Presenter: Anton Velo (CSIC)

Description:
Despite covering only 15% of the global oceanic area, the North Atlantic (NA) accumulates one of the highest contents of anthropogenic CO₂ (C_ANTH) in the ocean, storing 23% of the oceanic C_ANTH (Sabine et al., 2004). In terms of C_ANTH increase, large regions of the NA recorded average rates of 1.2 ± 0.1 mol m^-2 yr^-1 during 1994-2007, doubling the global oceanic rate of C_ANTH increase of 0.65 ± 0.08 mol m^-2 yr^-1 (Gruber et al., 2019). In the NA, high C_ANTH concentrations penetrate to mid and abyssal depths as a result of the formation and deep spreading of Labrador Sea Water. These processes are linked to the meridional overturning circulation and winter convection occurring in the NA subpolar gyre. Differences in C_ANTH storage rates have been observed between different phases of the NA Oscillation (NAO), attributed to both changes in C_ANTH concentration and decreases in volumetric water mass census (Fröb et al., 2018). There has been a 50% slowdown in the rate of C_ANTH increase in the NA subpolar gyre between 1994 and 2007, coinciding with a period of low NAO. Biennial observation of the marine carbonate system along the GOSHIP A25-OVIDE section has allowed assessing the long-term and interannual variability of the C_ANTH storage in the subpolar NA from 2002 to 2018. In this research, we determined the increases of C_ANTH in the water masses present between the OVIDE section and the Nordic sills. The average accumulation rate C_ANTH in the water column between the A25-OVIDE section and the sills was 0.90 ± 0.08 mol m^-2 yr^-1 (0.041 ± 0.003 Pg-C yr^-1) for 2002-2021, being 61% higher than the 0.54 ± 0.06 mol m^-2 yr^-1 observed for 1997-2006 (low NAO). The increase in the C_ANTH accumulation rate during 2002-2021 is mainly found in the Irminger and Iceland basins and is mainly associated with the period of high NAO that occurred after 2014. In these two basins, the C_ANTH accumulation rates during the high NAO double those found during the low NAO.