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It is a food elevator for bottom-dwelling animals in the deep sea: the algae melosira arctica grows rapidly under Arctic sea ice in the spring and summer and forms metre-long cell chains. When the cells die and the ice melts, they stick together to form clumps that can sink several thousand metres to the bottom of the deep sea within a single day. There, they form an important food source for animals and bacteria.

In addition to food, however, these aggregates also transport a dubious cargo into the deep Arctic sea: microplastics.

A research team led by biologist Dr. Melanie Bergmann from Germany's Alfred Wegener Institute (AWI) and researchers at Dalhousie University and the University of Birmingham has outlined this finding in the journal Environmental Science and Technology. 

“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,” Dr. Bergmann says.

Until now, the researchers only knew from earlier measurements that microplastics concentrate in the ice during sea ice formation and are released into the surrounding water when it melts. The speed at which the algae descends means that it falls almost in a straight line below the edge of the ice.

The research team collected samples of the algae and the surrounding water from ice floes during an expedition with the research vessel Polarstern in the summer of 2021.

Steve Allen of the Ocean Frontier Institute at Dalhousie analyzed them for microplastic content, finding that the clumps of algae contained about 10 times the concentration of the surrounding water.

“Micro- and nanoplastics have basically been detected in every place scientists have looked in the human body and within a plethora of other species. It is known to change behaviours, growth, fecundity and mortality rates in organisms,” says Dr. Allen.

Since the ice algae are an important food source for many deep-sea dwellers, the microplastic could enter the food web there. But it is also an important food source at the sea surface and could explain why microplastics were particularly widespread among ice-associated zooplankton organisms, as shown in an earlier study AWI participated in. In this way, it can also enter the food chain here when the zooplankton is eaten by fish, such as polar cod which are eaten by seabirds and seals and in turn by polar bears.

“The filamentous algae have a slimy, sticky texture, so it potentially collects microplastic from the atmospheric deposition on the sea, the sea water itself, the surrounding ice and any other source that it passes. Once entrapped in the algal slime, they travel as if in an elevator to the seafloor, or are eaten by marine animals,” explains research team member Deonie Allen of the University of Canterbury and Birmingham University.

The detailed analysis of plastic composition showed that a variety of different plastics are found in the Arctic, including polyethylene, polyester, polypropylene, nylon, acrylic and many more. In addition to various chemicals and dyes, this creates a mix of substances whose impact on the environment and living creatures is difficult to assess.

The researchers say this should be prioritised in the global plastics agreement being negotiated. Dr. Steve Allen is part of the scientific advisory group assisting with the negotiations.

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Original Publication:

Bergmann, M., Allen, S., Krumpen, T., Allen, D., 2023. High levels of microplastics in the Arctic ice alga Melosira arctica, a vector to ice-associated and benthic food webs. Environmental Science and Technology. DOI: https://doi.org/10.1021/acs.est.2c08010

Printable images can be found in this collection until the end of the embargo: https://multimedia.awi.de/medien/pincollection.jspx?collectionName=e6d8e14936224838b631562f11db3257#1681829133242_1 and then in the online version of this press release at https://www.awi.de/ueber-uns/service/presse.html
Video footage of the sampling for the study can be found here: https://we.tl/t-9p7yre7Ro1

Author contacts:

Dr. Steve Allen, Ocean Frontier Institute, Dalhousie University
Phone: +64 (0)22 095 5171
Email: steveascotland@gmail.com

Dr. Melanie Bergmann, Alfred Wegener Institute
Phone: +49 (0) 471 4831-1739
Email: Melanie.Bergmann@awi.de

Dr. Deonie Allen, University of Birmingham, UK/ Canterbury University
Phone: +64 (0)22 095 5171
Email: deonie.castle@canterbury.ac.nz

Press officer:

Folke Mehrtens, Alfred Wegener Institute
Phone: +49 (0) 471 4831-2007
Email: medien@awi.de

Alison Auld, Dalhousie University
Cell: 1-902-220-0491
Email: alison.auld@dal.ca