Microplastics (MPs), particles of synthetic plastic less than 5 mm, are a growing global concern, found even in the most remote areas. Previous research has detected MPs in Arctic pack ice, seawater, and seafloor sediments, but the mechanisms behind their distribution and the extent of contamination remain unclear. MPs are expected to eventually settle onto sediments and be buried, but their ingestion by various marine species has been documented, raising concerns about the impact on the marine food web and human health, particularly for indigenous communities that rely heavily on ocean foods. Several processes have been proposed to explain MP transport and accumulation in the Arctic, including the North Atlantic Thermohaline Circulation, wave-driven Stokes drift, riverine input, and sea ice incorporation. Atmospheric transport is also a potential pathway, though poorly understood. The diverse shapes, sizes, colours, and chemical compositions of MPs complicate source identification, with secondary MPs (resulting from the breakdown of larger plastics) being particularly difficult to trace. Fibres are a notable type of MP found in various Arctic samples. Accurate MP identification is hampered by the weathering processes that change their physical and chemical properties over time. Challenges in sampling and analysis also limit our understanding, particularly regarding smaller MPs (<250 µm), which may be more abundant and bioavailable but are difficult to study. This study aims to characterize microplastic abundance, size, and polymer identities throughout the Arctic Ocean, providing insights into their transport, extent, and potential sources to inform mitigation strategies. The focus on subsurface particles and their properties provides valuable information about MP presence, movement, and infra-red profiles in the Arctic.

Existing literature highlights the pervasive nature of microplastic pollution, with studies documenting its presence in various Arctic environments. Early research suggested that processes like the North Atlantic Thermohaline Circulation, Stokes drift, and riverine inputs contribute to MP accumulation in the Arctic. However, the role of atmospheric transport remained unclear. Studies have identified MPs in Arctic sea ice, showing the potential for ice to act as a transport vector. The dominance of fibers in many studies suggests a significant contribution from textile sources. Challenges in identification and quantification of MPs, particularly small particles, are prevalent in the literature. The identification of specific polymer types has been inconsistent across studies, highlighting the need for standardized methods. The study of weathering effects on the spectral properties of MPs is growing, adding another layer of complexity to source identification and transport modeling. Studies about microplastic ingestion by various species of marine life, including those relevant to the Arctic, highlight the ecological implications of plastic pollution. Research on the potential impact of microplastic ingestion on human health, especially for communities relying on seafood, also underlines the urgent need to further investigate this emerging concern.

This study involved collecting seawater samples from 71 stations across the European and North American Arctic during four oceanographic cruises in 2016. Samples were collected at near-surface (3-8 m) depths to avoid bias towards floating plastics and at depths up to 1015 m at six Beaufort Sea sites. Stringent contamination protocols were implemented to minimize contamination during both field and laboratory procedures, including air blanks, procedural blanks, and rigorous cleaning of equipment. Samples were sieved using a 63 µm mesh sieve, and the retained particles were processed for analysis. A two-step analysis was employed: (1) visual microscopy to identify suspected microplastics (SMPs), based on established criteria, and (2) Fourier-transform infrared (FTIR) spectroscopy to confirm the identity of SMPs and determine polymer types. FTIR analysis was performed on a subset of SMPs (37.6%) from each sample. A weighted average calculation was used to estimate the total number of MPs in samples not fully analyzed by FTIR. To address the impact of weathering on spectral properties, a controlled laboratory weathering study of commercial polyester textile samples was conducted over a year. A Peak Ratio Index was developed to quantify the degree of weathering by examining specific peak ratios in the FTIR spectra. Data were analyzed to identify correlations between MP concentrations, size distributions, polymer types, and geographic location. Spatial trends in FTIR peak ratio indices were also mapped to examine variations in weathering across the study area.

The study documented the widespread presence of MPs in Arctic seawater, with average counts of 186 ± 15.4 suspected microplastics (SMPs) per cubic meter. FTIR analysis confirmed that 40.5 ± 4.4 particles per cubic meter were microplastics. Fibres constituted the majority (92.3%) of the particles, with polyester making up 73.3% of the synthetic fibres. A significant correlation between MP concentration and longitude was observed, with significantly higher concentrations in the Atlantic-influenced eastern Arctic compared to the Pacific-influenced western Arctic. While fibre length did not vary significantly with longitude, the length of SMPs did. FTIR analysis revealed an east-to-west gradient in the infrared signatures of polyester fibres, suggesting weathering of fibres as they move westward. The Peak Ratio Index showed a significant relationship with longitude, indicating higher weathering in the western Arctic. MPs were found throughout the water column in the Beaufort Sea, with polyester being the dominant polymer at all depths. The concentration of MPs varied with depth, potentially related to water mass properties, although further research is needed to confirm this. The findings suggest that a substantial amount of relatively fresh polyester fibers enter the Arctic Ocean via Atlantic inputs and/or atmospheric transport from the south. The high prevalence of polyester fibers highlights the potential contribution of textiles and wastewater discharges to global microplastic pollution, even reaching the remote Arctic.

The findings of this study strongly suggest that the Atlantic Ocean is a major source of microplastic fibres in the Arctic, primarily polyester fibres originating from textile sources. The observed east-west gradient in the degree of weathering of polyester fibers further supports this conclusion. The high prevalence of polyester fibres underscores the significant impact of textile-related waste and wastewater discharge on global microplastic pollution, emphasizing the need for interventions to mitigate this form of pollution. The study confirms the widespread presence of microplastics even in the remote Arctic, highlighting the global reach of this pollution. The observed variations in MP concentrations and weathering levels may also suggest additional factors influencing the distribution, such as atmospheric transport and local sinking patterns. Further research is needed to refine our understanding of these processes.

This study provides compelling evidence of the pervasive distribution of microplastics, particularly polyester fibres, in the Arctic Ocean. The findings suggest that Atlantic Ocean currents are a major pathway for their transport into this remote region. The dominance of polyester fibres highlights the significant role of textiles and wastewater discharges in global microplastic pollution. The study underscores the need for further research to fully understand the processes involved in the transport, fate, and impacts of microplastics in the Arctic, along with mitigation strategies focusing on reducing sources of microplastic pollution.

The study's reliance on a 63 µm mesh size may have resulted in underestimation of smaller MPs. The visual identification of suspected MPs, even with FTIR confirmation for a subset of samples, introduces potential for some level of subjectivity and error. While a controlled weathering study was conducted, the complexity of weathering processes in the natural environment means that the observed spectral changes in the laboratory might not fully represent the weathering changes in the Arctic Ocean. The study's focus on near-surface and specific depth profiles in the Beaufort Sea limits the generalizability of the findings to the entire Arctic Ocean. More extensive sampling and 3-D numerical modeling are needed to fully understand the complex interplay of factors that affect the distribution of microplastics in the Arctic Ocean.