CONSENSUS AROUND A COMMON DEFINITION OF ATLANTIC OVERTURNING WILL PROMOTE PROGRESS

Abstract

Quantifying the strength of the Atlantic Meridional Overturning Circulation (AMOC) involves separating the north-ward and southward limbs and calculating their volume transports. The limbs can be distinguished either by depth level or by density class, but recent results have indicated that this choice of coordinate system leads to divergent results, both in terms of the AMOC mean state and its variability. Here, we demonstrate that the AMOC in density coordinates is more informative of the large-scale, three-dimensional AMOC structure, is more closely aligned with the AMOC’s climatic impact via oceanic meridional heat trans-port, and retains more information about future AMOC pathways than the depth space definition. Adopting a commonly accepted definition of the AMOC in density coordinates will unify a divided literature and promote progress in the field. This commentary thus highlights that the coordinate system used to define the AMOC matters, not only for understanding physical processes and past variations that remain elusive, but also for physically appropriate monitoring of its future evolution.