Black carbon (BC) aerosols play important roles in Arctic climate change, yet they are not well understood because of limited observational data. We observed BC mass concentrations (m_BC) in the western Arctic Ocean during summer and early autumn 2016–2020. The mean m_BC in 2019 was much higher than in other years. Biomass burning was likely the dominant BC source. Boreal fire BC transport occurring near the surface and/or in the mid-troposphere contributed to high-BC events in the Arctic Ocean.