Arctic sea ice is an important temporal sink and means of transport for microplastic

Abstract

Microplastics (MP) are recognized as a growing environmental hazard and have been identified as far as the remote Polar Regions, with particularly high concentrations of microplastics in sea ice. Little is known regarding the horizontal variability of MP within sea ice and how the underlying water body affects MP composition during sea ice growth. Here we show that sea ice MP has no uniform polymer composition and that, depending on the growth region and drift paths of the sea ice, unique MP patterns can be observed in different sea ice horizons. Thus even in remote regions such as the Arctic Ocean, certain MP indicate the presence of localized sources. Increasing exploitation of Arctic resources will likely lead to a higher MP load in the Arctic sea ice and will enhance the release of MP in the areas of strong seasonal sea ice melt and the outflow gateways.

Fig. 1

Pathway and microplastic content of sea ice cores in the Central Arctic. a Sampling position of sea ice cores (A–E) obtained during three Polarstern expeditions overlaid with the sea ice concentration (June 2014) and a schematic view of the major cold and warm water currents. Blue arrows indicate the inflow of Pacific water. For comparison, previously sampled sea ice cores are included (Ha–Hd); b Total microplastic (MP) particle load m⁻³ of the various sea ice cores (this study) and data reproduced from Fig. 2 of Obbard et al.*; c Average % composition of polymers (polyethylene (PE), varnish (including polyurethanes and polyacrylates), polyamide (PA), ethylene vinyl acetate (EVA), cellulose acetate (CE-Alkylated), polyester (PES) and polypropylene (PP) and others) from the entire core (this study) and digitized data of figure two from Obbard et al.*, acrylic equals varnish (others include acrylonitrile butadiene, chlorinated polyethylene, nitrile rubber, polycaprolactone, polycarbonate, polylactic acid, polyimide, polystyrene, polyvinyl chloride, rubber); d Drift trajectories of sea ice cores, except for land-fast ice station of Greenland (A) and the sample originating from the Chukchi Shelf Ha. The map was created using ArcGIS 10.3 and based on the General Bathymetric Chart of the Oceans (GEBCO)-08 grid, version 20100927, http://www.gebco.net, with permission from the British Oceanographic Data Centre (BODC). *The polymer rayon was excluded

Fig. 2

Images of the microplastic analysis. a Overview image collected by the fourier-transform infrared imaging (FTIR) microscope prior to measurement. b Polymer dependent false-colour image of an exemplary measurement field after FTIR measurement and automated analysis

Fig. 3

Size classes of observed microplastic particles. Box and whiskers plot of percentage (%) shares of MP numbers in different size classes in all sea ice cores. The boundary of the box closest to zero indicates the 25th percentile, the line within the box marks the median and the boundary of the box farthest from zero indicates the 75th percentile. Whiskers (error bars) above and below the box indicate the 90th and 10th percentiles. Blue lines indicate the mean and black circles indicate outliers

Fig. 4

Vertical distribution of ancillary data in sea ice cores. a Refers to the salinity (PSU), b refers to temperature (°C), c refers to particulate organic carbon content (POC; mg×L⁻¹) and d refers to chlorophyll a concentration (µg×L⁻¹) for each core. Steps indicate the sampling horizons taken for each core

Fig. 5

Vertical distribution of microplastic in sea ice cores. a refers to the concentration of microplastic particles (in N×L⁻¹) for each core. b refers to the polymer composition for each core: polyethylene (PE), varnish (including polyurethane and polyacrylate), polyamide (PA), ethylene vinyl acetate (EVA), cellulose acetate (CE-Alkylated), polyester (PES) and polypropylene (PP) and others. c refers to polymer richness (N), and d refers to the Shannon–Wiener index (H'). Steps indicate the sampling horizons taken for each core