Spatial Variation in the Marine Radiocarbon Reservoir Effect Throughout the Scottish Post-Roman to Late Medieval Period: North Sea Values (500–1350 BP)

N Russell,A J Dugmore,G T Cook,P L Ascough

doi:10.1017/s0033822200046245

N Russell, A J Dugmore + Show 2 more

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https://doi.org/10.1017/s0033822200046245

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Abstract

The marine radiocarbon reservoir effect (MRE) occurs as a spatially and temporally dependent variable owing to localized changes in oceanic water composition. This study investigates ΔR values (deviations from the global average MRE whose ΔR = 0) during the period 500–1350 BP for the east coast of Scotland, where a complex estuarine system exists that drains into the semi-enclosed North Sea basin. Due to the availability of suitable archaeological samples, the data set has a distinct Medieval focus that spans the area from Aberdeen in the north to East Lothian in the south. Many of the ΔR values are not significantly different from 0 (the global average), but there are occasional excursions to negative values (max –172 ± 20) indicating the presence of younger water. These values show greater variability compared to other published data for this general region, suggesting that considerable care must be taken when dating marine derived samples from archaeological sites on the east coast of Scotland.

Highlights

The marine reservoir effect (MRE) is a 14C age offset between contemporaneous terrestrial and marine samples that arises because of the extended residence time of carbon in the global marine reservoir
This study investigates R values during the period 500–1350 BP for the east coast of Scotland, where a complex estuarine system exists that drains into the semi-enclosed North Sea basin
Significant re-evaluation and re-interpretation of Scottish archaeological sites followed, where conclusions had previously been drawn that were based on dates from marine-derived carbon (Barber 2003). This allowed crucial re-interpretation of the relationships between Iron Age brochs and wheelhouses in Scotland (Ascough et al 2004). This current study extends the investigation of marine radiocarbon reservoir effect (MRE) to the east coast of Scotland, where a more complex topographical estuarine system exists, draining into the semi-enclosed North Sea basin

Summary

Introduction

The marine reservoir effect (MRE) is a 14C age offset between contemporaneous terrestrial and marine samples that arises because of the extended residence time of carbon in the global marine reservoir. In the absence of suitable terrestrial material, accurate and precise quantification of R is imperative for accurate calculation of calendar age ranges based on samples containing marinederived carbon. This is a critical factor in Scottish archaeology where, owing to our island location, prehistoric communities typically exploited a large coastal resource base. To demonstrate the effect of changing R values on radiocarbon calibrations, a hypothetical 14C date of 900 ± 35 BP was calibrated using OxCal 3.10 (Bronk Ramsey 1995, 2001) with a R of 100, a R of 100 and a R of 0, using the Marine curve (Hughen et al 2004) It is evident that R has a pronounced effect on the accurate calibration of marine-derived age measurements and any archaeological interpretation that may be based on that dating framework

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