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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.”
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