• offshore
• Norway
• microplastics
• mesoplastics
• distribution
• deep marine environment
• coastal marine environment
• Arctic
• accumulation
• plastic debris
• sediments

Versatility, stability and low production costs have fuelled global demand for plastic products. As a result of the increase in production, the amount of plastic waste has also increased. Marine plastic debris arises from land disposal, wastewater treatment processes, construction, disposal at sea and the breakdown of in-use plastic item, such as fishing gears. Once at sea plastics can be redistributed by ocean currents and the environmental conditions caused them to be weathered and/or colonised by organisms. These processes lead to a breakdown of plastic items into smaller fragments, changing their properties (more dense, fast sinking rate, etc.) leading them to the seafloor. Therefore, ocean sediments are regarded as the ultimate destination for small plastic particles. Microplastics (<1 mm) besides the degradation of larger plastic items, also include those items which are produced in the micro-size range such as micro-pellets and powers. It is crucial to understand which are the main pattern of distribution to assess which environments could be mainly influenced by the occurrence of plastic debris. This study presents the record of plastic contamination in sediments samples from three different benthic domains, all related to Norwegian waters including the first observation of microplastic contamination in the Kveithola Trough. Three cores were sampled from the Oslofjord, in locations characterised by almost shallow waters (~100 m); two sediment cores were sampled from deep environments (1320 – 1650 m) in the North-eastern slope of the Greenland Sea close to the Svalbard archipelago; and finally, two from Kveithola, a trough engraved on the margin of the shallow Barents Sea bank (230 – 340 m). Plastic particles were detected in every core analysed using a high-density separation approach (NaI, 1.8 g cm-3). Each plastic particle was described based on its morphology (size, shape, colour) under an optical microscope. Further, the polymeric origin of particles was chemically confirmed using Attenuated Total Reflectance – Micro Fourier Transformed Infra-Red Spectrometry (ATR-μFTIR). Grain-size analyses were conducted for sediments with a laser morphometric granulometre. Microplastics (30 μm detection limit – 1000 μm), along with larger plastic debris were identified throughout this study: mesoplastics (1 mm – 10 mm) and macroplastics (1 cm – 5 cm). In total, seven sediment cores (0 – 5 cm) have been investigated using sediment slices of 1 cm each. Results show microplastic deposition in sediment began from 1999 on the Greenland Sea slope and in 1990 in the Kveithola Trough. In the Oslofjord, due to the analysis limit of sediment cores (0-5 cm), ages at the bottom of the cores indicate an accumulation from 1994 and 2002 but it is presumable that microplastics began to settle in the preceding decades. In total, the concentration of plastic particles found in the Oslofjord is of 0.55 MP g-1 d.w. (n= 310), 0.19 MP g-1 d.w. in the Kveithola Trough (n= 13) and 0.05 MP g-1 d.w. in the North-eastern Greenland Sea slope (n= 5). The results show that, except for an area in the Oslofjord, the horizontal distribution of plastic particles is mainly driven by bottom currents, whilst the vertical distribution along the layers in sediment cores is influenced by bioturbation. Based on the morphology of microplastics, it is inferred that the main sources could be fishery activities in Arctic areas, and breakdown of textiles for the more anthropised Oslofjord. Further research is needed to understand the mechanisms influencing transport, accumulation, resuspension and interactions with biota of this form of pollution.