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 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.
Highlights
Efforts to understand climate response to sustained greenhouse gas forcing commonly focus on periods of peak Cenozoic warmth during the Paleocene–Eocene thermal maximum and early Eocene (e.g., Zachos et al, 2008; Lunt et al, 2012a)
High Polar Amplification under Modest CO2 Forcing These data provide an integrated estimate of the mean climate state for the continental subarctic Giraffe locality over the multimillennial interval common to all proxies
The MCR-inferred paleotemperature and reconstructed CO2 concentrations can be plotted along a range of estimates for the sensitivity of mean annual temperatures (MATs) with respect to atmospheric CO2 (Fig. 4)
Summary
Efforts to understand climate response to sustained greenhouse gas forcing commonly focus on periods of peak Cenozoic warmth during the Paleocene–Eocene thermal maximum and early Eocene (e.g., Zachos et al, 2008; Lunt et al, 2012a). Δ18O from wood cellulose, and foliar stomata from this locality provide a comprehensive reconstruction of late middle Eocene climate and CO2 for the northern subarctic latitudes.
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