Temporal evolution of anthropogenic carbon in the Irminger Sea between 2011–2021: from accumulation to stabilization

Abstract. The ocean mitigates anthropogenic climate change by absorbing roughly a quarter of anthropogenic CO₂ (C_ant), at the cost of ongoing ocean acidification, threatening marine life. The North Atlantic Ocean exhibits the highest ocean storage capacity of C_ant per unit area. The subpolar North Atlantic is subject to a large seasonal to decadal variability that might impact this C_ant storage. Here, we investigate the monthly C_ant evolution over 2011–2021 and its relationship with regional ocean dynamics. We combined Argo-O₂ observations, neural networks, and the back-calculation φC_T^O method to derive a monthly time series of C_ant inventory in the Irminger Sea. In the top 2000 dbar, C_ant inventories increased at a rate of 0.96±0.18 mol m^-2 yr^-1 (1.28±0.24 % yr^-1) over 2011–2021. However, this increase was not consistent over time, with no net increase observed between 2016 and 2021. Over 2016–2021, when Deep-Argo data became available, the C_ant inventory below 2000 dbar increased by 0.53±0.12 mol m^-2 yr^-1 but depicted a transition from positive to negative accumulation rates around mid- 2019. The monthly resolution of Argo-O₂ data reveals that the largest changes in C_ant occur during winter. It underscores the importance of wintertime processes such as deep convection that are not captured by summer cruises. This enhanced temporal resolution also enables robust detection of shifts in storage rates. This study highlights the ability of Argo-O₂ data to resolve interannual to decadal C_ant variability, complementing the interpretation ship-based measurements, which are more accurate but temporally sparse.