Nuclear waste radionuclides unveil three decades of anthropogenic carbon in the Canada Basin of the Arctic Ocean

Ocean-atmosphere CO2 exchange is key in modulating global climate, but the Arctic Ocean’s anthropogenic carbon (Cant) uptake is poorly constrained. Most studies in the Canada Basin using the Transit Time Distribution (TTD) relied on two years of paired gas tracers, CFC-12 and SF6. Here we use nuclear reprocessing products 129I, 236U, and 137Cs to estimate Cant in the Atlantic Water layer by the TTD. We present the evolution of Cant in the Canada Basin from 1993 to 2023, and a high-resolution distribution of Cant across the basin in 2022. We observe a basin-wide inventory increase in the Atlantic Layer (400–1000 m) of 5.5 ± 0.9 Tg C yr−1. Cant content in water entering the Canada Basin tracks increasing atmospheric input, time-lagged by 15-20 years; we anticipate Cant content of up to 65 μmol kg−1 in core Atlantic Water entering the basin by 2050. Nuclear waste tracers reveal three decades of anthropogenic carbon accumulation in the mid-depth Arctic Ocean, with levels tracking atmospheric increases and projected to rise further through 2050.