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Surface buoyancy fluxes in the Southern and North Atlantic Oceans are presumed to disproportionately influence the ocean's residual global overturning circulation (GOC) with respect to those in the Indo-Pacific. Here, this assumption is challenged through an assessment of global buoyancy transport in the Community Earth System Model 1.0, which reveals that the steady state GOC is equally constrained by surface buoyancy flux everywhere. Further, an unacknowledged aspect of the GOC is demonstrated: it transports buoyancy from where it is gained at the surface, predominately in the Indo-Pacific, to where it is lost, predominately in the Atlantic and Southern Oceans. This global buoyancy transport requires zonal structure in the GOC, linking the Atlantic and Indo-Pacific within the Southern Ocean, asymmetry and interbasin coupling absent from many conceptual descriptions of overturning dynamics. These results compel a more nuanced appreciation for an Indo-Pacific influence in GOC evolution.

Plain Language Summary The great conveyor belt of global currents that transit the global oceanthe global overturning circulationcarry with them heat, freshwater, and dissolved gases that are essential to Earth's climate. Changes in heating and cooling of the ocean surface, or changes to patterns of precipitation, are known to influence this global-scale circulation, but a full understanding of the response remains incomplete. In this study, we develop a new technique to study the global overturning circulation. Our methods use the spatial patterns of ocean surface processes, for example, heating and cooling, precipitation and evaporation, to infer circulation behaviors deep in the ocean's interior. Historically, deep ocean behaviors were thought to be influenced by surface processes occurring at the high latitudes. Here, using this new technique, we find that surface processes at the low latitudes of the Indo-Pacific Oceans are equally essential in determining the strength and structure of the global overturning circulation. As a consequence, the climate that we experience at Earth's surface may depend far more heavily on the processes occurring at the equatorial Indo-Pacific Ocean surface than often assumed.