G01_P10

Atmospheric radiocarbon analysis of grass samples; weekly resolution comparison and fossil fuel reconstruction of high traffic and background sites.

Usher E¹, Wood R², Esmay R¹, Fallon S¹

¹ANU Radiocarbon Dating Laboratory, Canberra, Australia, ²Oxford Radiocarbon Dating Laboratory , Oxford, UK

The atmosphere’s composition and dynamics, and particularly the role which carbon dioxide has within these, have become topics of increasing scientific importance in a world of anthropogenic climate change. The radioisotope composition of atmospheric CO₂ is an integral component for these topics as it can allow for anthropogenic influence to be identified and even quantified due to the Suess effect. Biotic assimilation proxies present an avenue to investigate atmospheric ¹⁴C at varying temporal and spatial scales. Grass as a biotic proxy has successfully been used to reconstruct fossil fuel contribution to atmospheric CO₂ in a point source analysis by Turnbull et al. (2016). In this work grass samples from three locations, two background and one sample site, will be analysed for F¹⁴C values in order to reconstruct the fossil fuel contribution (CO₂ff) from traffic next to one of Canberra’s busiest roads, Parkes Way Road. Grass is sampled weekly from these sites and cryogenically frozen until pre-treatment, then measured with an AMS. This work uses a relatively novel biotic proxy to identify emissions contributions from motor vehicles in Canberra. The early results from this study show that there is a measurable difference in F¹⁴C values between the background sites and the road site consistent with an average of ~4ppm contribution from CO₂ff. 

Turnbull, J, Keller, E, Norris, M, Wiltshire, R. (2016). Independent evaluation of point source fossil fuel CO₂ emissions to better than 10%. Proceedings of the National Academy of Sciences. 113. 201602824. 10.1073/pnas.1602824113.