Spatio-temporal variation of microplastic pollution in the sediment from the Chukchi Sea over five years

Sediment has been considered as an important sink for microplastics (MPs), but there are limited reports about the spatial and temporal variability of MPs in sediment from the Arctic Ocean. Furthermore, understanding is lacking on the correlation between Arctic sea ice variation and MP abundance in sediment. This study aimed to assess the MP contamination in the sediment from the Chukchi Sea over five years through three voyages (in 2016, 2018, and 2020). The MP abundances in the sediments from the Chukchi Plateau and Chukchi Shelf over five years ranged from 33.66 ± 15.08 to 104.54 ± 28.07 items kg^-1 dry weight (DW) and 20.63 ± 6.71 to 55.64 ± 22.61 items kg^-1 DW, respectively. The MP levels from the Chukchi Sea were lower than those from the Eastern Arctic Ocean. Our findings suggest that the Chukchi Plateau is an accumulation zone for fibers related to fishing gear and textiles under the dual influence of the Pacific and Atlantic Ocean currents. However, the reduction of these fibers in the sediment from the Chukchi Shelf might be related to bottom currents, sediment resuspension, and biomass. Moreover, the MP abundance in the sediment from the Chukchi Sea was positively correlated with the reduction of Arctic sea ice, suggesting that the melting sea ice contributes to the increase in MP levels in the sediment. The increase in blue MPs from the Chukchi Plateau over time might be attributed to melting sea ice or intense fishing activity, whereas the increase of the smallest MPs in this region could be owing to the breakdown of larger plastics during long-distance transport or the easier settlement of smaller MPs. Further time-series investigations are urgently required to improve the understanding of the environmental fate and transport of MPs among the different Arctic environmental compartments.