Abstract/Summary

The Atlantic Ocean is ventilated by high-latitude deep-water formation and the associated overturning circulation. An equivalent process is not observed in the Pacific Ocean. This arrangement of the global overturning has dominated for the last 2-3 million years, although older intervals show evidence for different modes of ventilation. In the current climate, the Pacific/Atlantic asymmetry occurs be- cause the Atlantic is more saline, which permits deep convection to penetrate much deeper than in the Pacific. Whether the salinity contrast between the two basins is dominated by atmospheric process (a larger net evaporation over the Atlantic than the Pacific) or oceanic processes (local control of deep convection, salinity transport into the Atlantic) remains an outstanding question. Numerical simulations have provided support for both mechanisms; observations have not delivered a definitive answer. A major avenue for future work is the quantification of the various processes at play to identify which mechanisms are primary.