Reconstruction of atmospheric CO 2 during the early middle Eocene by application of a gas exchange model to fossil plants from the Messel Formation, Germany

Abstract

In this study, atmospheric CO 2 during the early middle Eocene (~ 47 Ma) is reconstructed using fossil plants from the Messel Formation close to Darmstadt, Germany. CO 2 concentration is calculated using a mechanistic model of gas exchange which optimizes CO 2 uptake by photosynthesis against water vapor loss by transpiration, a strategy that is commonly realized in land plants. Input data for the model are stomatal data (density and pore length), paleoclimate data obtained by two different approaches and biochemical parameters of photosynthesis. Leaves from three taxa belonging to two different families were studied: Laurophyllum lanigeroides, Daphnogene crebrigranosa (both Lauraceae) and Rhodomyrtophyllum sinuatum (Myrtaceae). The results suggest that CO 2 was between 853 and 1033 ppm during the development of the Messel Formation. Stomatal data therefore indicate a CO 2 concentration that was substantially higher than today. The reconstructed range of CO 2 concentration is close to data provided by geochemical modeling results and conforms to various data that indicate a warm and ice-free climate during this time interval.