Chemical profiling of ancient hearths reveals recurrent salmon use in Ice Age Beringia

Abstract

Current approaches to reconstruct subsistence and dietary trends in ancient hunter-gatherer societies include stable isotope analyses, but these have focused on human remains, cooking pottery, and food residues, which are relatively rare in the archaeological record. In contrast, short-term hearths are more ubiquitous worldwide, and these features can provide valuable evidence for ancient subsistence practices, particularly when faunal remains are not preserved. To test the suitability of hearths for this purpose, we conducted multiple chemical analyses: stable carbon and nitrogen isotope analyses of total organic matter (expressed as δ13C and δ15N values) and compound-specific carbon isotope analyses of individual fatty acids (δ13C16:0 and δ13C18:0) from 17 well-preserved hearths present in three occupations dating between ∼13,200–11,500 calibrated years B.P. at the Upward Sun River (USR) site in central Alaska. We combined δ15N and δ13CFA data in a Bayesian mixing model (stable isotope analysis in R) with concentration dependency to each hearth. Our model values were tested against faunal indices, indicating a strong positive relationship between marine proportional contributions to each hearth and salmon abundance. Results of the models show substantial anadromous salmon use in multiple USR components, indicating recurrent use of the site for salmon processing during the terminal Pleistocene. Our results demonstrate that salmonid and freshwater resources were more important for late Pleistocene hunter-gatherers than previously thought and highlight the potential of chemical profiling of hearth organic residues for providing greater geographic and temporal insights into resource use by prepottery societies.