Isotopic composition of atmospheric CO2 inferred from carbon in C4 plant cellulose

The isotopic composition of atmospheric carbon dioxide provides an important constraint for models of the global carbon cycle. It is shown that carbon in C4 plants preserves an isotopic record of the CO2 used in photosynthesis. Data for the maize plant Zea mays yield results for the isotopic composition of atmospheric CO2 consistent with measurements of modern air and air trapped in polar ice. Data from C4 plants may thus be used to extend the isotopic record of atmospheric CO2 into the past, complementing data from other sources. (author)