Middle Eocene CO2and climate reconstructed from the sediment fill of a subarctic kimberlite maar

Eocene paleoclimate reconstructions are rarely accompanied by parallel estimates of CO 2 from the same locality, complicating assessment of the equilibrium climate response to elevated CO 2 . We reconstruct temperature, precipitation, and CO 2 from latest middle Eocene (ca. 38 Ma) terrestrial sediments in the posteruptive sediment fill of the Giraffe kimberlite in subarctic Canada. Mutual climatic range and oxygen isotope analyses of botanical fossils reveal a humid-temperate forest ecosystem with mean annual temperatures (MATs) more than 17 °C warmer than present and mean annual precipitation ∼4× present. Metasequoia stomatal indices and gas-exchange modeling produce median CO 2 concentrations of ∼630 and ∼430 ppm, respectively, with a combined median estimate of ∼490 ppm. Reconstructed MATs are more than 6 °C warmer than those produced by Eocene climate models forced at 560 ppm CO 2 . Estimates of regional climate sensitivity, expressed as ∆MAT per CO 2 doubling above preindustrial levels, converge on a value of ∼13 °C, underscoring the capacity for exceptional polar amplification of warming and hydrological intensification under modest CO 2 concentrations once both fast and slow feedbacks become expressed.