A MIDDLE EOCENE (~45 MA) ATMOSPHERIC CO2 RECONSTRUCTION FROM FOSSIL METASEQUOIA, AXEL HEIBERG ISLAND (NUNAVUT, CANADA)

The Eocene (55-34 Ma) has been well studied by paleoclimatalogists largely because of the dramatic climate shift from the early Eocene global greenhouse to the onset of Antarctic glaciation at the Eocene-Oligocene boundary. Paleoatmospheric CO₂ studies have focused primarily on the early Eocene Climatic Optimum (EECO) (~52 Ma), which saw peak Cenozoic warmth, and the middle Eocene Climate Transition (MECT) (~42-38 Ma). Relatively little work has been done to reconstruct atmospheric CO₂ from the middle Eocene, before the MECT began and after the EECO peak warmth, and the few estimates available fail to reach any reasonable consensus. The buried arctic forests of Axel Heiberg, Nunavut, Canada, have been dated to 45 Ma and provide extremely well preserved fossil Metasequoia. Previously, the Metasequoia from Axel Heiberg proved too fragile for use in paleoatmospheric CO₂ reconstructions based on stomatal methods that require isolating cuticle. We present a new, simplified, method for obtaining clear Metasequoia cuticle from Axel Heiberg using hydrofluoric acid and epiflouresence microscopy. We also present an initial, high-resolution CO₂ record derived from 25 leaf-litter horizons. We test two approaches for reconstructing CO₂ from stomatal geometry: the traditional approach of calibrating to extant Metasequoia and a new, gas exchange based approach.