The classic paleotemperature record based on δ18O data from pelagic foraminiferal calcite suggests that equatorial sea-surface temperatures during the Maastrichtian (∼12–20 °C) were much cooler than today (∼27–29 °C). Such cool equatorial temperatures contradict basic theories of tropical atmospheric and ocean dynamics. We report δ18O data from remarkably well preserved rudist aragonite and magnesian calcite cements of Maastrichtian age (∼ 69 ± 1 Ma) from the carbonate platform of Wodejebato guyot in the western Pacific. These data suggest that equatorial sea-surface temperatures in the Maastrichtian (best estimate ∼ 27–32 °C) were at least as warm as today. This finding helps reconcile the geologic δ18O record with ocean-atmospheric dynamic theory and implies a reduction in the poleward heat flux required by global climate simulations of greenhouse conditions.

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