Isotopic δ13C and δ15N values in archaeological human and animal collagen in relation to average annual precipitation: A case study of Northern Mesopotamia

Isotopic analysis of bone and dentine collagen has become a standard tool for reconstructing archaeological human and faunal diet. There is a known correlation between carbon and nitrogen isotope values and precipitation but typically this is left unquantified. When accounted for in archaeological studies, this relationship has been presented as a linear regression model. To better understand the impact of precipitation to carbon and nitrogen stable isotopic values in Northern Mesopotamia where precipitation is variable, we pooled data from 12 archaeological sites to test δ15N and δ13C in human and domesticated ruminant remains against local annual precipitation estimates. The results show that precipitation explains a higher amount of the variation in δ15N than δ13C. Animal data generally fit a linear model while humans are better represented by non-linear models.