Journal of the Royal Society of New Zealand abstracts

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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

Nancy Beavan Athfield¹, Roger C. Green², Jacqueline Craig², Bruce McFadgen³, and Simon Bickler⁴

¹Rafter Radiocarbon, GNS Science, 30 Gracefield Road, Lower Hutt 5010, New Zealand.

²Anthropology Department, The University of Auckland, Private Bag 9 - , Auckland 1142, New Zealand.

³99 Sefton Street, Wadestown 6012, Wellington.

⁴Bickler Consultants Ltd, Auckland.

Abstract Gauging the effect of ¹⁴C-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 δ¹³C, δ¹⁵N and δ³⁴S data values (regional stable isotope values can differ from global averages), temporal variations in δ¹³C which offset values in modern dietary standards by up to 1.5‰, and that modelling which considers only δ¹³C may overestimate the contribution of various dietary sources. Here, we compare previous calculations by linear interpolation of δ¹³C 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.

Keywords    Watom Island; Lapita; marine offsets; calibration; mixing models; dietary standards

R07008; Received 18 June 2007; accepted 15 February 2008; Online publication date 11 March 2008

Journal of the Royal Society of New Zealand
Volume 38, Number 1, March, 2008, pp 1–23

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