AT THE SURFACE, the Arctic Ocean is pure serenity: chunk after chunk of bright-white ice, lazily floating around. What you can’t see is that its underside is covered in green snot, à la the ectoplasm from Ghostbusters—an underwater forest of Melosira arctica, algae that grow into sticky, dangling “trees” several feet long.
While not appetizing to you or me, Melosira arctica forms the foundation of the Arctic Ocean food chain. During the spring and summer, its individual photosynthetic cells grow quickly, absorbing the sun’s energy and forming long chains. These become food for small surface-dwelling critters known as zooplankton, which are in turn eaten by bigger animals, like fish. The clusters also detach and sink thousands of feet to feed sea cucumbers and other seafloor scavengers.
But now this algal ecosystem—like literally everywhere else on the planet—is thoroughly infested with microplastics, which ride on currents and blow in from faraway metropolises to settle on ice and snow. This is likely to have major consequences not just for Arctic organisms, but the way that the ocean sequesters carbon from the atmosphere. A paper published today in the journal Environmental Science and Technology finds that, on average, this algae is laced with 31,000 plastic particles per cubic meter—thanks to its gelatinous tendrils. “The algae form long strands or curtain-like structures and produce a sticky mucus that likely helps to trap microplastic particles efficiently from their surroundings,” says marine biologist Melanie Bergmann of the Alfred Wegener Institute in Germany, lead author of the paper.
Indeed, the concentration of microplastics (or particles smaller than 5 millimeters) in the algae is 10 times higher than the 2,800 particles the scientists found per cubic meter of water. Sea ice is even more contaminated: Bergmann’s previous research found 4.5 million particles per cubic meter. This astronomical figure is due to floating sea ice’s ability to “scavenge” particles from seawater as it freezes, all while getting dusted with atmospheric microplastics falling from above.
As Melosira arctica grows on this ice, its stickiness attracts microplastics from the surrounding water. Later, when the ice melts, those trapped particles are liberated, releasing a concentrated dose of microplastics. A whopping 94 percent of the microplastics the researchers found in the algae were smaller than 10 microns, or a millionth of a meter. “Because it’s a filamentous algae, and the cells are quite small, it’s collecting all the small stuff preferentially,” says Deonie Allen, a coauthor of the paper and a microplastics researcher at the University of Birmingham and University of Canterbury. “And all the really small stuff ends up making the biggest impact on the ecosystem.”
The smaller a particle is, the more organisms it can get into. Plastics can break down so small that they enter individual cells of either the algae or the zooplankton that feed on them.
The researchers can’t yet say if all that microplastic is harming Melosira arctica. But additional lab research has found that plastic particles can be toxic for other forms of algae. “In experiments with very high doses of microplastics, small microplastics damaged and entered algal cells, leading to stress responses such as damage of chloroplasts and thus inhibition of photosynthesis,” says Bergmann.
There’s another concern, too: If enough plastic gathers on the algae, it could block sunlight from reaching the cells, further interfering with photosynthesis and growth. “This study really does contribute to a growing body of research that shows that these microscopic organisms and these microscopic plastics can compound and become a really macroscopic problem,” says Anja Brandon, associate director of US plastics policy at the Ocean Conservancy, who wasn’t involved in the study. “This algae in the Arctic, and phytoplankton throughout the marine environment, make up the fundamental backbone of the marine food web.”
But the proliferation of plastic could devastate that web. As summer temperatures rise and the Arctic’s sea ice deteriorates, more and more algae clumps can break free and sink, carrying those microplastics with them into new ecosystems. That could be why scientists are also finding gobs of the particles in Arctic Ocean sediments. “There’s a whole community right underneath where the ice is melting,” says Steve Allen, a microplastics researcher at the Ocean Frontiers Institute and coauthor of the new paper. The sinking algae is a kind of “conveyor belt” of food to benthic creatures like sea cucumbers and brittle stars, he says.
In this sensitive ecosystem, nourishment is relatively scarce compared to, say, in a tropical reef. If a sea cucumber is already making do with limited amounts of food trickling down from the surface, it would be bad to load that food with inedible plastic. This is known as “food dilution” and has been shown to be a problem for other small animals, which fill up on microplastics while reducing their appetite for actual food.
Jagged plastic particles can also cause severe scarring of the gut, as was recently shown in seabirds with a new disease known as plasticosis. And that’s to say nothing of the potential chemical contamination to an animal’s digestive system: At least 10,000 chemicals have been used to make plastic polymers, a quarter of which scientists consider to be of concern.
Microplastic contamination of Melosira arctica could have serious effects on the carbon cycle, as well. As algae grows, it absorbs carbon, as plants do on land. When it sinks to the seafloor, it sequesters that carbon in the depths. But if microplastic inhibits their growth, the algae will absorb less of the stuff. Or if the pollutant makes the algae break apart more easily, that will give the scavengers in the water column more opportunities to consume it, thus keeping some of the carbon from reaching the seafloor. And if scavengers eat the plastic, even their waste may be less likely to make it to the bottom of the ocean: When scientists fed microplastics to zooplankton known as copepods in the lab, the particles made their fecal pellets slower to sink and easier to break apart. That’s bad both for carbon sequestration and for the animals that rely on this waste as a food source.
All of this feeds into the dramatic transformation of the Arctic, which is now warming more than four times faster than the rest of the planet. Atmospheric plastics that settle on sea ice—especially bits of black car tires—absorb more of the sun’s energy and may accelerate melt. That exposes more dark ocean waters, which absorb more heat and melt more ice. Altogether, there’s less sea ice, and therefore less space for Melosira arctica to do its carbon-absorbing work—and more melting, which releases a tide of accumulated plastics.
Bergmann thinks this situation will only get worse as a warmer Arctic leads to more human development, and therefore more plastic trash. “As the sea ice retreats, human activities in the region increase,” says Bergmann. “As a matter of fact, they already have—fisheries, tourism, shipping—which will perpetuate pollution.”