Influence of marine sources on 14C ages:: isotopic data from Watom Island, Papua New Guinea inhumations and pig teeth in light of new dietary standards

Gauging the effect of C-14-depleted marine foods on radiocarbon ages requires an accurate assessment of the likely proportion of marine foods in the diet. Several factors must be considered, including region-specific delta C-13, delta N-15 and delta S-34 data values (regional stable isotope values can differ from global averages), temporal variations in delta C-13 which offset values in modern dietary standards by up to 1.5 parts per thousand, and that modelling which considers only delta C-13 may overestimate the contribution of various dietary sources. Here, we compare previous calculations by linear interpolation of delta C-13 and a complex computer simulation of marine contribution to the diet of inhumations from the SAC archaeological site Watom Island, Papua New Guinea, with the ISOSOURCE mixing model and a revised database of regional dietary sources and their isotopic values, to estimate marine diet contributions and radiocarbon offsets for burials from the SAC site. Though different estimates of marine contribution to diet do not significantly alter previous calibrations of radiocarbon ages for the inhumations, the new ISOSOURCE calculations challenge the idea of excessive exploitation of marine resources and support evidence for arboriculture and horticulture being a major component in Lapita diet.