Climate change, seawater chemistry and planktic foraminiferal calcification in the Middle Eocene

The geological archive recovered from seafloor sediments documents in detail how the Earth has responded to millions of years of climate change and can be an invaluable means to investigate how the Earth system will react to our projected greenhouse future. Before 50 million years ago the Earth's climate was several degrees hotter than present, there was very little ice at the poles, and global sea levels were much higher. Between 50 and 34 Ma, the climate began to cool dramatically and extensive ice-sheets began to grow on Antarctica, taking the first steps towards the modern bipolar 'icehouse' world. However, this was not a unidirectional climatic cooling, but rather at this time Earth's climate fluctuated rapidly between short-lived warm intervals and times of possible icesheet cover on both hemispheres, in particular between 38 and 42 Ma (middle Eocene). These rapid fluctuations were likely driven by changes in the greenhouse gas CO2. The problem that we will address is that we lack a detailed record providing an accurate timing and reconstruction of these rapid climatic events which are necessary to understand the global and local climate conditions during this key transitional time interval. Here, we will look at the fossil remains of foraminifera: microscopic zooplankton that secrete intricate calcite (calcium carbonate) shells surrounding their cells which are preserved as minute fossils in huge numbers in seafloor mud. These microorganisms either live in the upper part of the ocean or on the seafloor and by looking at the chemical composition of their shells we can determine how warm, how acidic and how salty the ocean was when they were alive. To investigate Middle Eocene climate we will, firstly, determine exactly how old the sediments are that record climate change. We will do this by looking at the magnetic properties of the sediments which, combined with the chemical character of the foraminifera and the species present, act like a fingerprint indicating a specific age. Secondly, we want to document the detailed changes in environmental conditions recorded in the foraminiferal calcite geochemistry to produce a picture of the global climate through time. Third, we want to use this information to understand the effect rapid changes in atmospheric CO2, like that occurring today, have on ocean acidity and in turn on carbonate-producing plankton. Calcium carbonate dissolves in acid and given the importance of calcifying plankton as the base of the global marine foodchain, we need to know how they will respond. The research will be based at the National Oceanography Centre, Southampton, as part of the Palaeoceanography and Palaeoclimate research group, which is actively investigating critical intervals of climate change. We will collaborate with Scripps Institution of Oceanography, University of California at San Diego, where colleagues have specific expertise in the biology and calcification of foraminifera from the Eocene.