Cordilleran Section - 108th Annual Meeting (29–31 March 2012)

Paper No. 12
Presentation Time: 12:30


BERAMENDI-OROSCO, Laura E., Instituto de Geologia, UNAM, Ciudad Universitaria, Mexico DF, 04510, Mexico and GONZALEZ-HERNANDEZ, Galia, Instituto de Geofisica, UNAM, Ciudad Universitaria, Mexico DF, 04510, Mexico,

Atmospheric radiocarbon (14C) levels have been used to elucidate CO2 sources and its exchange with other carbon reservoirs. Specifically, given that fossil fuels are 14C-free due to their age, radiocarbon observations in CO2 from urban atmospheres can be used as direct tracer for fossil fuel-derived CO2 to estimate anthropogenic emissions. This approach has been mainly applied by 14CO2 analysis on instantaneous flask-collected air samples or by integrated samples obtained trapping CO2 in alkaline solution during longer time periods (weeks or months). However, both sampling approaches have limitations; the first yields samples representative of only a moment in time; and the second involves pumping large amounts of air through a concentrated alkaline solution limiting the spatial distribution of sampling sites.

Plant biomass incorporates 14C from the atmospheric CO2 so can potentially be used as indicators of the carbon isotopic composition of the local atmosphere at either high temporal resolution using short-lived plants, or at annual resolution using annual plants and tree-rings.

The aim of this study is to evaluate widely distributed short-lived plants as cheap and easy to sample bioindicators of atmospheric 14C variations related to fossil CO2 emissions with a high temporal resolution. We present a comparison between 14C data from integrated CO2 samples with two species of grass (Stenotaphrum secundatum and Lolium perenne) growing at the same sampling site inside Mexico City for the period 2008 – 2011. The main results suggest that both plant species do record variations in 14C atmospheric concentrations, showing similar trends to those found for integrated CO2 samples. This indicates that the carbon contained in leafs of both studied plant species has been recently assimilated. It can be concluded that it is possible to estimate fossil CO2 emissions with high temporal resolution from 14C concentrations in grasses growing in urban areas.