Energetics of the Southern Ocean Mode.

Recently, multidecadal variability in the Southern Ocean has been found in a strongly eddying global ocean circulation model. In this paper, we study the Lorenz energy cycle of this so‐called Southern Ocean Mode (SOM). The Lorenz energy cycle analysis provides details on the energy pathways associated with the SOM. It shows that ocean eddies and the baroclinic energy pathway together with variations in the kinetic energy input by the wind are crucial aspects of the variability. It is also shown how convective mixing, which is induced by the SOM in particular in the Weddell Gyre, is responsible for the large‐scale multidecadal variability in Antarctic Bottom Water and Atlantic Meridional Overturning Circulation. Plain Language Summary: Recently, large fluctuations of the oceanic heat content were discovered in the Atlantic sector of the Southern Ocean in an ocean simulation. These changes are periodic and repeat every 50 years, which is why we cannot confirm them from out limited observational record. We investigate this phenomenon through a mechanical energy perspective and find that it is likely caused by an interplay between eddies (the oceanic equivalent of atmospheric storms with 10‐ to 100‐km diameter) and the average flow around Antarctica. In addition, we find connected sinking events that influence the ocean's overturning strength. If this phenomenon is found in the real ocean, it may influence the global mean surface temperature significantly over decades. Key Points: The multidecadal varying Lorenz energy cycle of a global ocean model is analyzedA mechanical energy description of the Southern Ocean Mode is providedA detailed physical mechanism for the Southern Ocean Mode is proposed [ABSTRACT FROM AUTHOR]