Subpolar North Atlantic Ocean heat content drives 21st-century Arctic multi-decadal variability in CESM1 LE

Arctic surface temperatures exhibit a pronounced multi-decadal oscillation superimposed on the long-term anthropogenic warming trend, yet its drivers remain poorly understood. Here we identify a critical oceanic mechanism originating in the subpolar North Atlantic. We show that variability in upper-layer (0-200 m) ocean heat content in this region precedes fluctuations in poleward ocean heat transport convergence (OHT) by approximately five years, which subsequently lead Arctic surface temperature changes by two years. Using a time-evolving radiative kernel method and PCMCI causal analysis within the Community Earth System Model Large Ensemble, we quantify the contributions to this variability. OHT directly accounts for 44.5% of Arctic temperature variability, while local feedbacks (principally albedo and lapse rate) amplify this signal, contributing an additional 53.5%. These findings underscore that this sequential oceanic process, originating in the subpolar North Atlantic and propagating into the Arctic, is critical in modulating the phase of Arctic multi-decadal temperature variability. Understanding this sequential mechanism could enhance decadal to multi-decadal climate predictions and future projections.