Moving beyond the monolithic Atlantic Multidecadal Variability

The Atlantic is thought to exhibit basin-wide sea surface temperature (SST) variations on decadal timescales, which has been termed the Atlantic Multidecadal Variability (AMV). Historically, the AMV was thought to be the result of ocean dynamics, specifically variations of the Atlantic Meridional Overturning Circulation. However, recent studies have shown that both external forcing and stochastic atmospheric forcing play a substantial role in the AMV. In this presentation, we suggest that progress in understanding mechanisms of Atlantic SST variability has been hampered by the intense focus on basin-averaged SST. We argue that basin averaging obscures understanding because SST variability in the tropics, subtropics, and subpolar gyre differs substantially in terms of the relevant processes, mechanisms, and dominant timescales. As a result of spatial averaging the AMV is due to a mix of processes, and which processes dominate is sensitive to the temporal filtering typically applied when defining the AMV (e.g., the methods of lowpass filtering and removal of the global warming signal). This sensitivity can explain the conflicting claims in the literature regarding the dominant processes leading to the AMV. After describing the pitfalls of the intense focus on the basin-averaged SST, we offer a pathway for moving the field forward.