The ocean plays a major role in the moderation of anthropogenically-induced climate change by absorbing roughly a quarter of anthropogenic CO2 (Cant). This absorption of Cant by the ocean leads to ocean acidification, threatening marine’s life. The North Atlantic Ocean encompasses the highest ocean storage capacity of Cant per unit area. The subpolar North Atlantic gyre is subject to a large seasonal to decadal variability that might impact Cant storage. To investigate Cant evolution over the 2011-2021 period and its relationship with ocean dynamics in this region, we use the Argo-O2 array combined with neural networks and a back-calculation method (φCTO method). We compute monthly time-series of Cant in the Labrador and Irminger Seas. We show that Cant concentrations in the first 2000 dbar of the Labrador and Irminger Seas are strongly affected by winter deep convection, especially between winter 2015 and winter 2018. The Cant inventories in the top 2000 dbar of the Labrador and Irminger Seas increase through time, at rates of 1.63±0.32% yr-1 and 1.49±0.30% yr-1, respectively. Our monthly Argo-based Cant estimates complement high-quality ship-based measurements acquired at a biennial or lower frequency. Additionally, this study shows that Cant concentrations and Cant inventories in deep convection areas may depend on the method employed to calculate Cant. As a consequence, we take over the model ensemble idea and propose to use several methods to compute Cant, which would give its methodological uncertainty.

The Reykjanes Ridge is a major topographic feature that lies south of Iceland in the North- Atlantic Ocean and strongly influences the Subpolar Gyre (SPG) circulation. Based on velocity and hydrographic measurements carried out along the crest of the Ridge from the Icelandic continental shelf to 50°N during the RREX cruise in June-July 2015, we derived the first direct estimates of volume and water masses transports over the Ridge. The circulation was mainly westward north of 53.35°N and eastward south of it. The westward transport was estimated at 21.9 ± 2.5 Sv (Sv = 10 6 m 3 s -1 ) and represents the SPG intensity. The westward flows followed two main pathways at 57°N near Bight Fracture Zone and at 59 – 62°N. We argue that those pathways were respectively connected to the northern branch of the North Atlantic Current and to the Sub-Arctic Front that were intersected by the southern part of the section. In addition to this horizontal circulation, mixing and bathymetry shaped the water mass distribution. Water mass transformations in the Iceland Basin lead to the formation of weakly stratified SubPolar Mode Water (SPMW). We explain why SPMW, which was the main contributor in terms of water mass to the westward flow, was denser at 57°N than at 59–62°N along the Ridge. At higher densities, both Intermediate Water, defined by a dissolved oxygen minimum, and Icelandic Slope Water contributed as much to the westward transport across the Ridge as the sum of Labrador Sea Water and Iceland-Scotland Overflow Water.