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

Abstract

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 humidtemperate 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.