Anthropogenic carbon pathways towards the North Atlantic interior revealed by Argo-O₂, neural networks and back-calculations

The subpolar North Atlantic (SPNA) is a region of high anthropogenic CO2 (C-ant) storage per unit area. Although the average Cant distribution is well documented in this region, the C-ant pathways towards the ocean interior remain largely unresolved. We used observations from three Argo-O-2 floats spanning 2013-2018 within the SPNA, combined with existing neural networks and back-calculations, to determine the C-ant evolution along the float pathways from a quasilagrangian perspective. Our results show that C-ant follows a stepwise deepening along its way through the SPNA. The upper subtropical waters have a stratified C-ant distribution that homogenizes within the winter mixed layer by Subpolar Mode Water formation in the Iceland Basin. In the Irminger and Labrador Basins, the high-Cant footprint (> 55 mu mol kg(-1)) is mixed down to 1400 and 1800 dbar, respectively, by deep winter convection. As a result, the maximum C-ant concentration is diluted (<45 mu mol kg(-1)). Our study highlights the role of water mass transformation as a first-order mechanism for C-ant penetration into the ocean. It also demonstrates the potential of Argo-O-2 observations, combined with existing methods, to obtain reliable C(ant)t estimates, opening ways to study the oceanic C-ant content at high spatio-temporal resolution.