Species-specific reservoir effect estimates: A case study of archaeological marine samples from the Bering Strait.

Alison Jt Harris,Maria Dobrovolskaya,Peter Jordan,Arkady Savinetsky,Kerstin Lidén,Gunilla Eriksson,Johannes Van Der Plicht,Jack Pr Dury,Kirill Dneprovsky

doi:10.1177/09596836211041728

Abstract

Due to the marine reservoir effect, radiocarbon dates of marine samples require a correction. Marine reservoir effects, however, may vary among different marine species within a given body of water. Factors such as diet, feeding depth and migratory behaviour all affect the 14C date of a marine organism. Moreover, there is often significant variation within single marine species. Whilst the careful consideration of the ΔR values of a single marine species in a given location is important, so too is the full range of ΔR values within an ecosystem. This paper illustrates this point, using a sample pairing method to estimate the reservoir effects in 17 marine samples, of eight different species, from the archaeological site of Ekven (Eastern Chukotka, Siberia). An OxCal model is used to assess the strength of these estimates. The marine reservoir effects of samples passing the model range from ΔR (Marine20) = 136 ± 41–ΔR = 460 ± 40. Marine reservoir effect estimates of these samples and other published samples are used to explore variability in the wider Bering Strait region. The archaeological implications of this variability are also discussed. The calibrating of 14C dates from human bone collagen, for example, could be improved by applying a dietary relevant marine reservoir effect correction. For humans from the site of Ekven, a ΔR (Marine20) correction of 289 ± 124 years or reservoir age correction of 842 ± 123 years is suggested.

Highlights

IntroductionMarine reservoir effectsTerrestrial organisms acquire carbon from the atmosphere (either directly or indirectly); there are other ‘reservoirs’ of radiocarbon, such as marine bodies of water
Marine reservoir effectsTerrestrial organisms acquire carbon from the atmosphere; there are other ‘reservoirs’ of radiocarbon, such as marine bodies of water
This model calibrated all terrestrial samples in a single phase with an outlier test; the goose sample (EKV35) was not identified as an outlier among the other terrestrial samples, demonstrating its fit within the terrestrial dataset. Whilst it is possible for a reservoir age of 235 ± 40 years (ΔR = −307 ± 39) to be measured in a marine sample, given the poor statistical fit of the 14C date of EKV01 among the other fauna, it is more likely the sample became incorporated into the grave context through bioturbation or animal action

Summary

Introduction

Marine reservoir effectsTerrestrial organisms acquire carbon from the atmosphere (either directly or indirectly); there are other ‘reservoirs’ of radiocarbon, such as marine bodies of water. Aquatic organisms generally have a lower 14C/12C ratio than atmospheric CO2, leading to samples yielding older ‘apparent ages’. For marine organisms, this ‘marine reservoir effect’ (MRE) can be many 100s of years (Heaton et al, 2020). The reservoir age, R(t), of such a sample, is defined as the difference between the measured 14C age of an aquatic sample and that of a contemporaneous terrestrial (atmospheric) sample (Stuiver et al, 1986). MREs can vary geographically due to factors such as deepwater upwelling and sea ice cover (Heaton et al, 2020).

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