I am currently working on using the carbon isotopic composition of paleosol carbonate to reconstruct spatial and temporal patterns of primary productivity in mid-latitude regions. The ratio of 13C to 12C in soil carbonate reflects the mixing of isotopically-distinct CO2 from two sources: atmospheric CO2 (~-7‰) and CO2 respired by plants and microbes in the soil (~-26‰). Previously, scientists used this ratio to track past changes in atmospheric CO2 levels. While this is one of the few methods that can reconstruct past atmospheric CO2 levels, for the Cenozoic, there are now a multitude of methods that can be used to estimate CO2. Thus, I am hoping to use these ratios to reconstruct the flux of soil-respired CO2, which is intricately linked with gross primary productivity on a landscape. Initial attempts at this method have been used to track changes in primary productivity in both Mongolia (Caves et al., 2014) and in northeast China (Gao et al., 2015).
Currently, a Stanford undergraduate–Samuel Kramer–is working to improve this method and recently presented his work at the Stanford Undergraduate Research Symposium (and won 1st place!). I am also presenting this work at the American Geophysical Union Fall Meeting 2015 in San Francisco.