The Limited Influence of the NAO on Atlantic Multidecadal Climate Variability through Changes in Ocean Circulation

Observed low-frequency fluctuations in North Atlantic sea-surface temperatures (SST) are associated with significant climate impacts over North America, Europe, and throughout the tropics. Most proposed mechanisms for this variability typically require the interaction between multi-year surface heat flux (SHF) anomalies and coherent changes in the large-scale ocean circulation. However, recent modeling work posits that ocean dynamics has a limited influence on Atlantic Multidecadal Variability. This work finds that in CESM SHF anomalies associated with the North Atlantic Oscillation (NAO) produce a lagged SST response when interactive ocean dynamics are included, consistent with previous studies; however, associated SST anomalies are small and the influence is limited to the sub-polar gyre. Further, the magnitude of the lagged response to NAO forcing is non-linear in this model. Finally, we show that the NAO is similar for varying levels of ocean model complexity. While CESM produces an ocean circulation response to the NAO, preliminary analysis demonstrates that other models exhibit responses of different magnitudes or do not simulate responses. Overall, interactive ocean circulation has limited influence on variations in the North Atlantic SST and does not appear to have a large enough influence to feed back onto the NAO or many of the associated climate impacts.