Late Eocene tropical sea surface temperatures: A perspective from Panama

We have reconstructed mean annual coastal temperatures and seasonality during the Eocene (Priabonian; 36.6–40 Ma) using oxygen isotope profiles of shallow marine aragonitic gastropod shells (Gatuncillo Formation, Panama). These data provide a unique opportunity to document low‐latitude coastal climates during a preglacial “greenhouse” period. Assuming shell oxygen isotope profiles primarily reflect changes in water temperature, our results indicate water temperatures in a middle to outer shelf setting (20–50 m depth) varied by 6°–8°C, and mean annual temperatures (MAT) were >26°C. These temperatures are in agreement with pollen‐based surface temperature reconstructions for the late Eocene and are consistent with other Eocene mollusk‐based tropical coastal temperature estimates but are at odds with the few Eocene foraminiferal‐based estimates of mean annual tropical sea surface temperatures (∼17°–22°C).