Microplastics Dominate Arctic Sea Algae! Contamination Spreads to Deep Sea, Marine Food Web, Finds Study

This filamentous algae is an important food source for animals as well as bacteria dwelling in the deep sea. It proliferates during summer and spring, forming metre-long chains of algal cells underneath the ice. When these cells die and the ice they call their home melts, these chains clump together and swiftly sink to the bottom of the sea within a single day, making up a full meal for the deep sea residents.

While they act like a 'food elevator' for the deep sea dweller, they also transport dubious, undesirable cargo to the ocean's depths: Microplastics!

Microplastics’ dive into deep sea

In the summer of 2021, researchers from Germany’s Alfred Wegener Institute went on an Arctic expedition. They compared samples of the algae Melosira and the surrounding water from floating ice, and the results shocked them. The clumps of dead algae contained an average of 31,000 ± 19,000 microplastic particles per cubic metre. This is about ten times as many microplastic particles as the surrounding seawater!

Until now, researchers only knew that microplastics concentrate in the ice during sea ice formation and are released into the surrounding water when it melts. But the current study demonstrated, for the first time, how Melosira alga takes microplastics straight to the depths of the ocean! As per the study, these algae could be the source of high microplastic concentrations under the edge of the ice and deep-sea sediments.

"We have finally found a plausible explanation for why we always measure the largest amounts of microplastics in the area of the ice edge, even in deep-sea sediment," says a coauthor of the study, Melanie Bergmann.

Possible journey up the food chain

The detailed analysis of plastic composition in the Arctic revealed the presence of polyethene, polyesters, nylon and acrylics, as well as some sinister chemicals and dyes — creating a complex cocktail whose exact impacts are challenging to quantify even for scientists.

As modern humans, we are exposed to immense amounts of microplastics on a daily basis. But for the dwellers of the pristine deep-sea ecosystem, the presence of microplastic could spell many unknown dangers. These arctic algae form the very base of the aquatic food web and are consumed by zooplanktons, which have also shown widespread microplastic infestation.

Further up the food chain, the zooplankton is eaten by fish such as polar cod, which are, in turn, consumed by seabirds and seals. Finally, the chain ends at the apex predators like polar bears or even humans. Thanks to biological accumulation, particularly the biomagnification of microplastics, the concentration of microplastics in animal tissue increases as we move up the food chain.

Micro and nano plastics have been detected in almost every place scientists have looked at — in plenty of animals and human bloodstreams, lungs, veins and even the placenta. Still, their long-term health consequences for humans remain uncertain.

The arctic sea ice is already on a roller coaster ride due to the climate crisis, and scientists fear that an added threat of microplastic exposure will only weaken the ecosystem!

This study was recently published in the journal Environmental Science & Technology and can be accessed here.

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