernation?

• 6:08Speaker 02

  Yes.

• 6:08Emily Kwong?

  Were people thinking they crawled into their ice caves and just kind of went to sleep?

• 6:12Speaker 02

  Yeah, exactly.

• 6:13Emily Kwong?

  And then what happened when springtime comes around?

• 6:17Speaker 02

  So they get, the light comes back, and the light serves as a cue to emerge from this resting stage, from their little cave.

• 6:27Speaker 02

  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.

• 6:38Emily Kwong?

  Right. And you set out to find those microalgae that were more active to challenge this traditional view of microalgae 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?

• 6:56Speaker 02

  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.

• 7:26Emily Kwong?

  Oh, OK, that makes sense.

• 7:28Speaker 02

  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.

• 7:39Emily Kwong?

  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?

• 8:05Speaker 02

  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 cored.

• 8:20Speaker 02

  We drilled cores out of the ice floe

• 8:23Emily Kwong?

  Whoa.

• 8:24Speaker 02

  to study which algae are there and in which physiological state.

• 8:29Emily Kwong?

  Science is fun.

• 8:30Speaker 02

  Yeah.

• 8:30Emily Kwong?

  Okay, so you're you're out there gathering ice, gathering seawater. Where is this all happening?

• 8:38Speaker 02

  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 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.

• 9:06Emily Kwong?

  Ocean City is like a different location on the ice where you all gathered samples.

• 9:09Speaker 02

  But it meant us dragging hundreds and hundreds of liter of water over the floe, 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 the snowstorm to the boat. So it was a lot of physical work involved getting those samples.

• 9:36Emily Kwong?

  Wow, science is not fun sometimes, actually.

• 9:39Speaker 02

  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 humid conditions. So I much rather do that at minus 20.

• 9:47Emily Kwong?

  Absolutely. So what did you find within these samples? What was the biggest finding?

• 9:52Speaker 02

  So the biggest finding for me was this super early increase in the biomass and activity of these microalgae. 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.

• 10:14Emily Kwong?

  So the microalgae were growing?

• 10:16Speaker 02

  Yes, they were growing.

• 10:18Emily Kwong?

  That's so cool. And just such a big deal that you found evidence of photosynthesis more north in 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?

• 10:55Speaker 02

  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.

• 11:09Speaker 02

  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.

• 11:20Emily Kwong?

  So Clara, how are microalgae able to do this? How are they able to, you know, fire up their photosynthetic engines the moment the tiniest bit of light hits?

• 11:32Speaker 02

  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.

• 12:10Emily Kwong?

  Oh, can you give me an example of one of those mechanisms that might give them that background energy?

• 12:15Speaker 02

  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.

• 12:32Emily Kwong?

  Oh.

• 12:33Speaker 02

  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.

• 13:01Emily Kwong?

  They're like omnivores. They like eat plants and meat.

• 13:04Speaker 02

  Yes.

• 13:04Emily Kwong?

  Or something.

• 13:05Speaker 02

  I think they do whatever they can to like, you know, fill up their energy reserves.

• 13:11Emily Kwong?

  They're the ultimate survivors. Well, this is just such a paradigm shift from what has been said 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?

• 13:29Speaker 02

  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, and then you're in this, what is, you know, the magical science location where you are like, wow, I don't understand this at all. And there are 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.

• 14:12Emily Kwong?

  Yeah. And that maybe the wintertime ocean is just far more alive than people thought.

• 14:19Speaker 02

  Yeah.

• 14:21Emily Kwong?

  Clara, thank you so much for coming on Short Wave to talk about this.

• 14:25Speaker 02

  Thank you for the interest.

• 14:29Emily Kwong?

  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 [email protected]. 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 Donahue. 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 Short Wave, the science podcast from NPR.

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