A Multi-Tracer Study of Ventilation and Anthropogenic Carbon Storage in the Arctic Ocean

The Arctic Ocean (AO) is a critical sink for anthropogenic carbon (Cant), sequestering emissions via intermediate and deep water formation, storing it for long periods of time. Understanding the timescales of these ventilation processes is essential for calculating the current inventory of Cant as well as predicting the AO’s capacity to store CO2 in a warming climate. However, observational constraints remain limited; while standard transient tracers (SF6, CFC-12) and other radionuclides successfully resolve surface and intermediate layers, they often fail to capture the older waters of the deep basins. Atom Trap Trace Analysis (ATTA) has opened a new way to measure deep ocean water residence times by using the radioactive noble gas 39Ar. Here we show the first fully resolved vertical profiles of Arctic ventilation and Cant using Transit Time Distributions (TTDs) derived from a novel combination of short-lived tracers and long-lived radioisotopes (39Ar, 14C). Their vertical distribution brings key information on ocean ventilation and hence the storage of anthropogenic carbon. We apply a Bayesian Inference framework to fit the TTD parameters from the different tracer data constraints.We find that the mixing regime across the Nansen, Amundsen, and Makarov Basins is more advection-dominated than previously assumed in the deep basins. The profiles reveal that the Arctic stores up to 33% of its total Cant inventory below 1,500 m—vastly exceeding the global ocean average of ∼7%. While the deep Makarov Basin holds roughly half the carbon content of the Eurasian Basin, both reservoirs play a disproportionate role in deep sequestration. Conversely, we demonstrate that for the Atlantic Water Layer, which contains the bulk of the carbon, adding long-lived radioisotopes offers negligible improvement over standard tracers. These findings refine the Arctic carbon budget and highlight the necessity of adding long-lived radionuclides for constraining the deep ocean sink.