Carbon and nitrogen stable isotope analysis on the diet of Jomon populations from two coastal regions of Japan

We report on a stable isotope paleodietary reconstruction of Jomon populations in Japan during the Middle to Final Jomon period (ca. 5000-2300 years BP), focusing on dietary differences within and among populations and between regions. Carbon and nitrogen isotope analysis was performed on human and faunal bone collagen from six coastal sites along the Inland Sea in the Sanyo (Ota, Funamoto, and Tsukumo) region and along Mikawa Bay and the Pacific Ocean in the Tokai (Kawaji, Yoshigo, and Inariyama) region. We found that carbon and nitrogen isotope ratios were positively correlated, indicating that the Jomon people consumed a mixed diet of marine (shellfish and marine fish) and terrestrial (C₃ plants and terrestrial mammals) protein. In the Ota samples (n=25, during the Middle Jomon period, 5000-4000 years BP), sex was one of the main reasons for the intra-population dietary variation. Ota males consumed greater amounts of marine food, while Ota females consumed greater amounts of terrestrial food; these dissimilar diets may have been related to the sexual division of labor. Significant inter-population dietary differences were found, which may have been related to differences in age or site location. Notably, the two coastal regions showed clear isotopic differences. Nitrogen isotope ratios of individuals from the Sanyo region were significantly higher than ratios of individuals from the Tokai region. The individuals in the Sanyo region might have consumed a diet high in aquatic foods, particularly high trophic level marine fish, whereas the individuals in the Tokai region might have consumed a lot of marine shellfish. Another possible reason for the regional isotopic difference might have been different baseline of nitrogen isotope ratios of the marine ecosystems.