Environmental Change and Biotic Impacts of a Transient Greenhouse Warming Event in the Middle Eocene

SUMMARY Global atmospheric carbon dioxide levels (pCO2) are rising at a rate unprecedented in Earth's history as a result of human activity. Current atmospheric pCO2 is 387 ppmv and exceeds concentrations reported for the last ~25 million years of Earth's history. To predict the future response of the Earth's system to increasing pCO2 it is imperative that we develop a better understanding of how global climate and carbon cycling has varied during high pCO2 time intervals in the past. A good analogue is the Eocene Epoch (55-34 million years ago, Myr) because it is the most geologically recent interval of sustained global warmth characterised by high pCO2 (> 1000 ppm). The research proposed focuses on a recently discovered, short-lived global warming event during the middle Eocene approximately 40 million years ago - the Middle Eocene Climatic Optimum (MECO). During this event, global temperatures rose by 4 to 6 degrees celsius and the deep ocean became more acidic, presumably as a consequence of a temporary increase in atmospheric pCO2. This event is particularly interesting because the timing and cause of the MECO differ from other warming events reported in the Eocene. However, we know very little about the environmental changes that accompanied this unique event and the associated impacts. For example - How sensitive is the climate to pCO2 change? How did Earth's biota respond to shifts in climate? These questions can be addressed by measuring the geochemical composition of microfossils that are found in marine sediments. In this study, novel geochemical analyses of two different types of microfossil: foraminifera (single-celled organisms that build their shell from calcium carbonate) and fossil fish teeth, will be used to reconstruct past environmental variables. Chemical analysis of planktonic foraminiferal shells will be used to reconstruct changes in sea surface temperature and acidity during the MECO event. The response of planktonic foraminifera, e.g., number of species, amount of each species and shell size, will also be recorded to assess any links between surface water changes and the response of the biota. Contemporaneous changes in bottom water conditions e.g., temperature and oxygen concentration, will also be assessed by analysing the geochemical composition of benthic foraminiferal shells and fossil fish teeth. Ultimately, study of past global warming events, such as the MECO, will provide a greater understanding of the links between pCO2 and global climate, which is essential to understanding Earth system behaviour. This work will provide new insights into the operation of the carbon cycle in a high pCO2 world and produce key data for the configuration and testing of numerical palaeoclimate and carbon cycle models. The research will be based within the School of Earth and Ocean Sciences at the University of Cardiff, which is actively investigating critical intervals of climate change in the geological past. I will also collaborate with scientists from other institutes notably, the National Oceanography Centre, Southampton and the University of South Carolina (see partnership details).