Investigating Marine Food Consumption in Prehistoric Humans via the δ13C values of Collagen Amino Acids

Philip Dunn1, Richard P. Evershed1 & C. Joshua Pollard2
1 School of Chemistry, University of Bristol, Organic Geochemistry Unit, School of Chemistry, Cantock's Close, Bristol, BS8 1TS, UK

2 Department of Archaeology and Anthropology, 43 Woodland Road, Clifton, Bristol BS8 1UU, UK

The current debate concerning the importance of marine foods in the diets of prehistoric peoples has stimulated interest in refining analytical approaches based on stable isotopes. An alternative to the widely bulk collagen approach is to investigate the stable carbon isotope composition of human bone collagen at the amino acid level. Our investigations of prehistoric humans from the Western Cape, South Africa, have shown that the Δ13CGlycine-Phenylalanine values for bone collagen amino acids correlate strongly with bulk δ15N values and provide a new proxy for marine food consumption. We are currently applying this new approach to human skeletal remains from northern Europe.
The tomb at Isbister lies on the south west coast of South Ronaldsay and is one of a number of Neolithic cairns found in the Orkney Islands.  During excavation in 1976, the stalled main chamber and three side chambers were found to contain some 16,000 human bones and bone fragments deriving from a minimum of 341 individuals along with a wide range of faunal remains.   Previous analyses of bone collagen from the human remains have shown that the tomb was in use from 4,500 to 3,800 BP and bulk collagen stable isotope values for 5 individuals lay in the range -19.9 to -21.2 ‰ indicating a predominantly terrestrial diet, which is surprising for people that lived so close to the coast. 
We have now employed the recently introduced LC-IRMS technique to determine the δ13C values of bone collagen amino acids from 22 individuals from Isbister. The results will be compared to those obtained by GC/C/IRMS. The derived Δ13CGlycine-Phenylalanine values give enhanced insights into the dietary habits of the people of Isbister.