| Summary: | Our current understanding of the global meridional overturning circulation (GMOC) is revisited using a surface-forced ocean model simulation constrained by global hydrographic data. The derived GMOC is qualitatively consistent with previous observation-based studies and further provides enhanced spatial details in the sources, transformations, and transports of major global water masses including in poorly observed regions. Several important but relatively underexplored aspects of the GMOC are highlighted, including complex but vigorous heavy-to-light water mass transformation that occurs in the Indo-Pacific and Southern Oceans, and the role of the equatorial Pacific upwelling in closing the GMOC circuit. These and other key aspects of the GMOC are poorly captured in a surface-forced ocean model simulation without the temperature and salinity corrections, suggesting that current climate models do not realistically simulate the GMOC and the associated global heat, salt, and carbon balances.
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