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Sedimentary records show that calcium carbonate (CaCO₃) preservation fluctuated during the Eocene. These fluctuations are well documented for the equatorial Pacific. However, data from other basins are sparse. In this study, we report new middle and late Eocene bulk calcium carbonate percentages and accumulation rates from the northwestern Pacific (Ocean Drilling Program—ODP—Site 884) and the Atlantic (ODP Sites 1053, 1090, and 1263) Oceans; in addition, we calculate CaCO₃accumulation rates for sites with published percentage bulk CaCO₃to expand geographic and paleobathymetric coverage. Using these data, we investigate the response of the carbonate cycle to environmental changes (e.g., temperatures, primary productivity, weathering, and ocean circulation) at the beginning of the greenhouse‐icehouse transition (∼43–34 Ma). Our results show that in the middle to late Eocene CaCO₃accumulation rates were highly variable at different paleodepths and ocean basins suggesting that the evolution of carbonate accumulation rates over the Eocene was influenced by different processes in different locations. In particular, our data emphasize the role of surface CaCO₃production and ocean ventilation in driving changes in CaCO₃preservation and burial at the seafloor. Our study also highlights the need for a better understanding of the processes regulating CaCO₃surface production today in order to correctly interpret geological records.

Large volumes of cool water are drawn up to the surface in the tropical oceans. A companion paper shows that the cool water reaches the surface in or near the upwelling zones off northern and southern Africa and Peru. The cool water has a subantarctic origin and spreads extensively across the Atlantic and Pacific basins after it reaches the surface. Here, we look at the spreading in two low‐resolution ocean general circulation models and find that the spreading in the models is much less extensive than observed. The problem seems to be the way the upwelling and the spreading are connected (or not connected) to the ocean's large‐scale overturning. As proposed here, the cool upwelling develops when warm buoyant water in the western tropics is drawn away to become deep water in the North Atlantic. The “drawing away” shoals the tropical thermocline in a way that allows cool subantarctic water to be drawn up to the surface along the eastern margins. The amounts of upwelling produced this way exceed the amounts generated by the winds in the upwelling zones by as much as 4 times. Flow restrictions make it difficult for the warm buoyant water in our models to be drawn away.