North Atlantic CO2 sink variability revealed by the Go-Ship A25-OVIDE section

About 30% of the carbon dioxide derived from human activities (C_ANTH) has been absorbed by the ocean (DeVries, 2014; Gruber et al., 2019; Friedlingstein et al., 2021), with the North Atlantic (NA) being one of the largest C_ANTH sinks per unit area (Khatiwala et al., 2013; Sabine et al., 2004). In the NA, oceanic C_ANTH uptake strongly relies on the meridional overturning circulation and the associated regional winter deep convection. In fact, the formation and deep spreading of Labrador Sea Water stands as a critical C_ANTH gateway to intermediate and abyssal depths. The NA C_ANTH uptake has fluctuated over the years according to changes in the North Atlantic Oscillation. Biennial observation of the marine carbonate system along the Go-Ship A25-OVIDE section has allowed us assessing the decadal and interannual variability of the C_ANTH storage in the subpolar NA from 2002 to 2021. In this study, we investigate 1) the trend of C_ANTH and 2) the relationship between the C_ANTH saturation, the apparent oxygen utilization, and the ventilation of the water masses between the A25-OVIDE section and the Greenland-Iceland-Scotland sills during 2002-2021. We divided the A25-OVIDE section into three main basins (Irminger, Iceland, and Eastern NA). Our results show that the Irminger Basin presents a more homogenous C_ANTH profile and higher C_ANTH saturation values at depth than the other two basins, which is related to the pronounced convective activity in the Irminger Basin. In contrast, the Eastern NA Basin has higher C_ANTH values at the surface due to its higher surface temperature, but its deep water masses show the lowest C_ANTH values since they are the less ventilated in the section. Our analysis also reveals that, overall, the NA C_ANTH storage has increased during 2002-2021, but varied according to the ventilation changes. While the Eastern NA water masses experienced a relatively constant, although shallower, average ventilation, the Irminger and Iceland Basins underwent a less steady C_ANTH uptake pattern characterized by alternating periods of strong and weak C_ANTH storage.