Near-inertial waves (NIWs), typically generated by surface wind forcings, propagate into the ocean interior and contribute to vertical mixing and energy redistribution. Although NIW activity in the Arctic Ocean is generally weaker than in other basins, it may evolve under ongoing sea ice decline and increasing winter storms. Here, we present the direct observations of deep NIW activity from long-term near-bottom current measurements at six sites in the western Arctic Ocean. The observations reveal clear spatial and temporal variability. Spatial differences in deep NIW activity are primarily controlled by variations in near-bottom stratification structure, which modulate the vertical decay of NIW energy. Temporally, NIW energy exhibits a pronounced seasonal cycle, with stronger energy in July–January than in January–June, more closely related with sea ice kinetic energy than sea ice concentration alone, which reveals the role of ice mobility. Ice age also appears to modulate NIW generation: thinner first-year ice is more easily displaced by wind, facilitating momentum transfer to the ocean and intensifying NIW generation. However, NIW energy was anomalously strong during the winter of 2021–2022 despite extensive multi-year ice coverage, likely because rough subsurface of multi-year ice increased momentum transfer despite its reduced mobility. These results provide new insights into the variability and structure of deep NIWs in the Arctic Ocean.

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