The alga Melosira arctica, which grows under the sea ice in the Arctic, accumulates very strongly in microplastics and contains ten times as many particles as the surrounding seawater. A research team led by the Bremerhaven Alfred Wegener Institute (AWI) reports in the journal “Environmental Science and Technology” that this poses a danger to organisms that feed on the algae. On an expedition with the research ship Polarstern in the summer of 2021, the scientists took samples of the algae and the surrounding water from ice floes.

“The filamentous algae have a slimy-sticky texture, so they potentially collect microplastics from atmospheric precipitation, the seawater itself, the surrounding ice and any other source they encounter,” explained Deonie Allen of the University of Canterbury and Birmingham University, which is part of the team, according to an AWI release.

The Melosira alga grows rapidly under the sea ice in the spring and summer months, where it forms meter-long chains of cells. If the algae contaminated with microplastics die and the ice on whose underside they are stuck melts, they stick together in clumps. These can quickly sink to the bottom of the arctic deep sea. “We have finally found a plausible explanation as to why we always find the largest amounts of microplastics in the area of ​​the ice edge, even in deep-sea sediment,” emphasizes AWI biologist Melanie Bergmann. The algae are an important food source for the bottom-dwelling animals and bacteria, it said.