A Southern Ocean Multidecadal Oscillator Forced by Deep Convection

Abstract Some climate models exhibit multidecadal‐to‐centennial variability of the Southern Ocean (SO) associated with open‐ocean polynyas and deep convection. We characterize the SO variability of the Community Earth System Model (version 1) under preindustrial conditions run with two different ocean resolutions, low‐resolution (∼1°) and high‐resolution (∼0.1°). Only the high‐resolution configuration produces multidecadal oscillations in the SO, and we find two patterns of sea surface temperature and salinity that describe the variability as a coupled oscillator. Previously, coupled atmosphere–ocean feedbacks have been proposed to explain the oscillations, but we find little evidence that atmospheric variability is necessary. Instead, we propose that deep convection triggers a shift in the SO circulation, which changes the salinity of waters upwelled then advected over the Maud Rise, where the deep convection occurs.