Northern North Atlantic climate variability controls on ocean carbon sinks in EC-Earth3-CC

Abstract. The northern North Atlantic is an important net sink of atmospheric CO₂, though air-sea CO₂ fluxes exhibit substantial variability across different timescales. The underlying drivers of this variability remain poorly understood across both temporal and regional scales. Here, we investigate interannual to decadal CO₂ flux variability in the northern North Atlantic using historical simulations from the EC-Earth3-CC model. We assess the role of key dynamical and physical processes in shaping CO₂ flux variability across five regions: the Nordic Seas, eastern Nordic Seas, the eastern and western subpolar North Atlantic, and the full North Atlantic. Our analysis reveals that physical parameters—including sea ice concentration (SIC), sea surface temperature (SST), sea surface salinity (SSS), and wind stress—along with dynamical processes related to ocean mixing and circulation, play a central role in regulating CO₂ flux variability. Using regression analysis, we demonstrate that these drivers exert regionally and temporally varying influences, with our models achieving high R² values indicating a strong degree of explanation for CO₂ flux variability. The regression models capture interannual variability more effectively than decadal variability, highlighting the dominant role of short-term fluctuations in shaping CO₂ flux dynamics. Overall, our results demonstrate that the predictors of CO₂ flux variability are both spatially and temporally dependent. We find that CO₂ flux variability cannot be fully explained by simple linear correlations with individual predictors but instead arises from complex interactions among multiple physical and dynamical processes. Notably, CO₂ flux variability is particularly sensitive to changes in certain predictors, such as wind stress, consistent with expectations based on the gas transfer equation used to compute air-sea CO₂ fluxes.