02.11.2015: FB2-Seminar

13:00 Uhr, Hörsaal, Düsternbrooker Weg 20

Abstract:

Carbon dioxide is the greenhouse gas that to a large extent dictates the climatic state of the Earth on long timescales, and yet we know very little for certain about how its atmospheric abundance varied in the geological past. Prior to 800ka, which is the temporal extent of pCO2atm records from bubbles trapped in ice, proxies based on the isotopic composition of organic matter from phytoplankton have dominated Cenozoic pCO2atm reconstructions. The basis of these proxies is the well-documented effect of the variation in passive CO2 supply to the cell at different CO2 concentrations on the apparent magnitude of isotopic fractionation of carbon into organic matter. However, although a plethora of additional factors contribute to this apparent fractionation, these have until now been universally treated as a black box. Here I use a novel protocol for the extraction and isotopic analysis of a specific type of organic macromolecule, preserved within sedimentary coccolith calcite, to reconstruct, for the first time, organic and inorganic carbon isotopes from ancient cells of known size and taxonomic affiliation. I further interpret these data using a new model of carbon isotopes in coccolithophores, calibrated in vivo,  to extract a  [CO2] signal from isotopic compositions.  Through analysis of sediments spanning a glacial cycle, a real-world proof of concept of this novel approach reveals that the carbon isotopic composition of organic and inorganic matter is sensitive to changes in [CO2] even over the subtle range of [CO2] change that typifies a glacial cycle.