Atmospheric carbon partitioning using 13C18O16O composition of CO2

Understanding the atmospheric CO2 budget is challenging and is critical for robust assessment of the importance of anthropogenic emissions in future projections of radiative warming of the Earth. Using an in-house purpose-built mass spectrometer, we propose to make the first ever measurements of the mass 47 (13C18O16O) anomaly in CO2 emitted by (a) fossil fuel burning power plants and (b) vegetation and soil, representing terrestrial biomass. In addition, we shall measure CO2 samples collected over the open ocean, far from these end-member sources. This parameter (mass 47 anomaly) describes the amount of 13C-18O bonds present within a population of carbon dioxide molecules, and is strongly temperature dependent. Because of this, processes taking place at different temperatures can be distinguished, and this is particularly valuable where the bulk isotopic signatures of the inputs to the atmosphere overlap. Previously, whilst it has been possible to distinguish between marine and terrestrial fluxes it has not been possible to characterise accurately the terrestrial flux because the carbon isotope signature of its two principal components, fossil fuel combustion, and photosynthesis and respiration of the terrestrial biomass, are almost identical. However, it should be possible to discriminate between them using this new approach since they originate through processes occurring at different temperatures. The proposed work will involve installing sampling tubing into a tall power station chimney, a forest canopy and a soil profile, and also on the deck of a research vessel. Sample ultra-purification will be done on a purpose built glass preparation line containing a cascade of cold traps, precisely calibrated volumes and very accurate pressure gauges, and a gas-chromatographic preparation column. Both this and subsequent sample measurement on the mass spectrometer are very time consuming and require great attention to detail in order to attain the necessary high precision. By identifying the mass 47 anomaly associated with different CO2 sources of atmospheric inputs, we hope to demonstrate that a further constraint can be introduced into calculations of the global CO2 budget and to build on this in future studies to refine understanding of the carbon cycle.