Late pleistocene-recent atmospheric δ13C record in C4 grasses

Samples of Setaria species from packrat middens, herbarium specimens and modern plants preserve a record of δ13C of atmospheric CO2 from 12,600 Bp to the present. No secular trend is detected between 12,600 and 1,800 Bp, when the mean value of δ13C during that period was -6.5 ± 0.1 per-thousand (the error is the standard deviation of the mean). The value agrees with δ13C averages of pre-industrial CO2 from polar ice cores, and differs significantly from modern regional (-8.2 ± 0.1 per-thousand) and global (-7.7 per-thousand) values, which are higher because of fossil fuel burning