Non-linear relationship between bulk δ13C and percent maize in carbonized cooking residues and the potential of false-negatives in detecting maize

Bulk δ13C values on charred cooking residues adhering to pottery sherd interior surfaces have been used as a source of information on the histories of maize in various locations in the western hemisphere. This approach is based on an assumption of a linear relationship between the percent maize in the resource mix cooked in a pot and δ13C. Previous experiments suggest that this relationship is non-linear, and maize may not be identified from bulk δ13C values even when it contributed substantially to the resource mix. A second round of experiments, presented here, indicates that the mobilization of carbon from maize and C3 resources over time is the critical variable in residue formation and the resulting bulk δ13C value. This is influenced by the form of maize being cooked.