Nuclear Waste Unveils Three Decades of Anthropogenic Carbon in the Canada Basin of the Arctic Ocean

Ocean-atmosphere CO2 exchange plays a key role in modulating global climate, but the Arctic Ocean’s anthropogenic carbon (C _{ant ) uptake is still poorly constrained. Studies of C ant in the Arctic Ocean are limited by their dependence on indirect methods and data availability. Here, we use the anthropogenic nuclear reprocessing products ^{129 I, 236 U, and 137 Cs to estimate C ant in the Atlantic Water layer in the Canada Basin by the Transit Time Distribution (TTD) method. Until recently, all studies in the Canada Basin using the TTD method relied on just two years of paired gas-tracer (CFC-12 and SF 6 ) data or a few years of single-tracer data, and spatial coverage of paired tracers was limited to the western boundary of the basin. We present the first decadal and sub-decadal study of C ant in the Canada Basin, spanning 1993 to 2023, and the first high-resolution study of C ant distribution across the entire basin, conducted in 2022. We report an increasing rate of C ant concentration of 0.76 μmol/kg/yr as it enters the Canada Basin in the core Atlantic Water transported by the Arctic Ocean Boundary Current. All three measured radionuclide tracer concentrations indicate minimal dilution in the core of AW when compared to input concentrations in the Eurasian Basin, and we suggest this also applies to C ant transported to the Canada Basin. As C ant concentrations in water entering the Canada Basin continue to follow increasing atmospheric inputs of CO 2 , time-lagged by approximately 15-20 years, we anticipate concentrations of up to 65 μmol/kg by 2050 in the Atlantic Water layer of the Canada Basin.}}