Microplastics have long been found in all seas and even in the supposedly untouched deep sea. Measurements in the Fram Strait between Greenland and the Spitsbergen archipelago now show that the sediment of this Arctic sea region has particularly enriched these small plastic particles. This is due to ocean currents that bring and concentrate microplastics from other ocean areas.
Our plastic waste pollutes even the most remote areas of the world. Because the plastic hardly biodegrades, it remains in the environment for centuries and gradually breaks down into smaller and smaller particles. At the end of this development is microplastics – plastic particles, fibers, pellets and other plastic fragments that are smaller than five millimeters. Microplastics can also be released from textiles or cosmetics and from the abrasion of car tires.
13,000 microplastic particles per kilogram of sediment
Microplastics can now be found even in the ice of the polar regions or in the deepest deep-sea trenches on earth. How it gets there and where it stays has now been investigated by mine Tekman researchers from the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI) in Bremerhaven by measurements in Framstrasse. This sea area lies between the north-east coast of Greenland and the Spitsbergen archipelago and comprises a deep sea channel up to 5600 meters deep, in which two opposite ocean currents flow close together as if on a motorway. The Framstrasse is the only deep water connection between the Arctic and the Atlantic Ocean. In this marine area, Tekman and her colleagues have now systematically taken samples from various water depths and from the sediment in order to determine the microplastic load.
Analysis of the samples from the Arctic deep-sea observatory HAUSGARTEN showed: While the free water in Framstrasse contains rather average amounts of plastic particles, the load on the sediment is extraordinarily high: Investigations in a Fourier transform infrared spectrometer (FTIR) showed a load of up to 13,000 microplastic particles per kilogram of sediment, as the researchers report. This is up to 16,000 times higher than in the water column above. Almost all common plastics were represented in this microplastics, from polyamide from textiles and fishing nets to synthetic rubber from automobile and device construction or sealants to ethylene vinyl acetate from coatings, varnishes, paper, packaging or shoe soles. Particles from chlorinated polyethylene (CPE), a plastic that is used, for example, in the manufacture of cables, hoses, foils and anti-lock braking systems (ABS), were particularly well represented in the deposits on the sea floor.
More than half of all identified plastic particles were smaller than 25 microns, as reported by Tekman and her colleagues. This size corresponds approximately to half the diameter of a fine human hair. “This high proportion of such small particles really gives us food for thought, because of course the question immediately arises as to how animals react to these tiny plastic residues,” says Melanie Bergmann from AWI.
Entered from two directions
But where does all that microplastics come from? The scientists determined this using a flow model. This showed that the plastic particles from both the Arctic and the southern North Atlantic are introduced into the marine region. Most of the plastic particles stored on the seabed come from distant regions. Accordingly, the East Greenland current from the Arctic primarily introduces ethylene vinyl acetate, a plastic that is used for coatings, lacquers, paper, packaging or shoe soles, among other things. This plastic could have entered the water over melting sea ice. The Westspitzbergen Stream, on the other hand, carries plastic particles from marine areas south of Spitsbergen to Framstrasse. This finding was also reflected in the plastic mix of the corresponding samples, as reported by Tekman and her colleagues.
On their way to Framstrasse, the plastic particles gradually drift down and accumulate on the sea floor. Depending on the particle size, the type of plastic, the sinking speed and the water depth, some particles have already traveled up to 650 kilometers before they reach the sea floor. “The idea that microplastic particles could sink into the depth fairly quickly and almost vertically has been refuted by our model results,” says Bergmann. “The large amount of particles and the large number of different types of plastic in the sediment show that microplastics accumulate continuously on the sea floor of Framstrasse. That means the deep sea of this marine region is a repository for microscopic plastic particles. “
The researchers now want to investigate how the volume of microplastics in Framstrasse changes over the course of the year. To do this, they rely on so-called sediment traps, which are anchored in the Arctic AWI deep-sea observatory and capture all year round what sinks as particles or sea snow from the water surface into the depths. “The study that has now been published is an important snapshot in which we were able to get a good overview of the plastic load on Framstrasse with analyzes in the infrared microscope,” explains Bergmann’s colleague Gunnar Gerdts. The future measurements should then also provide an overview over time.
Source: Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research; Technical article: Environmental Science & Technology, doi: 10.1021 / acs.est.9b06981