Plastic pollution is now found in most places of the planet. Even in areas with little human activity, water masses transport microplastics that become part of the food web and threaten marine ecosystems.

While the Arctic Ocean is no longer considered plastic free, there are large knowledge gaps concerning where the plastic is coming from and how it affects organisms and their habitats.

The Eurasian Arctic is one of the most underreported areas. This is where we went in September 2019, with the R/V Akademik Mstislav Keldysh on its 78th research cruise.Researchers from different institutions in Norway, Russia and the UK worked on board to gather samples of floating plastic debris through the Barents, Kara, Laptev and East-Siberian Seas.

Microplastics are small pieces of plastic that can have very different chemical compositions (polymer types) and morphology (such as fibers, fragments or films). Their shape, size and weight can further help us identify where the plastic particles may come from.

If we could find out more about what drives plastic pollution and distribution of microplastics in the Arctic Ocean, we could contribute to the monitoring and mitigation of this issue. The project was partly funded by the Norwegian Ministry of Climate and Environment project ESCIMO, which aims to “Establish regional capacity to measure and model the distribution and input of microplastics to the Barents Sea from rivers and currents”. Russian ministries and foundation grants helped fund the project for similar reasons.

So how does the plastic end up in the Arctic Ocean in the first place?

The thermohaline circulation, also known as “the great ocean conveyor belt,” transports and mixes the waters of the world’s oceans. In particular, the currents transfer plastic from the North Atlantic to the Arctic and pollute the Barents Sea and the Greenland Sea. The Arctic rivers can also be potential sources. Further, microplastics transported in the Artic sea ice and released when the ice melts, may be another important pathway.

As we know from Asian countries, most of the plastic pollution in the worlds’ oceans come from just a few rivers that wash enormous amounts of waste into the ocean. But as far as we knew, there weren’t any data on transportation of plastic pollution by Siberian rivers into the Arctic Ocean.

By comparing samples from the different areas, we could analyze the distribution of microplastics in connection with oceanographical properties.

During the cruise, we collected a total of 48 samples from the surface water using a Neuston net. We also collected 60 subsurface samples by using a ship-board underway pump-through system with an intake 3 meter below the surface. Installing this underway system was particularly challenging, because the collection of microplastics was accompanied by measurements of oceanographic characteristics, such as temperature, salinity, turbidity, dissolved oxygen and so on.

The samples were taken from the Barents, Kara, Laptev and East-Siberian Seas. But the borders between these seas are not separating the different type of water masses that can transport and circulate microplastics in different ways. When analyzing the samples, we therefore also compared four main water masses: The Atlantic surface water, the Polar surface water and the Great Siberian rivers plumes, which we further divided into the inner and outer plumes.

What we wanted to find out was how much microplastics there were, the type of plastics, the properties of the particles and to identify their potential sources.

When analyzing the samples, we found that all areas and water masses had some amount of microplastics, except the surface samples from the Polar surface water. In general, the concentrations of plastics were relatively low. 12 of 48 surface water samples contained microplastics. In the subsurface samples, 50 of 60 contained plastics. We found on average 0.004 items of microplastics per m³ in the surface samples, and 0.8 items per m³ in the subsurface samples.

When analyzing the distribution of the different types of microplastics, we saw clear differences between the water masses. For example, the subsurface samples from the inner plumes were characterized by the highest abundance of fibers and an absence of fragments. Further, the microplastic characteristics (the abundance of fragments and the ratio of fragments/fibres) were statistically different between in the samples from the Atlantic surface water and in the riverine plumes.

This meant that we could distinguish between microplastics transported to the Arctic Ocean from the North Atlantic, and microplastics discharged from the Ob, Yenisei and Lena rivers. While these water masses have similar plastic concentrations (numbers of items per m³), the weight concentration of the particles was ten times higher for the Atlantic surface water than the river plumes.

By combining our observations of the distribution of microplastics and their different characteristics, we identified two main sources of microplastics to the Eurasian Arctic: Inflow from the North Atlantic and discharges from the Great Siberian Rivers.

In contrast to other places in the world, the role of rivers haven’t been considered that much when analyzing microplastics in the Arctic. Our data showed that the Great Siberian Rivers should be considered when trying to understand the distribution and potential sources of microplastics in the Arctic Ocean. We can also suggest that the properties of microplastics can be used to identify different sources and water masses.

We are very excited to publish these results. The detailed description of the methods of sampling and measurements can be used when organizing future studies of microplastics pollution. It is especially useful when organizing monitoring of microplastics in Russia.

We will also use the data to elaborate on mathematical models that will help us evaluate and understand more of the pathways of plastic pollution in the Arctic Ocean.

Read the full paper here: Microplastics distribution in the Eurasian Arctic is affected by Atlantic waters and Siberian rivers