Stable carbon isotope ratios of soil organic matter and their potential use as indicators of palaeoclimate

The δ¹³C values of soil organic matter record information regarding the relative importance of C₃ versus C₄ plants in past plant communities. Because the geographical distribution of C₄ plants is correlated strongly with temperature, δ¹³C of soil organic matter has the potential to enhance understanding of climate history. The purpose of the paper was to: (1) demonstrate that δ¹³C of soil organic matter responds to and records changes in the relative abundances of C₃ and C₄ plants in situations where plant community histories are well known; then (2) apply this technique to soil organic matter in palaeosols representing the past 15 000 years in order to reconstruct vegetation and climate change during that period. The δ¹³C values of soil organic matter accurately documented vegetation dynamics at two sites where land use and vegetation history had been quantified previously: a tallgrass prairie and a subtropical woodland. Changes in δ¹³C values of organic matter in palaeosols from central Texas indicated shifts in the relative abundance of C₃ and C₄ plants which tracked changes in climate indicated from accounts published previously and based on other climate reconstruction techniques. Results indicate that δ¹³C of soil organic matter, by reflecting the relative contribution of C₃ and C₄ species to plant community productivity, can be used to reconstruct vegetation history and can therefore serve as a proxy indicator of past climate.