Spatial patterns, environmental correlates, and potential seasonal migration triangle of polar cod (Boreogadus saida) distribution in the Chukchi and Beaufort seas

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.

The impact of rising sea temperatures on an Arctic top predator, the narwhal

Arctic top predators are expected to be impacted by increasing temperatures associated with climate change, but the relationship between increasing sea temperatures and population dynamics of Arctic cetaceans remains largely unexplored. Narwhals (Monodon monoceros) are considered to be among the most sensitive of Arctic endemic marine mammals to climate change due to their limited prey selection, strict migratory patterns and high site fidelity. In the context of climate change, we assume that the population dynamics of narwhals are partly influenced by changes in environmental conditions, with warm areas of increasing sea temperatures having lower abundance of narwhals. Using a unique large dataset of 144 satellite tracked narwhals, sea surface temperature (SST) data spanning 25 years (1993–2018) and narwhal abundance estimates from 17 localities, we (1) assessed the thermal exposure of this species, (2) investigated the SST trends at the summer foraging grounds, and (3) assessed the relationship between SST and abundance of narwhals. We showed a sharp SST increase in Northwest, Mideast and Southeast Greenland, whereas no change could be detected in the Canadian Arctic Archipelago (CAA) and in the Greenland Sea. The rising sea temperatures were correlated with the smallest narwhal abundance observed in the Mideast and Southeast Greenland (< 2000 individuals), where the mean summer sea temperatures were the highest (6.3 °C) compared to the cold waters of the CAA (0.7 °C) that were associated with the largest narwhal populations (> 40,000 individuals). These results support the hypothesis that warming ocean waters will restrict the habitat range of the narwhal, further suggesting that narwhals from Mideast and Southeast Greenland may be under pressure to abandon their traditional habitats due to ocean warming, and consequently either migrate further North or locally go extinct.