Greenland Seabed Yields First Plastic Pollution History

Using so called seabed coring somewhat similar to the ice core drilling techniques used by glaciologists, researchers from the University of Copenhagen in cooperation with colleagues from Aarhus University have achieved the first historical record of plastic pollution on Greenland's seabed.

The record shows an increased accumulation of microplastics on the seabed since the 1950s, with significant fluctuations. While particular environmental conditions such as freezing weather and glacier discharge could play a role, interestingly such increases and decreases in plastic accumulation also align with historical socio-economic development in Greenland.

"Our data shows a concurrence between the construction projects and other socio-economic events that took place locally in Greenland during the country's modernization, and major increases in the amount of plastic accumulating on the seabed. As researchers in plastic pollution, we can use this knowledge to reassess the sources of plastic," says Ph.D Karla Parga Martinez from the Department of Geosciences and Natural Resource Management, who is currently a Postdoc at McGill University, Canada.

Seabed coring involves dropping a heavy metal sampler through more than 800 meters of water, hitting the seabed mud vertically.

The sampler tube is immediately filled with sediment layers of the seabed surface. It is then hauled to the surface revealing datable contents including plastics of various kinds.

A prevailing view has been that the majority of plastic comes to the Arctic via ocean currents, but the new data highlights that local sources also play a significant role. According to the researchers, this knowledge can help them refine the global data on plastic contamination.

"There is a strong desire among scientists to obtain high-quality data on plastic in the oceans, so we have a proper overview of the problem of plastic pollution, and also develop models to monitor where the trends are heading. This research project is an important step in that direction. For the first time we now have a historical overview from the Arctic region of this plastic pollution," says coauthor Dr. Nicole Posth, Associate Professor at the Department of Geosciences and Natural Resource Management.

This achievement could help push for new solutions by documenting the wide distribution of plastics across its production history.

"It is important to show that plastic is making its way to the ocean floor - that our actions directly influence our environment. We have ever-increasing evidence of plastic´s negative impact on ecosystem (and human) health. This is now a reality, we must explore the scope of, and new studies like this one is needed to provide the evidence," says Nicole Posth.

A method to be followed

The researchers developed refined methods of coring in the ocean sediments and identifying plastics by their polymer composition by analyzing the total contents of samples.

The age of the seabed samples is determined using so-called radionuclide dating.

Due to their rate of decay, using natural lead isotopes and artificial cesium isotopes - the latter being the result of nuclear weapons testing in the atmosphere in the 1960´s and with a half-life of around 30 years - it is possible to date the seabed and the plastics found in it to successfully determine its age.

By jamming a tube into the seabed, the researchers were able to retrieve cores of the seabed for analysis. These samples were dated using radionuclide dating, where decaying isotopes are measured to determine a materials age.

Slicing the cores into what corresponds to relatively short time periods and isolating the microplastics from the seabed components (sand, clay, organic debris etc.), they could then compare the plastic´s chemical composition to a library of known plastics from different ages.

Finally matching the microplastic type to the age of the seabed sediment from which it was extracted, they could build a record back in history.

According to the researchers such methodical refinements could end up playing a larger role in our understanding of plastic contamination in the world ocean as they could be applied in many other places globally and provide solid, more aligned global data.

"When we meet to communicate our results in the scientific community, we need to be able to "speak the same language", so broadly applicable methods and transparency about characteristics of the study sites are important, to be able to align results across the globe and between labs," says Posth.

Tangible evidence of the Anthropocene

The so-called Anthropocene refers to the period of Earth's recent history where human activity has affected the climate and ecosystems of our planet. The concept has become an accepted term in cultural and societal debates, but as a scientific concept, it remains controversial.

The Anthropocene is an unofficial and continuously debated period of geologic time defined as the period in Earth's history where human activity has had a significant impact on the planet's climate and ecosystems.

"It is not an accepted geological time period. However, plastic accumulation in the seabed is now a very tangible part of that discussion because we have an undeniable proof that humanity has left its geological imprint even in this remote location," says Dr Nicole Posth.

Plastic contamination of the oceans leave a human trace that is measureable on a global and historical scale, and one that we are only now beginning to understand the impact of.

"If we are to assess the consequences of our actions as a species to the biosphere we inhabit, understanding the geological history of our presence is necessary. That is why historical records of plastic contamination, such as the one we have created in West Greenland are important", the researcher concludes.