| Summary: | 2018 Ocean Sciences Meeting, 11-16 February, in Portland, Oregon Many climate models show strong variability in preindustrial Southern Ocean (SO) sea surface temperatures (as well as heat fluxes, sea-ice, salinity, and mixed layer depths) associated with open-ocean deep convection through polynyas. The CM2MC model, a coarse-resolution 3° version of GFDL’s ESM2M model, demonstrates regular multi-decadal variability of SO open-sea convection in a 5000-year-long control simulation. Under climate-driven freshening of the surface Southern Ocean, polynya-mediated convection shuts down. We explore the mechanisms for regular SO convection—and its climate-driven shutdown—by analyzing results from 3-member ensembles of a long control simulation, historical and RCP8.5 scenarios up to the year 2100, a SO wind increase experiment, and a SO freshwater hosing experiment. We hypothesize that this regular SO variability is primarily driven by a shallow preconditioning mechanism, where near-surface density anomalies induce destratification of the water column at the site of polynya formation. We also explore a simple 2 layer and sea-ice column model to understand this convective oscillation. We hypothesize that a delicate equilibrium between warming from CDW, cooling from the atmosphere, and freshening from ice dynamics can explain the emerging time-scales of internal oscillation in the system. SO water mass formation is significantly impacted by variability in convection. We propose that Antarctic Bottom Water (AABW) formation and the Antarctic Circumpolar Current (ACC) increase in decades with strong convection, while Antarctic Intermediate Water (AAIW) decreases. An analysis of the oceanic implications of a permanent shutdown of convection with climate warming (and under freshwater hosing) shows AABW formation drastically decreasing, along with complex behavior of the intermediate and mode waters. The AABW and AAIW also serve as teleconnections pathways for northward propagation of temperature and salinity anomaly signals, ...
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