Moreover, the Arctic ecosystem is already threatened by the profound environmental upheavals caused by the climate crisis. It is known to change behaviors, growth, fecundity and mortality rates in organisms and many plastic chemicals are known toxins to humans," says Steve Allen, OFI Dalhousie University, a research team member. "Micro and nano plastics have basically been detected in every place scientists have looked in the human body and within a plethora of other species. Microplastics have already been detected in human intestines, blood, veins, lungs, placenta and breast milk and can cause inflammatory reactions, but the overall consequences have hardly been researched so far," reports Melanie Bergmann. This means that they are also exposed to the microplastics and chemicals contained in it. "People in the Arctic are particularly dependent on the marine food web for their protein supply, for example through hunting or fishing. 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 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 this way, it can also enter the food chain here when the zooplankton is eaten by fish such as polar cod and these are eaten by seabirds and seals and these in turn by polar bears. 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 an earlier study with AWI participation shows. Since the ice algae are an important food source for many deep-sea dwellers, the microplastic could thus enter the food web there. Once entrapped in the algal slime they travel as if in an elevator to the seafloor, or are eaten by marine animals," explains Deonie Allen of the University of Canterbury and Birmingham University, who is part of the research team. "The filamentous algae have a slimy, sticky texture, so it potentially collects microplastic from the atmospheric deposition on the sea, the sea water itself, from the surrounding ice and any other source that it passes. The surprising result: the clumps of algae contained an average of 31,000 ± 19,000 microplastic particles per cubic meter, about ten times the concentration of the surrounding water. The partners from Ocean Frontier Institute (OFI), Dalhousie University and the University of Canterbury then analyzed these in the laboratory for microplastic content. On an expedition with the research vessel Polarstern in summer 2021, she and a research team collected samples of Melosira algae and the surrounding water from ice floes. With the Melosira taking microplastics directly to the bottom, it helps explain why we measure higher microplastic numbers under the ice edge," explains the AWI biologist. Marine snow, on the other hand, is slower and gets pushed sideways by currents so sinks further away. "The speed at which the alga descends means that it falls almost in a straight line below the edge of the ice. 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. "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," Melanie Bergmann reports. Melanie Bergmann from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) has now published their findings. In addition to food, however, these aggregates also transport a dubious cargo into the Arctic deep sea: microplastics. There they form an important food source for bottom-dwelling animals and bacteria. When the cells die and the ice to whose underside they adhere melts, they stick together to form clumps that can sink several thousand meters to the bottom of the deep sea within a single day. It is a food lift for bottom-dwelling animals in the deep sea: The alga Melosira arctica grows at a rapid pace under the sea ice during spring and summer months, and forms meter-long cell chains there.
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