Reconstructing Devonian palaeoatmosphere & palaeoecology using fossil plant traits

Abstract

This thesis examines the reconstruction of atmospheric CO2 concentration during the Devonian period and the palaeoecology of Ireland's first fossil forests at the Devonian/Carboniferous boundary. The expansion and diversification of terrestrial plant life during the Devonian period is thought to have had significant consequences for atmospheric CO2 concentrations via enhanced weathering processes. However, there is a paucity of existing CO2 proxy data for this period. The advent of mechanistic gas exchange proxies in recent years has provided an opportunity to better constrain changes in atmospheric CO2. Paired stomatal measurements and carbon isotopic data from Sawdonia plant fossils were used to parameterise the gas-exchange-based model of Franks et al. (2014) to reconstruct atmospheric CO2 concentrations for the Emsian stage of the Devonian (Chapter 2). The results of this chapter indicate atmospheric CO2 concentrations were approximately 898 ppm (+616/-405 ppm) prior to the emergence of forest ecosystems. A sensitivity analysis of input parameters for the model was used to inform revisions to existing estimates using the same model. The thesis goes on to investigate the leaf morphological diversity and leaf allometry of Archaeopteris hibernica in one of Ireland's first fossil forest ecosystem (Chapter 3). Chapter 4 considers the physiological and ecological functioning of Archaeopteris hibernica using established methods to estimate the fossil plant functional traits of leaf mass per area and maximum stomatal conductance. The leaf trait analysis of A. hibernica was found to indicate that A. hibernica had a high leaf mass investment per unit area and a probable stress-tolerant ecological strategy. Finally, future directions for research and the limitations of this study are discussed in Chapter 5. The findings of this thesis highlights the need to further clarify the atmospheric and environmental context and physiological functioning of the first forest ecosystems to understand the evolution of plant-climate and plant-atmosphere interactions.